Management of the Difficult and Failed Airway, 2e

Chapter 5. Aspiration: Risks and Prevention

Saul Pytka; Edward Crosby; Idena Carroll

5.1 Introduction

Pulmonary aspiration, an uncommon occurrence in nonemergency airway management, may lead to a spectrum of sequelae, from no discernable effects to significant morbidity and mortality. In this chapter, we will outline the known factors that increase the risks of aspiration and how airway management may be optimized to reduce the risks to the patient.

Although reported in the literature as a relatively uncommon complication of nonemergency airway management, a majority of airway practitioners will acknowledge that the risk of aspiration is a major concern to them in daily practice. Most would acknowledge that if they have not had an episode of aspiration in one of their patients, they know a colleague who has had to deal with the complication. Kluger and Willemsen1 reported in 1998 that over 71% of all anesthesiologists responding to a national mail-in survey in New Zealand had had at least one case of aspiration in their careers.

5.2 Historical Perspective

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5.2.1 When Was Gastric Aspiration First Described?

Mendelson was the first to describe the occurrence of aspiration in conjunction with the delivery of obstetrical anesthesia.2 Since that time, a plethora of publications have followed, outlining the risks and ways of preventing the problem. Unfortunately, much of the information is conflicting, and conclusions have been derived from studies with surrogate endpoints that may have very little to do with actual clinical risks. For example, the often-quoted study by Roberts and Shirley3 suggested a gastric volume of greater than 25 mL and pH of less than 2.5, as a specific risk factor for aspiration. This postulation was accepted by subsequent investigators who directed their efforts for prevention of aspiration to the assumption that these specific values were critical factors in predicting the outcome of aspiration.

5.2.2 What Was Sellick's Approach to Minimize the Risk of Gastric Aspiration?

In the discussion section of his 1961 paper advocating the use of cricoid pressure during the induction of anesthesia to prevent the aspiration of gastric contents, Sellick examined alternatives available at the time.4 He identified inhalational induction in the supine or lateral position (with head-down tilt) and rapid IV induction of anesthesia in the sitting position. He commented that, with inhalational induction, vomiting usually occurred in lighter stages of anesthesia when protective reflexes were hopefully still present and noted that any difficulty during induction predisposed to regurgitation and anoxia. Rapid IV induction in the sitting position often led to cardiovascular collapse in critically ill patients, and pulmonary aspiration was made more likely by the sitting position, if gastric reflux occurred. Sellick advocated the use of cricoid pressure during induction of anesthesia as a third option.

Sellick suggested that the stomach should be emptied before induction and the nasogastric tube then be removed. He was of the opinion that the nasogastric tube would prevent esophageal occlusion with cricoid pressure. The patient was positioned with the head and neck fully extended and, following denitrogenation, induction ideally occurred with an IV barbiturate-muscle relaxant combination. Cricoid pressure was instituted before induction, moderate pressure was applied during induction, and this was increased to firm pressure once consciousness was lost. Sellick suggested that the lungs may be ventilated without risk of gastric regurgitation. Once intubation was completed and the cuff inflated, cricoid pressure could be safely released.

In his description of cricoid pressure, Sellick reported its application in 23 high-risk cases. He noted no instance of pulmonary aspiration in any patient but did report that, in three cases, release of cricoid pressure after intubation was followed immediately by reflux into the pharynx of gastric or esophageal contents, suggesting that cricoid pressure had indeed been effective.

5.3 Incidence and Risk

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5.3.1 What Is the Incidence of Aspiration in Anesthesia Practice?

The difficulty in determining the actual incidence of aspiration relates to a number of factors. Firstly, because it occurs rarely, studies addressing the topic need to be very large. Most, if not all, of the better studies to date have been derived from large computerized databases. Secondly, aspiration is not always easy to recognize and, as will be illustrated below, rarely leads to clinical findings, let alone serious sequelae. Hence, it is an event likely to be missed and therefore underreported.

The recognition of gastric material in the pharynx does not alone support a diagnosis of aspiration. Despite the evident regurgitation, pulmonary aspiration may not have occurred. Even if foreign material is seen below the level of the true vocal cords, there may be a wide spectrum of clinical consequences. Silent aspiration may occur, wherein the patient exhibits no signs or symptoms of aspiration and there are no disruptions of physiological parameters. Indeed, it has been reported that asymptomatic aspiration may occur in up to 45% of normal subjects during sleep, and as many as 70% of people who have a blunted level of consciousness and responsiveness.5

Aspiration may become symptomatic, with cough and audible wheeze. Acute lung injury may be associated with tachypnea, increase in alveolar-arterial (A-a) gradient, hypoxemia, and radiological evidence of lung injury—with infiltrates and/or atelectasis. Frank respiratory failure may ensue, with the development of acute respiratory distress syndrome (ARDS), the need for ventilatory support, and (rarely) death.

Although many papers have reviewed the topic of aspiration, there has been a notable absence of consistent end points. In 1993, Warner6 published a retrospective review of 215,488 general anesthetics over a period of 6 years. Aspiration was defined as:

…either the presence of bilious secretions, or particulate matter, in the tracheobronchial tree; or, in patients who did not have their tracheobronchial airways directly examined after regurgitation, the presence of an infiltrate on postoperative chest roentgenogram that was not identified by preoperative roentgenogram, or physical examination.

Of the anesthetics included, 202,061 were elective and the remaining 13,427 were emergency cases. There were 52 and 15 aspirations in these two groups, respectively. The overall incidence of aspiration was 1:3216. Aspiration occurred in 1:3886 of elective surgeries and 1:895 of emergency procedures. Sixty-seven cases of significant aspiration were recognized; one patient died from surgical causes intraoperatively. Of the remaining 66 patients, 42 (64%) experienced no obvious sequelae from the aspiration. Of the remaining 24 patients, 13 required mechanical ventilation with 6 needing prolonged (>24 hours) mechanical support. Half of these (three) died of complications from their aspiration, giving a death rate of 1:71,829.

Mellin-Olsen,7 in 1996, reported a prospective review of 85,594 cases over a 5-year period. They defined aspiration as "what the anesthetist has interpreted as such during, or immediately after the anesthetic procedures, based on clinical signs like gastric content, in the pharynx/larynx/trachea and a drop in O2 saturation." In their study, a total 25 cases of aspiration were recorded; 52,650 patients had received a general anesthetic, with the remainder undergoing either regional or IV sedation. All cases of aspiration occurred in the general anesthetic population, giving an incidence of 1:2106. The incidence of aspiration was 1:3303 in elective procedures under general anesthetic and 1:809 for emergency procedures, both rates similar in magnitude to those reported by Warner. In the patients who had aspirated, there were similar complications to those described by Warner.6 No deaths occurred and 22/25 patients had either no or minimal sequelae; three experienced more serious consequences. One patient required ventilation for 7 days, but made a complete recovery from his lung injury.

Olsson et al8 reported a similar retrospective review, with an incidence of aspiration of 1:2131 and a mortality rate of 1:46,000. Finally, Sakai et al9 conducted a 4-year retrospective review of 99,441 anesthetics at a single American university hospital. There were 14 cases of confirmed pulmonary aspiration for an incidence of 0.014% or 1:7103 overall. Seven cases of aspiration occurred in gastroesophageal procedures and patients in whom aspiration occurred had one or more identifiable risk factors. Six patients developed pulmonary complications related to the aspiration and one died. All these studies reaffirm that aspiration is a relatively uncommon occurrence and the mortality due to aspiration in the perioperative period is rare.

Kluger and Short10 reported, in 1999, the analysis of data from the Australian Anaesthetic Incident Monitoring Study (AIMS). AIMS is a voluntary, anonymous reporting system of anesthesia-related incidents, collected in a central database. Unfortunately, the nature of this type of study does not allow for a denominator (ie, the total number of anesthetics performed by all reporting clinicians) and the incidence is unavailable. Of the 5000 reported events, 133 dealt with aspiration. Aspiration was deemed to have occurred if "any obvious nonrespiratory secretions were suctioned via a tracheal tube, there was chest X-ray evidence of new pathology after an incident, and/or there were signs of new wheeze or crackles after an episode of regurgitation or vomiting." In this group of 133 aspirations, 5 deaths were recorded. Of interest, aspiration did occur in a number of patients undergoing regional anesthesia in the AIMS study (7 out of the 133), whereas none were reported to have occurred in almost 31,000 regional and sedation cases in the paper by Mellin-Olsen et al.7

The American Society of Anesthesiologists (ASA) Closed Claims Database reviewed the incidence of aspiration as a cause of liability to anesthesiologists. In 2000, Cheney11 reported that aspiration represented 3.5% of all claims as a primary or secondary event, and in half of those it was the offending event leading to a claim. Seven percent of the aspiration claims were during regional anesthesia.

In conclusion, the incidence of aspiration in a population is consistently estimated at between 1:2000 and 1:4000, depending on the population studied, and when the data had been reported. Emergency surgery increases the risk of aspiration fourfold, or more, yet overall mortality remains low.

5.3.2 What Are the Risk Factors that Contribute to Aspiration? What About Nonanesthesia Settings?

In published studies measuring the incidence of aspiration, the most common association was with emergency surgery.6-8,10,11 Olsson8 reported that the timing of surgery also correlated with an increased incidence of aspiration, with a sixfold increase in the rate of aspiration between 18:00 and 06:00 hours. The causative factors that relate to the increased risk of aspiration with emergency surgery are not outlined in the studies, but numerous issues such as lack of fasting, stress, depression of GI motility, less staff availability, higher dependence upon less-experienced anesthesia staff, and fatigue may all play contributing roles. A preponderance of the cases of aspiration reported by Olsson8 occurred in patients who had abdominal surgery performed, with esophageal and upper abdominal procedures predominating. The incidence of aspiration in cesarean section was 1:661. Interestingly, Warner,6 roughly 10 years later, had no cases of aspiration during cesarean section. In another paper reviewing the incidence of aspiration in children, Warner12 reviewed 63,180 anesthetics in children under the age of 18 and also found the incidence of aspiration in the emergency patient (1:373) to be significantly higher than that in the elective situation (1:4544).

