The ability to maintain a patent airway, provide adequate ventilation, and place an endotracheal tube remains a major concern for airway practitioners. There is no location that produces more anxiety in this regard than labor and delivery. Obstetrical anesthesia is a high-risk practice that is replete with medicolegal liability and laden with clinical challenges. On the obstetric service, the practitioner is required to provide safe anesthesia care to two patients, mother and baby, both of whom have unique and demanding anatomical and physiological requirements. The purpose of this chapter is to briefly review the status of maternal morbidity/mortality, highlight the principal reasons that airways of parturients might be difficult to manage, and propose an algorithm for the management of the obstetrical airway.
Underpinning all discussion is the critical importance of being prepared cognitively for the unexpected occurrence and being facile with appropriate emergency airway equipment. Early consultation for anesthesia intervention, and airway assessment of obstetric patients at high risk for operative intervention, particularly parturients who may be obese or have advanced maternal age, remain a key preventative pillar of care. Of equal importance is teamwork between the anesthesia practitioner, the labor and delivery nurses, and the obstetrician. Improved perioperative training of labor and delivery unit support staff (including anesthesia resources for airway management during and after general anesthesia) are important clinical care considerations. Practicing difficult airway scenarios is invaluable. Being unprepared will certainly guarantee failure.
49.2.1 Discuss the Anesthetic-Related Morbidity and Mortality of Parturients
Women continue to experience preventable pregnancy-related deaths, and anesthesia is the seventh leading cause of such mortality in the United States.1 These anesthesia-related deaths are particularly catastrophic, because many of these anesthetics are elective and are administered to young, otherwise well, mothers.
Hawkins and her colleagues characterized obstetrical anesthesia deaths in the United States by specific cause, relationship to type of anesthetic, and type of obstetrical procedure.2 Most women who died from anesthesia complications were undergoing cesarean section delivery (82%), whereas only about 5% of the deaths were associated with vaginal deliveries. Women who died of complications of general anesthesia (52% of all maternal deaths) primarily died as a result of airway management problems which included aspiration, intubation difficulties, and inadequate ventilation.
In 1985, a unique perspective on anesthesia morbidity and mortality was unveiled with the institution of the American Society of Anesthesiologists Committee on Professional Liability Closed Claims Project. The data from this project are an accumulation of personal damage insurance claims filed against anesthesiologists and subsequently settled.3 Of the nearly 6500 cases in the database, 12% have been associated with obstetrical anesthesia care and nearly three-fourths of these claims have been associated with cesarean section. Critical events involving the respiratory system were the most common precipitating events in the obstetrical files. Trauma from repeated attempts at intubation was recognized as an issue of particular hazard.
Obstetrical airway catastrophes occur most frequently during emergency cesarean sections. It is in these settings that regional anesthesia may not be possible because of either maternal condition or severe fetal distress. It is also in these settings that airway evaluation may be particularly hurried and harassed. Overall incidences of obstetrical airway problems are low (7.9%)4 but appear to be greater than in the non-obstetric patient (2.5%).5 Mask-ventilation can be difficult or impossible in approximately 0.02% of parturients, an incidence not dissimilar to other surgical patients.6
There is little prospective evidence and the literature is unclear as to the actual incidence of failed intubation under general anesthesia in obstetrical patients. While ranges have been given from 1 in 283 to 1 in 2130, a composite incidence of about 0.2%7 to 0.4%8 has been suggested. However, in a 2005 systematic review, Goldszmidt challenged the conventional wisdom and examined the evidence as to whether the obstetric airway is truly more difficult to intubate.9 In his review, difficult and failed intubation in the obstetric population was found to be rare, and there was no difference in the occurrence of difficult (1%-6%) or failed intubation (0%-0.7%) compared to general surgical populations.
While the incidence of a difficult airway in the obstetrical population remains unclear, there are concerns that the rates of failed intubation in the obstetric population will increase with declining numbers of women requiring general anesthetics, and the potential loss of skills in managing the airway of an obstetric patient.8,10-15
49.3.1 Why Do Parturients Have More Airway Complications Compared to the General Population?
The parturient is at significantly greater risk for airway complications and difficult intubations than her nonpregnant counterpart.16 A wide range of both anatomical and physiological changes occur during pregnancy and many of these may impact the airway directly, or indirectly (Table 49-1). Many of the changes are hormonally driven and the gravid uterus has a significant impact on the respiratory, cardiovascular, and gastrointestinal systems. Finally, there are a number of abnormal pregnancy-related processes that impact heavily on the parturient airway.
Table 49-1 Factors Affecting Management of the Parturient Airway ||Download (.pdf)
Table 49-1 Factors Affecting Management of the Parturient Airway
|Weight gain (12-20 kg)|
- Enlarging gravid uterus
- Increasing total body water and interstitial fluid
- Increasing blood volume
- Deposition of new fat
- Enlargement of the breasts
- Decrease in respirator reserve volume
- Decrease in functional residual capacity (20%-30%)
- Increased oxygen consumption
- More rapid desaturation
- Increased oral, nasal, pharyngeal, and tracheal mucosal edema
- Vascular engorgement of oral, pharyngeal, and nasal capillaries
- Edema of face and neck
- Advancement of Mallampati classification with pregnancy
- Advancement of Mallampati classification with bearing down during labor
- Inferior caval syndrome (supine hypotensive syndrome) requiring left uterine tilt
- Steadily increasing intragastric pressure as pregnancy progresses
- Decreased lower esophageal sphincter tone due to increasing progesterone
- Symptomatic gastroesophageal reflux
- Distortion of gastric anatomy
- Increased gastric acidity
49.3.2 How Do the Physiological Changes Associated with Pregnancy Impact the Airway of Parturients?
The difficulties in airway management for obstetrical patients may be related to a number of factors as discussed in the following sections.