There is a paucity of well-controlled, clinical trials that examine the incidence of aspiration in the prehospital and emergency department (ED) settings. In the prehospital setting, the rates of occurrence of aspiration vary from 6% to 90%, depending on the study populations and facilities, and whether the study considered survivors, nonsurvivors, or postmortem examinations.13,14 Often, aspiration had already occurred prior to attempted intervention and provision of care. In some papers, the incidence of failure to intubate the trachea is as high as 47%.14,15,16 In the study by Gausche,15 patients were randomized into intubation group versus transport by bag-mask. There was an intubation success rate by the paramedics of only 57% and the only aspirations occurred in the intubation group. The outcomes between the two groups, in terms of survival, were similar. In the prehospital literature, the source of aspirate in trauma patients differs from that of the emergency surgical population. In the study by Lockey,13 34%, or a total of 18 of the trauma patients, had evidence suggestive of aspiration. Of these, 15 had blood contaminating their airway, while only 3 had evidence of gastric contents. All had significant head injuries, with a Glasgow Coma Scale of 8 or less.13

Taryle reviewed 43 consecutive intubations in the ED in a major teaching institution and reported a total of 38 complications in half of the patients (22/43). Aspiration occurring prior to airway manipulation was not included as an aspiration within their data. There were eight aspirations; the second most common complication after prolonged intubating time.17 Sakles18 reported a 1-year review of all intubations in an ED that had a census of 60,000 patients per year. In 610 consecutive intubations, 49 patients had a total of 57 immediate complications. Although there were 10 cases of vomiting, they did not report any occurrences of aspiration. Mort,19 while reporting on airway complications during emergency intubation occurring outside of the operating room, noted that fewer aspirations occurred in the ED than on the wards or the medical ICU. The obstetrical population will be discussed later in this chapter.

5.3.3 What Happens during an Aspiration that Determines Its Severity?

The consequences of aspiration can occur as a result of a chemical injury to the airway mucosa from either acid or bile. Injury may occur from particulate material in the aspirate causing either airway obstruction, or an inflammatory response. Finally, there may be pneumonia secondary to contamination from bacteria in the stomach or upper airway.

Injury resulting from aspiration is often that of an acute chemical burn and is a function of both volume and pH of the aspirate. Subsequent release of inflammatory substances, such as cytokines and interleukins from injured tissue, provokes neutrophil migration to the affected areas and further airway reaction. Airway edema, as well as capillary leak in the alveoli, can increase airway resistance and worsen lung compliance. The end result is ventilation–perfusion mismatching and hypoxemia, as well as inflammatory infiltration and/or atelectasis.

The initial chemical burn effect occurs within seconds, followed by neutralization of the acid within 15 seconds. The sudden onset of bronchospasm and laryngospasm may occur. Full evolution of injury can take several days. Repair of the injury is of the order of 3 to 7 days. Particulate materials can induce a local reaction themselves and lead to a pneumonia. Indeed, attempts to neutralize the gastric pH with particulate antacids may aggravate reaction in the lung due to the particles rather than from the acid itself. Particulate materials of sufficient size or number can produce substantive airway obstruction in their own right.

Pneumonia may follow, related to organisms from the upper airway, esophagus, and stomach. This is usually of a mixed flora, with anaerobes and aerobes present. Depending on the organism and the premorbid condition of the patient, this may progress to lung abscess. This is unlikely in the healthy patient. Differentiating between inflammatory pneumonitis and pneumonia may be difficult. The clinical and radiological picture may be similar. Pneumonitis is usually acute, resolving in hours to a day. If the presentation is one of progression without resolution, lasting days, with fever and purulent sputum, a diagnosis of pneumonia is more likely.20-24

5.4 Patient Populations at Risk

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5.4.1 What Is the Relevance of the Issues of Gastric Volume, pH, and Constituency of the Gastric Contents?

Roberts and Shirley3 concluded that a pH of less than 2.5 and a gastric volume of 25 mL (or 0.4 mL·kg−1) correlated with aspiration and resultant pneumonitis. In their study, an acid solution was injected directly into the bronchus of a monkey and extrapolations were made in regard to the volume and pH that would place humans at risk. These conclusions have been challenged by numerous investigators.25,26 Schreiner26 in 1998 pointed out that over 30% to 60% of patients have a gastric fluid volume of greater than 0.4 mL·kg−1 (median 0.3, but as high as 4.5 mL·kg−1), yet the incidence of aspiration is quite rare. Indeed, it has been demonstrated that the incidence of gastroesophageal reflux (GER) is not associated with residual gastric volume (RGV).27 Rather, it has been shown that GER during anesthesia is related to episodes of straining on an endotracheal tube when inadequate anesthesia has been provided.28

Maltby25 argues that the risk of aspiration is due to loss of the barrier pressure at the gastroesophageal sphincter (GES), also referred to as the lower esophageal sphincter (LES). Normally, stomach contents are prevented from refluxing into the esophagus by the pressure exerted by the LES. The difference between LES pressure and intragastric pressure is the barrier pressure. The stomach is a very compliant structure and intragastric pressure can remain stable until volumes greater than 1000 mL are present.29 Indeed, as intragastric pressure rises, because of its anatomical design, so does LES pressure, maintaining the barrier pressure. In one study, measurements of the intragastric pressure and LES pressure during laparoscopy demonstrated that a rise in mean gastric pressure from 5.2 to 15.7 was matched by a rise in LES tone from 31.2 to 47.0 cm H2O.30

There is a clear association between aspiration and vomiting or gagging.1,6-8,10 With active vomiting, or gagging, the sudden onset of high intragastric pressure is associated with relaxation of both the lower and upper esophageal sphincter mechanisms. This combination enhances the risk of pulmonary aspiration.

The higher the baseline intragastric pressure, the greater the tendency for GER and pulmonary aspiration. With an intestinal obstruction, for example, the intragastric pressure is high in association with the large RGV. This accounts for the high incidence of aspiration in this patient population and the finding that it is one of the most common factors associated with aspiration in most publications. By the same reasoning, patients with a documented hiatal hernia, or a history of GER disease (GERD), are also exposed to a higher risk of regurgitation and aspiration.

Active vomiting, in association with an unprotected airway, is most likely to occur during induction of anesthesia, with airway manipulation prior to placement of the endotracheal tube, and at the end of a procedure as the patient is awakening and the airway is no longer protected. Inadequate levels of anesthesia at these times, as well as difficulty securing an airway, are the essential elements favoring the occurrence of aspiration. Two-thirds of aspiration events are reported during induction and extubation, equally divided between the two periods.6

5.4.2 How Important Is a History of Heartburn? Acid Taste or Burping? a History of GERD? How Much Reflux Is Significant?

Reflux occurs when the barrier pressure fails to prevent gastric contents moving from the stomach into the esophagus. Intuitively, those with a clear history of reflux should be at greater risk of aspiration. Kluger10 found that a history of reflux and hiatal hernia were the ninth and tenth most common predisposing factors for aspiration, representing 7 and 6 cases, respectively, in the database of 133 total cases of aspiration. The patient with a history of acid reflux, with complaints of acid taste or choking at night, represents a more significant risk than one with only complaints of heartburn. The latter may simply suggest gastric mucosal pathology. However, no specific data are available to indicate that one symptom is more helpful than another in identifying who is at greater risk. Again the larger the volume of reflux, the more significant is likely to be the risk of aspiration.

5.4.3 What Clinical Situations and Characteristics Predispose to Aspiration?

5.4.3.1 Emergency Surgery

Emergency surgery is the most significant risk factor associated with aspiration in the studies outlined earlier, increasing the incidence of aspiration by four- to sixfold.6

5.4.3.2 ASA Physical Status

When Warner6 compared the ASA status to the risk of aspiration in elective situations, the risk or aspiration increased by almost sevenfold as ASA status rose from I to IV or V. In emergency situations, the occurrence of aspiration increased from 1:2949 for ASA I patients to 1:343 for ASA IV and V patients, or almost a ninefold increment (Table 5-1). Olsson8 also reported an increased risk of aspiration and increased morbidity with increasing ASA status. Most, if not all, of the reported aspiration-associated deaths occur in ASA IV and V patients.

Table 5-1 Risk of Pulmonary Aspiration in Elective and Emergency General Anesthetics by ASA Physical Status Classification

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Table 5-1 Risk of Pulmonary Aspiration in Elective and Emergency General Anesthetics by ASA Physical Status Classification

ASA PHYSICAL STATUS

ELECTIVE

EMERGENCY

4/36,916 (1:9,229)

1/2,949 (1:2,949)

.319

11/82,436 (1:7,494)

3/5,036 (1:1,679)

.043

III

31/74,301 (1:2,397)

8/4,413 (1:552)

Less than .001

IV and V

6/8,409 (1:1,401)

3/1,029 (1:343)

.066

Total

52/202,061 (1:3,886)

15/13,427 (1:895)

Less than .001

See reference 6.

5.4.3.3 Airway and Intubation Difficulties

Difficult intubation is associated with an increased risk of aspiration. Vomiting during airway interventions is frequently associated with aspiration, far more so than passive regurgitation. In Olsson's paper,8 out of 15 cases of aspiration in elective patients in which no risk factors predisposing to aspiration could be identified from the chart review, 10 (67%) had difficulty with intubation preceding the vomiting and aspiration. In total, 58 out of the 87 patients who aspirated did so due to difficulty with intubation or, with airway manipulation. Warner6 described aspiration in 69% of his patients in whom active vomiting or gagging occurred during intubation or extubation. Mort demonstrated that when the number of intubation attempts went from ≤2 to greater than 2, a significant increase in complications occurred. The incidence of regurgitation rose from 1.9% to 22% and aspiration from 0.8% to 13%, directly correlated with an increase in the number of intubation attempts.19 Sakai et al9 reported that 5 of 16 reported aspirations occurred during laryngoscopy or airway interventions including the exchange of airway devices in at-risk patients.

In summary, there are multiple studies describing morbidity and mortality associated with airway interventions and difficulties.19,31-33

5.4.3.4 Obesity

There was no correlation between obesity and aspiration in the studies by Warner et al6 or Mellin-Olson et al.7 Olsson,8 however, did find obesity to be a contributing factor for aspiration risk. Obesity is frequently listed as an aspiration-associated factor in many other references. The association of obesity with an elevated risk of aspiration may relate to a high incidence of pertinent comorbidities. For example, delayed gastric emptying is known to be associated with diabetes, which is a more frequent finding in the obese. Other factors related to the obese include GER, difficult intubation, and inadequate anesthesia at the time of induction. This may account for the larger number of obese patients reported in aspiration populations.10

Obese patients have the same gastric emptying rate for liquids as nonobese patients. Depending on the meal content, the gastric emptying in obese patients for solids may be faster, slower, or the same as in the nonobese patients.25,34-37 Maltby25 reported that obesity did not slow gastric emptying in the absence of other predisposing comorbid conditions and suggested that fasting guidelines should be applied to obese patients using the same criterion as for the nonobese. In their paper, obese patients, with no comorbid conditions, were randomized into fasting and nonfasting groups. The later received a 300-mL clear-fluid challenge preoperatively, with no difference in RGV demonstrated postintubation between the two groups. A study reviewing anesthesia for electroconvulsive therapy in 50 obese patients reported no cases of aspiration in 660 procedures.38

5.4.3.5 Pregnancy

It has been well accepted that the obstetrical population is at increased risk of aspiration. This has been felt to be secondary to a number of factors. Hormones, particularly progesterone, cause relaxation of the LES and impair gastric emptying. Mechanical effects of the gravid uterus alter the position of the stomach and, as term approaches, create a gastric pinchcock partially obstructing the gastroduodenal junction. The gravid uterus also increases intra-abdominal pressure, which then increases intragastric pressure. It has been demonstrated that the intragastric pressure in pregnancy is increased to 17.2 cm H2O from the nonpregnant level of 7.3 cm H2O. Women experiencing heartburn in pregnancy have a drop in the LES tone from the normal in pregnancy of 44 cm H2O to 24 cm H2O. Heartburn in pregnancy is reported in some series to be between 45% and 70%, with 27% of these patients having hiatal hernias. The onset of labor with pain and stress, coupled with the presence of opioid analgesics, are independent factors associated with a reduction in gastric emptying. Increased difficulty with intubation occurs in the parturient related to hormonally induced mucosal edema and increased breast mass. For many reasons, the parturient is at an increased risk for aspiration.3,39-41

Interestingly, however, this risk has significantly decreased since Mendelson reported a maternal death rate from aspiration during C-section of 1:667.2,5 This may well be due to the increased use of regional anesthesia, as well as the application of rapid-sequence induction (RSI) techniques, with cricoid pressure and cuffed endotracheal tubes. The use of pharmacologic interventions, although not proven to alter the incidence, may also be a contributing factor. The adoption of difficult airway practices that discourage persistent failing attempts at intubation may be an important factor, as is the increased use of regional anesthesia.

A number of recent publications support the contention that the risk of aspiration has become a much smaller contributor to maternal morbidity and mortality. Mhyre et al42 reviewed all reported maternal deaths in the state of Michigan, USA, between 1985 and 2003. Of the recorded 855 deaths over that time, 15 were felt to be associated with anesthesia in either a related or contributing form. Of the 15 cases, only 1 was felt to be due to aspiration. This occurred in the PACU following caesarian delivery of a stillbirth. The rest of the deaths had no association with aspiration. Interestingly, all anesthesia-related deaths from airway issues occurred during emergence from general anesthesia or in the recovery room. None occurred during induction.

In a recent prospective observational study, McDonnell et al43 reported on the incidence of problems associated with airway management in the parturient, during the period 2005 to 2006, in 13 hospitals with just under 50,000 deliveries per year. During that period, 1095 general anesthetics were performed. In that series, eight cases reported regurgitation (0.7%), with one case of aspiration confirmed (0.1%). Two of the regurgitation cases occurred in elective caesarian sections. Of the eight regurgitation cases, four occurred during induction, and five at emergence (one patient regurgitated at both times). Interestingly, the incidence of difficult intubation was 3.3%, with failed intubation of 0.36%. The later were managed with laryngeal mask airway (LMA).

The low incidence of aspiration is supported by the Closed Claims Analysis of the ASA44. From 1990 onward, only two cases of aspiration were implicated in a maternal death or permanent brain damage, with one of these being in association with general, the other with regional anesthesia.

In conclusion, the incidence of aspiration in obstetrics continues to decline as a source of morbidity and mortality. Increased use of regional anesthesia, a larger number of skilled practitioners comfortable with airway management options, better monitoring, and the use of prophylaxis may all be contributing factors.

5.4.3.6 Age

According to Warner,6 age was not found to be an independent risk factor for aspiration. Olsson,8 however, did find that extremes of age increased the risk of aspiration. Warner12 reviewed 63,180 anesthetics in children under the age of 18. The incidence of aspiration in that population was not dissimilar to adults, except that there was an increased incidence of aspiration in patients less than 3 years of age. Over 91% of the aspirations in this population had either a bowel obstruction or ileus perhaps skewing the incidence in young children, although there is some uncertainty as to the effectiveness of the LES in this population. Distended stomachs from both fluids and air entrained during crying or using a pacifier predisposes to gastric reflux when these infants cry or gag. The efficacy and method of application of cricoid pressure during RSI in small children has not been defined.

Borland found that the incidence of aspiration in the pediatric population was 10.2:10,000 higher than Warner's reported 3.8:10,000.12,45

5.4.3.7 Decreased Levels of Consciousness and Neurological Disease

It is recognized that the incidence of aspiration of extraglottic (eg, blood) and lower GI tract (eg, stomach contents) contaminants is increased in patients with a reduced level of consciousness.8,13 In these patient populations, loss of function of the LES and upper esophageal sphincter and delayed gastric emptying combine with a reduction of upper airway protective reflexes to promote both regurgitation and aspiration.46,47 This has relevance for the postanesthetic period as well, as it has been shown that patients left in the supine position with a reduced level of consciousness have an increased incidence of aspiration.

Patients with other underlying neurological diseases, such as Parkinson disease and multiple sclerosis, are also at increased risk of aspiration due to impairment of their protective airway reflexes.48 The diabetic with autonomic neuropathy has been demonstrated to have delayed gastric emptying, sometimes manifested by early postprandial satiety, but it is usually asymptomatic. Diabetics have a theoretically increased incidence of difficult laryngoscopy and intubation due to glycosylation of collagen in the cervical vertebrae. Inspite of speculation that diabetics ought to be at increased risk of regurgitation and aspiration,49,50 no studies have found diabetes to be an independent risk factor for aspiration.1,6-8,10-12,45

5.4.3.8 Bowel Obstruction or Other Gastrointestinal Pathology

As discussed in Section 5.4.1 in this chapter, increased gastric volume predisposes patients to an increased risk of aspiration. Gastric obstruction, and or ileus, is one of the commonest associations with aspiration.8,10,12 The incidence of aspiration in esophageal endoscopy is 1:188, and appendectomy is 1:751.

5.4.3.9 Full Stomach

Even in the absence of bowel pathology, recent ingestion of a meal has been documented to be a risk factor for aspiration.6,12 Guidelines for fasting have been developed for the elective population. However, fasting does not guarantee an empty stomach and RGVs can be quite variable.

5.4.4 Is There a Difference in Gastric Emptying in Emergency Patients or Those Who Have Received Opioids?

Trauma patients have been shown to have delayed gastric emptying up to a week after injury. Patients who are critically ill, in ICU, also have significantly delayed gastric emptying.51 Neurological injury, either head or spinal cord, is associated with significant delays in gastric emptying related, in part, to catecholamine surge.52

Opioids, irrespective of the manner of administration, have been shown to decrease gastric emptying significantly.53-55

5.5 Strategies Aimed at Minimizing Aspiration Risk

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5.5.1 What Are the Current Fasting Guidelines? What Evidence Supports Their Use?

The American Society of Anesthesiologists has published a set of fasting guidelines, generated from a review of the available literature and expert opinion.56 These guidelines were developed with the healthy patient in mind, booked for elective surgery. They are not intended to be applied to patients with comorbidities that would increase the risk of aspiration. There is a striking paucity of evidence around the relationships between fasting times, gastric volume, pH, and the risk of pulmonary aspiration. The consensus guidelines recommended the following:

For clear fluids, the Task Force recommended a minimum 2-hour period of preoperative abstinence. Clear fluids consist of water, black tea or coffee, pulp-free juices, fat-and protein-free drinks, and carbonated drinks. There is controversy as to the benefits of ingestion of carbohydrate-containing beverages. Some investigators feel that they may reduce gastric volume and raise pH, although this difference is not of clinical significance. There is some evidence to suggest that fasting itself may have detrimental effects, particularly in the pediatric population, resulting in greater anxiety and hunger.

For breast milk, the Task Force recommended a fasting period, for both infants and neonates, of 4 hours. Commercial milk and infant formula have a recommended fasting period of 6 hours.

A minimum period of 6 hours is recommended from the last ingestion of solids until the provision of anesthesia for elective surgery following a light meal. Indeed, some studies have noted that solids, particularly fats, can be found in the stomach for periods of over 8 hours after a meal. The Task Force recommended that consideration should be taken into account of the amount and type of food prior to the provision of anesthetic care after consumption of meals other that what is considered "light" (ie, clear liquids and toast).57,58

There is growing controversy as to the application of these guidelines in the parturient,59 a complex group, as there is always a potential need for emergency surgery. It would seem reasonable to allow the moderate intake of clear fluids or ice chips for the low-risk parturient. However, the high-risk parturient, either due to comorbidities or at increased risk of requiring an operative delivery, should be fasted.60 For elective cesarean sections, a fast of 8 hours following solids is recommended.

5.5.2 What Role Do Pharmacological Agents Play at Minimizing Aspiration Risk?

Although evidence exists to support the contention that pharmacological agents reduce gastric acid production, gastric volume, or both, no evidence exists to support their use in preventing or reducing the incidence of aspiration or improving outcome if aspiration was to occur. Furthermore, the administration of many of the pharmacological agents could not be justified on the basis of cost-benefit analysis. Subsequently, the ASA Task Force has not recommended the routine use of any pharmacological interventions for the prevention of aspiration.

Similarly, there are no recommendations regarding the at-risk patient, other than the use of nonparticulate antacids in the obstetrical population. The majority of studies looking at the efficacy of these drugs have been carried out in the healthy, low-risk populations.

H-2 antagonists, such as ranitidine, famotidine, and nizatidine, act by binding competitively to the histamine receptors on the gastric parietal cell. They are effective in increasing gastric pH and reducing gastric volume within 2 to 3 hours of administration. Unfortunately, the effect of the drug diminishes after a few days as tolerance develops.61

Proton pump inhibitors interfere with the H+/K+ ATPase pump on the parietal cells. They are less effective than H-2 antagonists if the intent is to use them for a single dose as they require at least two doses to be effective, both the night before and the morning of surgery. Tachyphylaxis does not develop with these agents.

Although reductions in gastric acid and volume have been shown with these agents, they do not reduce the harm from biliary fluid or particulate matter aspiration. Evidence from the animal literature suggests that pulmonary injury from bile is as significant, if not more so, than acid alone.62 Bile, with a pH of 7.19, caused severe chemical pneumonitis and edema in one animal study.62

Prokinetic agents are used to accelerate emptying of the stomach, thereby reducing RGV. The most commonly used of these is metoclopramide. It has multiple effects, including prokinetic properties, antiemetic properties, and finally, an effect on increasing the tone of the LES. It acts by antagonizing dopamine and serotonin receptors. Depending on the receptor subtype, it may also act as an agonist. Its antiemetic effects are largely due to the 5HT3 antagonism and the prokinetic effects from the 5HT4 agonism. Its prokinetic properties, however, are quickly inhibited by the presence of opioids and anticholinergic agents.

Of interest, the antibiotic erythromycin has been shown to be an effective agent in stimulating gastric motility, thereby increasing the rate of gastric emptying. It exerts its effect via the motilin receptor. Unlike metoclopramide, it has no extrapyramidal side effects and its prokinetic properties are not inhibited by opioids or anticholinergics. Doses of 1 to 2 mg·kg−1 have been reported to be effective in reducing gastric fluid volume.63,64

The use of antacids has been demonstrated to reduce the pH of gastric contents for variable lengths of time. As discussed earlier in this chapter, the administration of particulate antacids can be problematic. The use of clear nonparticulate antacids has been in wide use for more than two decades, primarily in the obstetrical population. Sodium citrate is in routine use, prior to elective or emergency obstetrical procedures. Bicitra is a commercially available form of sodium citrate. The mechanism of action is by conversion to sodium bicarbonate. Rebound acidity will occur with prolonged use, increasing the volume of acid production.65

5.5.3 What Is the Role of Rapid-Sequence Induction?

Rapid-sequence induction with cricoid pressure has been described as the standard of care in anesthesia for patients at risk for gastric regurgitation.66 As well, it is cited to be the most common method of airway management by emergency physicians for critically ill and injured emergency patients. It is characterized by a high success rate and a low rate of serious complications.18,67,68 RSI is also the principal salvage technique when other oral or nasal intubation methods fail in the emergency department.8

The use of a rapid-sequence technique results in fewer attempts, more rapid intubations, and higher success rates when compared to intubation with no sedation or sedation alone, both in hospital and in the prehospital setting.69-71 Concerns about the role of rapid- sequence techniques in the prehospital setting for the care of severely head-injured patients relate to the potential for hypoxemia under some circumstances. The major issues seem to be the occurrence of severe hypoxia during induction in patients who were not hypoxic before induction and the excess morbidity and mortality in those patients. An effective strategy for maintenance of oxygenation is needed before it can be concluded that rapid-sequence intubation is of value in the out-of-hospital care of patients with serious closed head injury.72,73

5.5.4 Describe the Technique of RSI

The patient should be placed at a height that is most convenient for the airway practitioner performing laryngoscopy. The head should be placed in the "sniffing" position with a firm pillow under the occiput. Although the benefit of the sniffing position compared to simple extension was recently challenged by Adnet, it did provide an advantage in patients who were obese or in whom there was at least one factor predictive of difficult intubation.74

5.5.4.1 Denitrogenation

The usual method for denitrogenating patients involves having the patient breathe 100% oxygen at tidal volumes through a snug-fitting facemask for 3 to 5 minutes. An alternative strategy is to have patients take four vital capacity breaths, but there is evidence that the former methodology is preferable.75 Having said that, a recent review has concluded that having the patient take eight deep breaths (8DB) in 60 seconds provides a similar duration of safe apnea as does 3 to 5 minutes of tidal volume ventilation.76 For this reason, whenever possible, it is recommended that either the tidal-volume breathing or the 8DB technique be employed. The same review concluded that denitrogenation of obese patients in the head-up compared to supine position also provided a longer period of safe apnea after the induction of anesthesia.

5.5.4.2 Cricoid Pressure

The cricoid cartilage should be identified by the assistant during denitrogenation, before induction of anesthesia, and the accuracy of the landmark should be confirmed by the airway practitioner. Cricoid pressure may be gently applied at the start of the induction sequence and the pressure increased to the amount recommended concurrent with the induction of anesthesia. The pressure should not be released until the cuff is inflated and the intratracheal position of the tube has been confirmed.

5.5.4.3 Nasogastric Tubes and Gastric Evacuation

Sellick recommended evacuating the stomach with a gastric tube and then removing the tube before induction of anesthesia.4 Stept77 argued that there was little evidence to support an effect of the tube on esophageal sphincter competence and suggested that the risk would be outweighed by the advantage of continuous gastric decompression when the tube was left in situ. Satiani et al78 demonstrated no difference in the incidence of regurgitation with or without a nasogastric tube. Salem and colleagues demonstrated the effectiveness of cricoid pressure in preventing reflux in both infant and adult cadavers with nasogastric tubes in place.79 It is recommended that a nasogastric tube be used to empty the stomach and then be left open to atmosphere to limit increases in intra-gastric pressure during induction of anesthesia.

5.5.4.4 Sedatives/Hypnotics during RSI

Despite wide acceptance and use of RSI, no single agent has emerged as the drug of choice for sedation and hypnosis during RSI. A deeper plane of anesthesia may improve intubating conditions in emergency patients undergoing RSI by complementing incomplete muscle paralysis.80

The use of etomidate, ketamine, a benzodiazepine, or no sedative agent prior to neuromuscular blockade is associated with a lower likelihood of successful intubation on the first attempt, as compared with thiopental, methohexital, or propofol.80 The use of the benzodiazepine midazolam alone is associated with a prolonged delay to time of laryngoscopy, and doses greater than 0.1 mg·kg−1 are associated with a dose-related incidence of hypotension.80-83

Etomidate, thiopental, and propofol have a favorable effect on intraocular pressure (IOP) and intracranial pressure (ICP).84-86 Barbiturates provide cerebral protective qualities against ischemia caused by elevated ICP. However, barbiturates may significantly lower mean arterial blood pressure and thereby lower cerebral perfusion pressure, potentially compromising collateral blood flow to ischemic regions of the brain.84 Although propofol also reduces ICP, it reduces mean arterial pressure (MAP) more than barbiturates and can thus cause a significant reduction of cerebral perfusion pressure.87 Etomidate, in contrast to barbiturates and propofol, reduces ICP to a similar degree while maintaining or increasing MAP and cerebral perfusion pressure, but there is evidence of neurotoxicity in experimental models.88,89

Ketamine, when used in the presence of hypovolemic shock, can be unpredictable in its effect on the hemodynamic profile. It possesses both indirect sympathomimetic stimulation and direct myocardial depressant properties, which support or raise systemic blood pressure in the acutely injured and hypovolemic patient. However, a patient who has been physiologically stressed for an extended period may be depleted of endogenous catecholamines, thereby rendering indirect autonomic stimulation ineffective and allowing the direct myocardial depressant effects to dominate.

Although it clearly has some advantages in a compromised patient, a significant disadvantage of etomidate is that it does not blunt the sympathetic response to endotracheal intubation.90 This may result in hypertension and tachycardia during endotracheal intubation secondary to sympathetic stimulation. This response may raise ICP and increase myocardial work. Mitigation of this effect is achieved with the use of 1.5 to 5 μg·kg−1 of fentanyl in conjunction with etomidate.91

Lidocaine is widely used as a pretreatment agent to decrease the magnitude of increase of ICP in patients with closed head injury (with or without increased ICP). In fact, the evidence that IV lidocaine reduces the magnitude of the increase in ICP with elective tracheal intubation or suctioning in patients with increased ICP is indirect, and there is no evidence that it renders this effect in head-injured patients undergoing RSI.92

5.5.4.5 the Choice of Muscle Relaxant during Rapid-Sequence Techniques

Succinylcholine is widely used in anesthesia and emergency medicine during rapid-sequence techniques. Doses approximating 1 mg·kg−1 have been conventionally used for intubation; the average time to return to 50% of twitch height following this dose is 8 to 9 minutes, and 10 to 11 minutes for a return to 90% twitch height. A number of authors have explored the use of smaller doses to decrease the time to recovery and to limit the dose-dependent sequelae. El-Orbany93 assessed onset times and time to twitch recovery for succinylcholine in doses of 0.3, 0.4, 0.5, 0.6, and 1 mg·kg−1 after anesthesia was induced with fentanyl and propofol. Onset times ranged between 82 and 52 seconds, decreasing with increasing doses of succinylcholine but not differing between 0.6 and 1 mg·kg−1. Intubation conditions were often unacceptable after 0.3 and 0.4 mg·kg−1 doses, but acceptable conditions were achieved in all patients receiving more than 0.5 mg·kg−1; intubation conditions in patients receiving 0.6 and 1.0 mg·kg−1 were identical. The times to twitch recovery and to regular spontaneous reservoir bag movements were significantly shorter in the 0.6 mg·kg−1 dose group compared with patients receiving 1 mg·kg−1. Naguib94 carried out a similar study administering succinylcholine 0.3 to 1.0 mg·kg−1 after anesthesia was induced with fentanyl and propofol. Intubating conditions were acceptable (excellent plus good grade combined) in 30%, 92%, 94%, and 98% of patients after 0.0, 0.3, 0.5, and 1.0 mg·kg−1 succinylcholine, respectively. The calculated doses of succinylcholine that were required to achieve acceptable intubating conditions in 90% and 95% of patients at 60 seconds were 0.24 mg·kg−1 and 0.56 mg·kg−1, respectively.

While these results may have significant clinical implications, more studies are needed to examine the effectiveness of these smaller doses of succinylcholine in different patient populations, including obese, pregnant, pediatric, trauma, and critically ill patients. It must also be emphasized that the goal is "100% acceptable intubating conditions," particularly in an emergency.

There is considerable enthusiasm in anesthesia practice to replace succinylcholine with a nondepolarizing muscle relaxant. At this time, rocuronium has emerged as the most likely nondepolarizer to fill this role. Rocuronium 1 mg·kg−1 given after induction in a rapid-sequence technique is clinically equivalent to succinylcholine 1 mg·kg−1.95 The incidences of clinically acceptable intubating conditions with rocuronium and succinylcholine were 93.2% and 97.1%, respectively. Clinically acceptable conditions occurred less frequently when rocuronium 0.6 mg·kg−1 was used. The use of propofol 2.5 mg·kg−1 combined with rocuronium 0.6 mg·kg−1 results in satisfactory intubating conditions in 90% of patients within 61 seconds (range 50-81 seconds).96 The use of either thiopental (5.0 mg·kg−1) or etomidate (0.3 mg·kg−1) combined with rocuronium 0.6 mg·kg−1 results in a longer time to achieve, as well as a lower incidence of satisfactory intubating conditions than that achieved with propofol/rocuronium combinations.97 The addition of alfentanil 10 μg·kg−1 to these doses of etomidate and thiopental results in an increased likelihood of acceptable intubation conditions at 60 seconds following rocuronium administration.98

A recent review has concluded that a dose of succinylcholine of greater than 1 mg·kg−1 is required to ensure excellent intubating conditions and that smaller doses may not consistently provide such conditions.76 Rocuronium 1 mg·kg−1 is a suitable alternative to succinylcholine during RSI, and although it will provide acceptable intubation conditions as often as equivalent doses of succinylcholine, it will provide excellent conditions less often. The time to full twitch recovery following paralyzing doses of rocuronium may be in excess of 1 hour, a factor that may exceed the comfort level of some practitioners. The availability and use of Sugammadex would be a potential solution in the situation where rocuronium is required for rapid-sequence induction, rather than succinylcholine as concern exists due to the prolonged neuromuscular block from the dose of rocuronium required.99

5.5.4.6 Positive Pressure Ventilation during RSI

In the 18th century, application of pressure in the cricoid area was advocated to allow for ventilation of the lungs without causing gastric distention.100 Sellick,4 in his description of cricoid pressure, also recommended ventilating the lungs while awaiting onset of muscle paralysis. On the other hand, Stept et al recommended against the use of ventilation after application of cricoid pressure77 and conventional practice has favored this recommendation. However, there is now evidence that not only is there a benefit to ventilating the patient's lungs during the period of apnea but also that it can be done safely.

The average time to return to 90% of twitch height following an intubating dose of succinylcholine is considerably longer than it will take most patients to desaturate, even under ideal circumstances.101 Using a simulator model, Hardman et al have identified the factors that shorten the time to desaturate with apnea.102 The factors that have a moderate effect are a reduced ventilatory minute volume preceding apnea and a reduced duration of denitrogenation. Those that have a large effect are increased oxygen consumption and reduced functional residual capacity. All of those factors are likely to be relevant in many instances of RSI.

There is a relationship between airway pressure and gastric inflation.103,104 In subjects ventilated by bag-mask without cricoid pressure, airway pressures below 15 cm H2O rarely cause stomach inflation. Pressures between 15 and 25 cm H2O will result in gastric insufflation in some patients, and pressures greater than 25 cm H2O do so in most patients.103 Application of cricoid pressure during BMV increases the maximum pressure that may be generated during mask-ventilation, without air entering the stomach, to about 45 cm H2O.104

Petito and Russell measured the ability of cricoid pressure to prevent gastric inflation during BMV of the lungs.105 Fifty patients were randomized to either have or not have cricoid pressure applied during a 3-minute period of standardized mask-ventilation. Patients who had cricoid pressure applied had less gas in the stomach after mask-ventilation. However, more patients who had cricoid pressure applied (36% vs 12%) were considered more difficult to ventilate and these patients tended to have more air in the stomach than those patients considered easy to ventilate with applied cricoid pressure.

In summary, the application of cricoid pressure significantly reduces the volume of air entering the stomach at low to moderate ventilation pressures. It allows for continued ventilation of the lungs even in situations where past convention would have discouraged it, such as in RSI. Ventilating the lungs while awaiting the onset of muscle block would clearly be a useful maneuver to prevent oxygen desaturation, and there is an evidence base that supports this intervention. In order to prevent gastric insufflation, every effort should be made to ventilate the lungs at the lowest pressure possible.

5.6 Cricoid Pressure

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5.6.1 Discuss the Applied Anatomy of Cricoid Pressure

The cricoid cartilage is shaped like a signet ring with the narrow part of the ring being oriented anteriorly. The anterior arch of the cricoid cartilage is attached to the thyroid cartilage by the cricothyroid membrane. Laterally the cricothyroid muscles are situated in the cricothyroid gap (see Figure 3-23). The inferior horns of the thyroid cartilage articulate with the lateral surfaces of the cricoid cartilage. The cricoid cartilage is attached to the first tracheal ring by the cricotracheal ligament. The esophagus begins at the lower border of the posterior aspect of the cricoid cartilage. Sellick proposed the application of cricoid pressure during induction of anesthesia, to prevent regurgitation of gastric or esophageal contents by compressing the esophagus between the cricoid and the cervical spine, obliterating the esophageal lumen.4 To perform the maneuver, the neck was extended, increasing the anterior convexity of the cervical spine and stretching the esophagus. Sellick hypothesized that this prevented lateral displacement of the esophagus when cricoid pressure was applied. However, Vanner106 reported that contrast CT scanning in one patient revealed that when cricoid pressure was applied, although the cricoid cartilage and cervical vertebrae were approximated, only part of the esophageal lumen was obliterated. There was also slight lateral movement of the cricoid cartilage, which allowed the nonobliterated lumen to be pressed against the body of the longus colli muscle adjacent to the vertebral body. Smith107 reviewed 51 cervical CT scans of normal patients to assess the anatomic relationships between the cricoid cartilage and the esophagus. Lateral esophageal displacement relative to the cricoid cartilage was evident in half (25 of 51) of the patients; 64% of those with lateral displacement had esophageal displacement beyond the lateral border of the cricoid cartilage. Smith subsequently reported on MRI taken of 22 volunteers with and without cricoid pressure applied. The esophagus was again seen to be displaced laterally relative to the cricoid cartilage in 52.6% of the subjects; this increased to 90.5% with the application of cricoid pressure. Lateral laryngeal displacement and airway compression were observed in 66.7% and 81% of the necks, respectively, with the application of cricoid pressure.108 In neither study by Smith were the patients placed in the tonsillectomy position as recommended by Sellick. However, there is no evidence that doing so would have resulted in different findings than those reported.

The potential for lateral positioning and displacement of the esophagus relative to the cricoid cartilage possibly explains a number of case reports where, despite seemingly appropriate application of cricoid pressure during RSI, regurgitation and aspiration occurred.

5.6.2 What Is the Sellick Technique?

Sellick109 outlined a number of steps in his original description of cricoid pressure applied concurrent with anesthetic induction. The patient was placed in the tonsillectomy position with the cervical spine in extension. Before induction of anesthesia, the cricoid was palpated and lightly held between the thumb and index finger; as induction commenced, pressure was exerted on the cricoid cartilage mainly by the index finger. As the patient lost consciousness, Sellick recommended firm pressure sufficient to seal the esophagus. Cricoid pressure was initially felt to be contraindicated by Sellick in the setting of active vomiting, in the belief that the esophagus may be damaged by vomit under high pressure. He later modified this stand, stating that he felt the risk of rupture to be almost nonexistent.109 Since his original description, the technique has been exposed to much study and critique. Data have now accumulated to provide evidence to support many of Sellick recommendations.

5.6.3 Does Cricoid Pressure Reliably Protect Against Regurgitation and Aspiration?

There are no outcome studies confirming the clinical benefit of cricoid pressure when used either in anesthesia or resuscitation. Brimacombe cites numerous case reports documenting the occurrence of aspiration despite the application of cricoid pressure.66 There are also multiple studies documenting a negative impact of cricoid pressure on patient interventions, usually relating to airway management. There is also a single case report in the literature attributing rupture of the esophagus to cricoid pressure.110 It involved an elderly female subjected to laparotomy after repeated episodes of hematemesis. The patient, who vomited on induction, was positioned laterally, cricoid pressure was released, and the trachea was intubated after pharyngeal suctioning. At surgery, a longitudinal split was found in the lower esophagus. It was concluded, by the reporting authors, that the esophageal rupture represented an esophageal injury attributable to the cricoid pressure. However, the diagnosis of rupture of the esophagus as a result of the repeated episodes of hematemesis represents as likely a diagnosis, as the stomach adjacent to the area of esophageal injury was noted to be bruised and swollen during the surgery, suggesting a temporally more remote injury.

There are a number of factors that would explain why cricoid pressure cannot provide absolute protection against aspiration, in addition to the anatomic factors already outlined. The landmarks on the patient's neck may not be identified properly and, as a result, pressure not exerted on the cricoid cartilage itself. Cricoid pressure may not have been commenced prior to induction, allowing for an interval between loss of consciousness and application of pressure, during which the patient is at risk for aspiration. Personnel may be inadequately trained. Cricoid pressure may be released inadvertently before the trachea is intubated and the cuff inflated. Finally, it may be difficult to maintain occlusive pressures for prolonged periods and the maneuver may become less effective in preventing aspiration during instances of difficult intubation.

There is a paucity of data to evaluate the role of cricoid pressure in preventing patient complications. Despite the lack of conclusive evidence supporting the role of cricoid pressure in the emergency management of the airway in the setting of a full stomach, the absence of evidence of an effect does not prove that there is no benefit to the intervention. It is likely to continue to be encouraged as a pattern of practice.

5.6.4 How Much Cricoid Pressure Is Needed to Prevent Gastric Regurgitation?

Twenty newtons of applied cricoid pressure is probably adequate in many instances and 30 N is more than enough to prevent regurgitation into the pharynx in most patients. Pressures of greater than 30 N (approximately 3 kg, or 7 lb) are unlikely to be necessary.37,111-113 The originally described forces (40 N) would rarely be necessary to prevent gastric regurgitation.

5.6.5 How Do You Measure the Performance of Cricoid Pressure?

Meek investigated the cricoid pressure technique of anesthetic assistants.114 A large variation in the force applied (from <10 N to >90 N) was observed. Performance was improved markedly by providing simple instruction and further improved by practical training in the application of target force on a simulator. Meek also studied six operating room assistants performing simulated cricoid pressure (on a model of the larynx) to determine how long and under what conditions cricoid pressure could be sustained.115 Subjects were asked to maintain forces of 20, 30, and 40 N for a target time of 20 minutes, with the arm either extended or flexed; most could not do so. Mean times to release of cricoid pressure varied from 3.7 minutes (flexed) to 7.6 minutes (extended) at 40 N, to 6.4 to 10.2 minutes at 30 N, and 13.2 to 14.6 minutes at 20 N, respectively. These findings suggest that the ability to generate forces sufficient to provide esophageal occlusion and airway protection is limited.

5.6.6 Is Bimanual Cricoid Pressure Better Than a One-Handed Technique?

Flexion of the head on the neck may occur as a result of cricoid pressure and this may impede laryngoscopy. Bimanual (two-handed) cricoid pressure with the free hand of the assistant placed behind and supporting the neck or alternatively, with the use of a small support placed behind the patient's neck, has been recommended to overcome the tendency to neck flexion.116 However, Vanner found no benefit for laryngoscopy when a cushion was placed behind the neck to prevent neck flexion during the application of cricoid pressure.117 Cook compared the view of the larynx at laryngoscopy in 121 patients with one- or two-handed cricoid pressure applied.118 In 28 cases the laryngeal view was better with one-handed cricoid pressure, and in 11 cases the laryngeal view was better with two-handed cricoid pressure. In 81 cases, the view was unaffected by the type of cricoid pressure applied. Two-handed cricoid pressure was not demonstrated to routinely provide an advantage over the one-handed technique.

Yentis119 also studied the effect of the two different methods of cricoid pressure on laryngoscopic view in 94 patients and reached contrary conclusions to those of Cook. In 21 cases, a better laryngoscopic view was obtained with the bimanual technique; in 8 cases it was better with the single-handed technique; and in 65 cases the method of cricoid pressure made no difference. The force applied may have some impact on both the amount of neck flexion and the balancing potential of a bimanual technique. In the study by Yentis, considerably larger forces were applied (50-55 N) than in either Vanner's (30 N) or Cook's (40 N) studies. It is possible that more neck flexion occurred with the larger applied force and more benefit was thus realized when a bimanual technique was employed.

In summary, the technique of cricoid pressure which produces the best laryngoscopic view in an individual patient cannot be predicted. However, an alternative technique should be considered if it is suspected that the technique of cricoid pressure application is having a deleterious effect on direct laryngoscopy.

5.6.7 Does It Matter Which Hand Is Used to Apply Cricoid Pressure?

Cook assessed the cricoid force applied by trained anesthesia assistants, as well as the ability to maintain the applied force, and compared the two hands.120 Overall, the assistants applied a lower force than is classically taught but were able to maintain the force with either hand for a sustained period. The use of the left hand resulted in slightly lower applied forces but the differences were not felt to be clinically relevant. Thus, no recommendation can be made regarding position of the assistants as it relates to the handedness of the cricoid pressure.

5.6.8 How Does Cricoid Pressure Affect Ventilation and Airway Interventions?

A concern about cricoid pressure in general, and at higher applied pressures in particular, has been the potential for compromise of either the quality of the airway or the effectiveness of airway interventions.121-123 In a recent report of 23 failed intubations over a 17-year period in one maternity unit, cricoid pressure was maintained during the failed intubation drill.124 In 14 patients (60%), ventilation via a facemask was not difficult, indicating that cricoid pressure was at least not harmful in these patients. In the remaining nine patients, ventilation was difficult in seven patients (30%) and impossible in two (9%). Although some patients had laryngeal edema, it is possible that cricoid pressure contributed to the difficult ventilation in these patients.121

Vanner123 reported that difficulty in breathing occurred in about half of awake patients with 40 N forces applied, and Lawes125 reported that airway obstruction occurred in about 10%. Hartsilver and Vanner investigated whether airway obstruction is related strictly to the force applied or whether the technique of application was also relevant.126 They recorded expired tidal volumes and inflation pressures during mask-ventilation in anesthetized patients. Airway obstruction occurred in 2% of patients with pressure applied at 30 N, and in 35% with 44 N. If the force is applied in an upward and backward direction, obstruction at 30 N occurs in 56%.

Aoyama assessed the effect of cricoid pressure (prior to insertion) on the positioning of and ventilation through the laryngeal mask airway (LMA).127 Ventilation was considered adequate in all patients in the group with no cricoid pressure applied but in only 25% of those with pressure applied. The glottis was visible fiberoptically below the mask aperture in all patients when no pressure was applied, suggesting correct placement. Correct placement was evident in only 15% of patients who had the LMA placed with cricoid pressure applied. Fiberoptic evaluation showed that the mask was not inserted far enough in the remaining 85% of patients. Radiographs taken showed that the tip of the mask in the no-cricoid-pressure group was located below the level of the cricoid cartilage (C6 or C7 vertebra), whereas the mask tip in the cricoid pressure group was above this level (C4 or C5).

Asai128 studied 50 patients to assess if the cricoid pressure applied after placement of the laryngeal mask prevented gastric insufflation, without affecting ventilation. Cricoid pressure significantly decreased mean expiratory volume delivered through an LMA. This inhibitory effect was greater when the pressure was applied without support of the neck. Cricoid pressure also reduced the incidence of gastric insufflation. In no patient was the mask dislodged. The inhibitory effect of cricoid pressure on ventilation without support of the neck was greater than cricoid pressure with support of the neck.

MacG Palmer and Ball129 studied the effect of cricoid pressure on airway anatomy in 30 anesthetized patients examined fiberoptically through an LMA. They assessed the effect of 20, 30, and 44 N on the internal appearance of the cricoid and vocal cords. At 44 N, cricoid deformation occurred in 90% of patients and 50% had cricoid occlusion; 43% had cricoid occlusion at 30 N and 23% at 20 N. Associated difficulty in ventilation was present in 50% of patients and 60% had vocal cord closure with associated difficult ventilation, at forces up to 44 N.130-132

Smith and Boyer evaluated the ease of rigid fiberoptic (WuScope System™) intubation in anesthetized adults receiving cricoid pressure.133 Each patient had their trachea intubated under two conditions: with and without cricoid pressure. An easy intubation occurred in 91% of patients without cricoid pressure and in 66% of patients with cricoid pressure applied. Cricoid pressure compressed the vocal cords in 27% of patients and impeded tracheal tube placement in 15%. In three patients (9%), pressure had to be released in order to successfully intubate their tracheas.

Hodgson134 assessed the effect of application of cricoid pressure on the success of lightwand intubation in 60 adult female patients presenting for abdominal hysterectomy. All 30 patients allocated to intubation without cricoid pressure were intubated successfully, at the first attempt, within a median time of 28 seconds. Lightwand intubation with cricoid pressure was successful in 26 of 30 patients at the first attempt, but the median time to successful intubation was significantly longer at 48.5 seconds. Three patients required two attempts for successful intubation and one could not be intubated with the lightwand while cricoid pressure was applied.

Shulman compared the Bullard laryngoscope (BL) with the flexible bronchoscope (FB) in a cervical spine injury model. Using in-line stabilization with or without cricoid pressure, he concluded that BL is more reliable when used in the setting of in-line stabilization with cricoid pressure applied. He determined as well that BL is also quicker and more resistant to the effect of cricoid pressure than is FB.135

In summary, properly applied cricoid pressure has a limited impact on the ability to ventilate the lungs, the quality of the airway realized, and the effectiveness of airway interventions. However, as applied pressures are increased, the potential for compromise of both the airway and airway interventions is also increased.

5.6.9 What Is the Impact of Cricoid Pressure on Cervical Spine Movement?

In the setting of potential or actual cervical injury, concerns have been expressed that the application of cricoid pressure may result in cervical spine displacement, causing or worsening cord injury. Although cricoid pressure is widely used during airway management in trauma settings, there are no data either affirming its safety or implying that it actually poses a risk. Gabbott136 assessed the impact of single-handed cricoid pressure applied concurrent with manual in-line stabilization of the neck in a neutral position in 30 healthy patients undergoing general anesthesia with neuromuscular paralysis. Vertical displacement was measured from the midpoint of the neck (directly below the cricoid cartilage), and mean neck displacement (vertebral) was 4.6 mm with a range of 0 to 8 mm.

Gabbott then measured the effect of single-handed cricoid pressure on cervical spine movement after applying manual in-line stabilization in cadavers.137 The median vertical displacement measured from the body of C5 was 0.5 mm (range 0 to 1.5 mm). There was no disruption of the lines formed by the anterior or posterior borders of the cervical bodies. In this second study, Gabbott was unable to demonstrate that single-handed cricoid pressure caused clinically significant displacement of the cervical spine in a cadaver model.136

Wood138 studied the effect of cricoid pressure on the view obtained at laryngoscopy with concurrent cervical stabilization maneuvers. Laryngoscopic view was best in the unrestrained position, with 77.4% of these views being Grade 1. More frequently, Grade 3 views were obtained in the presence of cervical stabilization with or without cricoid pressure. When in the stabilized position, application of cricoid pressure improved the view in 26% of patients. Wood concluded that cricoid pressure may actually improve the view of the larynx when the neck is stabilized even though it is often detrimental to the view in the absence of stabilization.

In summary, there is no evidence which would either encourage or discourage the use of cricoid pressure in the setting of real or potential cervical injury. However, its use in this setting is common and there is no evidence of harm caused. Cricoid pressure may actually facilitate laryngoscopy when cervical immobilization is employed, in much the same fashion that anterior laryngeal pressure does.

5.7 Other Considerations

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5.7.1 What Is the Aspiration Risk Associated with the Use of Extraglottic Devices?

When discussing extraglottic devices, the focus is generally on the LMA and its various forms. Other devices are available such as the laryngeal tube. However, the vast majority of the literature relates to the LMA.

The LMA has enjoyed over a decade of widespread use in anesthesia worldwide and has been hailed for its ease of use, efficacy, and low incidence of complications. As its use expanded, so did the nature of its application and it began to be employed for positive pressure ventilation, prolonged anesthesia (more than 2 hours duration), laparoscopic and nonlaparoscopic abdominopelvic surgery, and for surgery in the prone position. These applications have been labeled nonconventional applications and as these patterns of practice have become more common, increasing concerns about aspiration are being expressed.

Authors have addressed these concerns in three ways:

(1) Esophageal pH probes have been employed to determine the incidence and extent of GER during anesthesia with LMAs in place.
(2) Deliberate pharyngeal soiling has been used to measure the protection afforded to the respiratory tract by the LMA. Clinical studies have compared the incidence of reflux when the LMA was employed relative to endotracheal tubes or alternate airways.
(3) Finally, retrospective series and case reports have been presented to both estimate the incidence of aspiration associated with LMA and detail the clinical events and sequelae when aspiration occurred. The bulk of the published literature refers to the LMA Classic™ but more recently, literature relating to the newer iterations of the LMA, including the LMA ProSeal™ (PLMA) and the intubating LMA, has appeared.

Roux et al139 studied esophageal reflux, using esophageal pH probes, in 60 patients administered anesthesia with either a face-mask or an LMA. They concluded that the use of the LMA was associated with an increased incidence of gastric reflux in the lower esophagus, but not mid-esophagus, and that reflux was not influenced by either volume of air or pressure inside the LMA cuff. Joshi et al140 found no evidence of hypopharyngeal aspiration using pH probes in a study that compared the LMA with the endotracheal tube in spontaneously breathing patients. Ho et al141 reported that the use of positive pressure ventilation in a similar setting did not increase the risk of reflux. Hagberg et al142 studied both reflux and tracheal aspiration using pH electrodes measuring in both the proximal and distal esophagus, as well as the trachea. The patients were managed with either an LMA or a Combitube™. No changes in esophageal or pharyngeal pH were observed, but 12% of the LMA group and 4% of the Combitube™' group had pH changes at the tracheal level. No patient demonstrated clinical signs or symptoms of aspiration.

Using pH probes, McCrory and McShane143 determined the incidence and level of reflux during spontaneous respiration with the LMA and compared the supine and lithotomy positions. The pH was measured in both the esophagus and the bowl of the LMA. Esophageal reflux occurred in 38% of the patients in the supine position and 100% of the patients in the lithotomy position. A change in pH was also measured in the bowl of the LMA in 57% of patients in the lithotomy position, but was not seen in the supine position.

Cheong et al144 compared the incidence of reflux and regurgitation in adults associated with LMA removal and compared the incidence when two strategies were employed for removal. In one group, the LMA was removed when signs of rejection were observed (swallowing, struggling, restlessness) and in the second, when the patients could open their mouth to command. A pH probe was used to assess reflux and a gelatin capsule containing methylene blue, swallowed before anesthesia induction, was employed to identify regurgitation. Instances of reflux measured with the pH probe were more common in the late-removal group. There were no regurgitation events observed in either group.

Evans et al145 assessed the ability of the LMA ProSeal™ to isolate the respiratory tract from the digestive tract. Methylene blue-dyed saline was instilled into the hypopharynx via the drainage tube once the mask was in place in 102 patients. A flexible bronchoscope was used to view the bowl of the mask to assess for evidence of methylene blue. Although an effective barrier was observed in all patients initially, mask displacement occurred in two patients (2%) and dye leaked into the bowl of the mask.

Verghese and Brimacombe146 surveyed the use of the LMA in 11,910 patients, with special emphasis on nonconventional use of the LMA, and the occurrence of airway-related complications. Of the 11,910 uses recorded, 2222 were considered to be nonconventional. Eighteen of the 44 documented critical incidents related to the airway including laryngospasm (8), regurgitation (4), bronchospasm (3), vomiting (2), and aspiration (1). There was no difference between the rates of occurrence of critical incidents in conventional (0.16%) versus nonconventional (0.14%) use of the LMA. Brimacombe and Berry147 performed a meta-analysis of the published literature relevant to the association of LMA use and aspiration. In the reviewed papers, there were three cases of aspiration in 12,901 patients, with no death or permanent disabilities recorded.

Keller et al148 described three cases of aspiration: the first death and the first case of severe permanent neurological injury was associated with aspiration and the use of the LMA. All three patients were considered by the authors to be at increased risk of aspiration; two had previous gastric surgery and the third had a hiatus hernia. Keller also reported a literature review designed to assess risk factors for LMA-associated aspiration. Twenty case reports were identified in the literature. In 14 cases, there were factors that could increase the risk of aspiration, including inadequate depth of anesthesia (7), intra-abdominal surgery (3), upper GI tract disease (2), lithotomy position (2), exchanging the LMA (2), a full stomach (1), multiple trauma (1), multiple insertion attempts (1), obesity (1), opioid use (1), and cuff deflation (1).

In summary, there is evidence that gastric reflux into the lower esophagus occurs with some frequency during anesthesia provided with an LMA even in healthy patients without obvious risk factors. Reflux to higher levels of the esophagus or into the pharynx appears to be less common but does occur. It may be increased by patient positioning, such as the lithotomy and lateral decubitus positions. Although the LMA cuff may provide somewhat a protective barrier to refluxing materials, the barrier is not absolute and aspiration may occur even with a PLMA in place. The incidence of aspiration associated with LMA use seems low and not significantly altered when the LMA is used in an unconventional manner. However, it is likely that many cases of LMA-associated aspirations have occurred and gone unreported. When aspirations are reported, it is common that factors traditionally associated with a higher risk of aspiration are present.

In the opinion of the authors, in situations suggesting that the patient is at an increased or high risk of aspiration, it would seem prudent to electively employ alternate methods to the LMA when managing the airway.

5.7.2 Is It Safe to Use a Lightwand Intubation Technique (Eg, Trachlight™) in Patients at Risk of Aspiration?

The Trachlight™ represents an alternate airway device that has proven its efficacy in many clinical situations. Studies have shown that it is both safe and effective, with minimal trauma and its ability to secure the airway in clinical situations where anatomical features make the use of the laryngoscope less likely to be successful. Indeed, features that predict difficult laryngoscopy have little or no correlation with the ease or difficulty of Trachlight™ intubation.149

The question of the safety of the Trachlight™ in the patient at risk of aspiration is one not well addressed in the literature. Only one paper134 exists which reviews the use of the Trachlight™ in the presence of cricoid pressure and RSI in a randomized trial and it suggests that the use of the Trachlight™ is hampered by the presence of cricoid pressure. Sixty healthy patients were randomized into a cricoid pressure group and a noncricoid pressure group. Of the noncricoid pressure group, there was a 100% success rate on the first attempt. In the cricoid pressure group of 30 patients, only 26 were intubated on the first attempt, three on the second, and one failed with the Trachlight™. The conclusion was that the Trachlight™ should not be used as a first-line choice for RSI.

As discussed earlier, a failed or difficult intubation increases the risk of aspiration. Under circumstances where a difficult laryngoscopic intubation is predicted, one could argue that the use of the Trachlight™ might represent a safer choice. Hung et al149 documented that the success of the Trachlight™ was at least as good, if not better than, as the laryngoscope in a series of 950 patients randomized into Trachlight™ and laryngoscope intubation. In another study, Hung et al150 studied 265 patients deemed to be difficult laryngoscopic intubations. Of these, 206 were felt to be difficult either because of previously documented problems or anatomical factors predicting difficulty, such as cervical fusion, small mandibles, and impaired mouth opening. The remaining 59 were unanticipated failed laryngoscopic intubations whose airways were secured with the Trachlight™. A total of two failures occurred, both of which could have been predicted due to anatomical abnormalities that made the transillumination difficult.

Clearly, clinical judgment is required. The patient with a full stomach from a recent meal does not have the same risk of aspirating as the patient with an acute bowel obstruction. In addition, coughing and gagging in relation to prolonged attempts at laryngoscopy are as likely, if not more so, to expose the patient to the potential of aspirating than if the assistant releases cricoid pressure momentarily to facilitate insertion of a Trachlight™.

Unfortunately, apart from the solitary paper cited above, there is not enough evidence to draw a firm conclusion.

5.7.3 Is Awake Intubation with an Anesthetized Airway Associated with a Lower Risk of Aspiration Than under Anesthesia?

Airway anesthesia is routinely used for awake intubation. Many sources caution against these airway anesthesia techniques in the patient with a full stomach, fearing that anesthetizing the upper airway impairs the cough reflex, leaving the patient at risk should regurgitation occur.151-154 The question then arises how should one proceed in a patient who has an anticipated difficult airway in the presence of elevated risk of regurgitation? Only one relevant study152 has been published in 1989. The tracheas of 123 patients at high risk for aspiration were intubated awake, but sedated, with an FB. In 114 cases, the vocal cords were anesthetized by either injection of 4% lidocaine through the working channel of the bronchoscope or by transtracheal injection of lidocaine. No local anesthetics were used on 15 occasions. Topical anesthesia was applied to the oropharynx by benzocaine–amethocaine (Cetacaine) spray and benzocaine ointment for oral intubations. Patients having nasal intubations received topical 4% cocaine to the nasal mucosa. No incidences of aspiration were identified in this study.

While many use propofol boluses for awake intubation, this technique must be used with great caution. Propofol and other sedatives decrease LES tone, predisposing to aspiration. In addition, the patient with airway compromise may depend on voluntary muscle tone for airway patency.154

Clearly, each situation is unique. An anesthetized airway in an awake patient can prevent gagging, retching, and coughing during intubation. In addition, the awake, cooperative patient maintains the LES tone and can anticipate vomiting and assist in maneuvers to prevent aspiration—turning their head to the side, opening their mouth for suctioning, etc.152 On the other hand, sedation can produce an uncooperative patient with depressed airway reflexes.

In the patient at high risk for aspiration, one must weigh each technique carefully in securing an airway while minimizing the risks of aspiration.

5.7.4 What Is the Appropriate Management for Aspiration?

When aspiration is suspected prompt measures should be taken to prevent further aspiration. The head of the bed should immediately be adjusted to a 30-degree head down position and the patient's head turned to the left side to facilitate drainage of secretions. The upper airway should be suctioned thoroughly. If the patient aspirates on induction, intubation should follow immediately with aggressive tracheal suctioning before ventilation, if possible. If intubation was not intended (as in procedural sedation) and the patient is spontaneously breathing, then supplemental oxygen by face mask should be applied after suctioning as one prepares for further assessment.5,155,156

As was mentioned earlier, damage to the lungs after the aspiration of gastric contents occurs within seconds, with subsequent neutralization of acid in 15 seconds. Consequently, bronchoscopy is not indicated except to remove large particulate matter. The decision to proceed with or cancel the surgery should depend on the severity of the aspiration, the patient's clinical status, and the urgency of the procedure. The patient should be notified that aspiration has occurred, when it is appropriate to do so and observed for signs of pneumonitis initially and pneumonia over the ensuing days.

Since gastric acid normally prevents the growth of bacteria, antibiotics are not indicated following aspiration alone. The incidence of progression to bacterial pneumonia following chemical lung injury is unknown. Symptoms of pneumonitis include wheezing, coughing, dyspnea, and cyanosis. Further complications may include pulmonary edema, hypotension, hypoxemia, and severe ARDS.23 Treatment of pneumonitis largely consists of supportive therapy, varying from simple oxygen supplementation to full ventilatory support.

5.7.5 Should Corticosteroids Be Administered Following the Aspiration of Gastric Contents?

The use of steroids following aspiration has been historically based on theoretical considerations, which remain unproven. These relate to anti-inflammatory properties, stabilizing effects on lysosomal membranes, ability to reduce platelet aggregation, and improvement of peripheral release of oxygen from erythrocytes.157 Studies conducted in the 1960s, 1970s, and 1980s consistently failed to prove a benefit of high-dose steroids after aspiration.158-160 Nevertheless, the practice continues23 despite a significantly higher death rate from secondary infections in the group receiving steroids.161

The use of high-dose steroids has not been proven effective and can adversely affect mortality in the critically ill population.5,161 Therefore, its use in episodes of aspiration is not recommended.

5.7.6 Should Antibiotics Be Administered to Prevent Pneumonia Following the Aspiration of Gastric Contents?

The majority of literature on the treatment of aspiration pneumonia is related to aspiration of colonized oropharyngeal secretions,23 not gastric contents. Treatment should focus on supportive care to maintain oxygenation followed by organism-specific antibiotic therapy should bacterial pneumonia develop. The incidence of post aspiration pneumonia is more common in debilitated patients with comorbid conditions, and patients who have been on ventilatory support, due to leakage around the tracheal tube cuff that occurs in these patients.

The proplylactic use of antibiotics after aspiration has not been demonstrated to prevent infectious pneumonia and is not recommended.162 Some exceptions may include patients with bowel obstruction23 and elderly or debilitated patients.162 The choice of antibiotics varies according to the syndrome and the clinical situation. For example, institutionalized elderly patients with aspiration pneumonia more commonly have anaerobic microorganisms cultured163 than other populations.

The recommendations for antibiotic selection change frequently and current guidelines for antibiotic therapy should be consulted. Such guidelines have been published by the following medical societies: American Thoracic Society,164 Infectious Diseases Society of America,165 Canadian Infectious Disease Society,166 and the Canadian Thoracic Society.166 Most commonly, it is recommended that antibiotic selection be guided by culture and sensitivity determinations.23

5.7.7 How Long Should the Patient Be Observed Following the Aspiration of Gastric Contents?

In a retrospective study of the perioperative course of 172,334 patients receiving general anesthesia, Warner et al6 reviewed 67 cases of aspiration. Forty-two of these patients, who were asymptomatic at 2 hours postaspiration or procedure, never manifested any symptoms, acute or delayed. Eighteen of these were day surgeries, and 12 were discharged home on the day of surgery. Twenty-four developed symptoms within 2 hours including cough or wheeze (17), decrease in arterial oxygen saturation of greater than 10% on room air (10), an increase in the A-a gradient greater than 300 (1), or radiographic changes (12). Of the 24 with symptoms, 18 required respiratory support or ICU admission, with 6 being ventilated for more than 24 hours because of the development of ARDS. Only one patient developed pneumonia and required antibiotics.

Patients who have been discharged home after suspected episodes of aspiration should be informed of the symptoms of pulmonary complications and instructed to report them promptly.

5.8 Summary

Listen

The prevention of aspiration is a significant focus of the airway practitioner. Certain factors markedly increase the risk of this event occurring. Some are inherent to the patients themselves, primarily premorbid conditions known to predispose to aspiration, some related to the patients' pathology and planned intervention, such as emergency surgery, bowel pathology, high ASA risk scores, pregnancy, difficult airway, and decreased level of consciousness. Airway management in the semiconscious patient may lead to coughing and gagging during attempts to secure the airway, accounting for over two-thirds of the perioperative aspirations.

Recognition of high-risk patients is important. Maneuvers to reduce gastric acid and volume, both pharmacologically and with drainage, may have their role but need to be targeted to specific situations. Bile and particulate materials are potentially as harmful to the lung as is the acid that tends to be the primary focus. Thus use of particulate antacids has been abandoned in the perioperative setting should they be aspirated.

Although the efficacy of the Sellick maneuver has come under recent criticism, it is still a standard of care in the protection of the airway at risk. A well-trained assistant is crucial. Under certain conditions when it hampers intubation or ventilation, the reduction or even release of cricoid pressure momentarily may be appropriate. The wisdom of the use of extraglottic devices in the high aspiration-risk patient, when other options are available, should be critically analyzed.

Finally, in the unlikely event that aspiration does occur, guidelines that are evidence based should be used in the assessment and management of these patients.

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5.2.1 When Was Gastric Aspiration First Described?

5.2.2 What Was Sellick's Approach to Minimize the Risk of Gastric Aspiration?

5.3.1 What Is the Incidence of Aspiration in Anesthesia Practice?

5.3.2 What Are the Risk Factors that Contribute to Aspiration? What About Nonanesthesia Settings?

5.3.3 What Happens during an Aspiration that Determines Its Severity?

5.4.1 What Is the Relevance of the Issues of Gastric Volume, pH, and Constituency of the Gastric Contents?

5.4.2 How Important Is a History of Heartburn? Acid Taste or Burping? a History of GERD? How Much Reflux Is Significant?

5.4.3 What Clinical Situations and Characteristics Predispose to Aspiration?

5.4.3.1 Emergency Surgery

5.4.3.2 ASA Physical Status

5.4.3.3 Airway and Intubation Difficulties

5.4.3.4 Obesity

5.4.3.5 Pregnancy

5.4.3.6 Age

5.4.3.7 Decreased Levels of Consciousness and Neurological Disease

5.4.3.8 Bowel Obstruction or Other Gastrointestinal Pathology

5.4.3.9 Full Stomach

5.4.4 Is There a Difference in Gastric Emptying in Emergency Patients or Those Who Have Received Opioids?

5.5.1 What Are the Current Fasting Guidelines? What Evidence Supports Their Use?

5.5.2 What Role Do Pharmacological Agents Play at Minimizing Aspiration Risk?

5.5.3 What Is the Role of Rapid-Sequence Induction?

5.5.4 Describe the Technique of RSI

5.5.4.1 Denitrogenation

5.5.4.2 Cricoid Pressure

5.5.4.3 Nasogastric Tubes and Gastric Evacuation

5.5.4.4 Sedatives/Hypnotics during RSI

5.5.4.5 the Choice of Muscle Relaxant during Rapid-Sequence Techniques

5.5.4.6 Positive Pressure Ventilation during RSI

5.6.1 Discuss the Applied Anatomy of Cricoid Pressure

5.6.2 What Is the Sellick Technique?

5.6.3 Does Cricoid Pressure Reliably Protect Against Regurgitation and Aspiration?

5.6.4 How Much Cricoid Pressure Is Needed to Prevent Gastric Regurgitation?

5.6.5 How Do You Measure the Performance of Cricoid Pressure?

5.6.6 Is Bimanual Cricoid Pressure Better Than a One-Handed Technique?

5.6.7 Does It Matter Which Hand Is Used to Apply Cricoid Pressure?

5.6.8 How Does Cricoid Pressure Affect Ventilation and Airway Interventions?

5.6.9 What Is the Impact of Cricoid Pressure on Cervical Spine Movement?

5.7.1 What Is the Aspiration Risk Associated with the Use of Extraglottic Devices?

5.7.2 Is It Safe to Use a Lightwand Intubation Technique (Eg, Trachlight™) in Patients at Risk of Aspiration?

5.7.3 Is Awake Intubation with an Anesthetized Airway Associated with a Lower Risk of Aspiration Than under Anesthesia?

5.7.4 What Is the Appropriate Management for Aspiration?

5.7.5 Should Corticosteroids Be Administered Following the Aspiration of Gastric Contents?

5.7.6 Should Antibiotics Be Administered to Prevent Pneumonia Following the Aspiration of Gastric Contents?

5.7.7 How Long Should the Patient Be Observed Following the Aspiration of Gastric Contents?

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