During pregnancy, average weight gain can be 12 to 20 kg over the parturient prepregnant weight. This weight gain is related to increases in total body water, interstitial fluid (generalized body edema), blood volume, deposition of new fat and protein, uterine size and contents, and enlargement of the breasts.
Obesity (BMI >30) has become much more frequently encountered in the general population over the past decade. Mask ventilation is often difficult in obese patients because of reduced chest compliance and increased intra-abdominal pressure. The incidence of partially obliterated oropharyngeal structures in obese parturients is double that of non-obese parturients.4 In addition, weight gain may create a short neck, a large tongue, and large breasts, all of which contribute to difficult laryngoscopy. In the morbidly obese parturient (>140 kg or approximately 300 lb, BMI ≥40), the risks for diabetes, hypertension, preeclampsia, and primary cesarean delivery are all increased. There is also a higher incidence of difficult labor resulting in instrumental deliveries, postpartum hemorrhage, or other conditions that require anesthetic intervention.17
Morbidly obese parturients are at increased risks for anesthesia-related complications during cesarean delivery, and increased risks for failed intubation and gastric aspiration if general anesthesia is required.18 The cesarean section rate in these patients can exceed 50%, with one-third of attempted tracheal intubations being difficult and 6% being failures.19 In the ASA closed claims obstetrical files, damaging events related to the respiratory system were significantly more common among obese (32%) than non-obese (7%) parturients.20
184.108.40.206 Respiratory Changes
Respiratory changes during pregnancy are of special significance to the anesthesia practitioner. Over the course of a normal gestation, the parturient experiences a 30% to 60% increase in oxygen consumption, because of the metabolic demands of the growing fetus, uterus, and placenta. This, in combination with a reduction in functional residual capacity (FRC), which begins to decline as early as the fifth month and is reduced to 80% of nonpregnant values by term, invites exceedingly rapid desaturation with apnea. The tendency toward rapid desaturation is further aggravated by the supine position.
Displacement of abdominal contents toward the chest, as a result of the enlarged uterus, causes a reduction in FRC and premature airway closure, with widening of the alveolar-arterial oxygen gradient. As a result of these changes, oxygenation of the mother and fetus are easily compromised.21
Generalized edema may affect the oropharynx, nasopharynx, and trachea. These changes are aggravated by elevated estrogen levels that stimulate the development of mucosal edema and hypervascularity in the upper airways. Capillary engorgement of the nasal and oropharyngeal mucosa begins early in the first trimester and increases progressively throughout pregnancy. Accordingly, the parturient frequently appears to have symptoms of upper respiratory infection and laryngitis, with nasal congestion and voice changes due to swelling of the false vocal cords and arytenoids. Nasal obstruction from vascularity and edema may complicate bag-mask-ventilation (BMV).22
Numerous case reports suggest that edema of the pharyngeal and laryngeal structures, and vocal cords, may hinder visualization of the cords and passage of an endotracheal tube.23,24 Tongue edema may make retraction of the tongue into the mandibular space during laryngoscopy difficult. The increased engorgement and vascularity present special challenges in manipulating the nasopharynx (nasal trumpets, nasogastric tubes) or when considering repeated attempts at intubation. An endotracheal tube one size smaller than might be usual (ie, 6.0-7.0 mm ID) should be routinely used.
Excessive weight gain, even mild upper respiratory tract infections, preeclampsia, fluid overload, and bearing down, can all exacerbate airway edema potentially leading to a severely compromised airway. The classical Mallampati classification (Samsoon and Young modification) of mouth opening has been reported to advance by one or two classes during pregnancy.15 This may change even further as a consequence of bearing down, the score may not return to the pre-labor state for a further 12 hours postpartum.25,26 Acoustic reflectometry, which measures oropharyngeal volumes, and is likely a surrogate marker for ease of intubation, revealed decreased volumes both in women after delivery, and in women whose pregnancy was complicated by preeclampsia.22,26,27
220.127.116.11 Cardiovascular Changes
The supine position may result in compression of the aorta, the inferior vena cava, or both by the enlarged pregnant uterus. Compression of the aorta decreases uterine blood flow, impairing fetal oxygenation. Vena caval compression decreases venous return, cardiac output, and ultimately uterine blood flow. A combination of respiratory desaturation and compromised cardiac output is particularly lethal for the pregnant mother. It is therefore imperative that the parturient be positioned with a wedge under the right hip, creating left lateral displacement of the uterus, away from the great vessels. Unfortunately, such displacement may hinder adequate preoperative airway evaluation and the creation of an optimum position for intubation.
18.104.22.168 Gastrointestinal Changes
The risk of aspiration in the parturient impacts how the anesthesia practitioner approaches and manages the parturient's airway. Several factors increase the risk of aspiration in these patients. While intragastric pressure increases steadily during pregnancy, as the gravid uterus enlarges, a concomitant decrease in lower esophageal tone occurs as circulating levels of progesterone increase.
The enlarging uterus distorts esophageal and gastric anatomy. The cephalad pressure of the abdominal uterus decreases the obliquity with which the esophagus contacts the stomach, permitting reflux of gastric contents at lower than usual trans-sphincter pressures. Gastric emptying appears to be unaffected by pregnancy, though intestinal transit time and gastric acidity are increased. With the onset of labor, gastric emptying slows and may be further aggravated by the administration of opioids for labor pain management. Taken together, these gastrointestinal changes mandate that precautions be taken when a parturient undergoes general anesthesia.
22.214.171.124 Obstetrical Factors
There are a number of comorbid obstetrical factors that may put the parturient at risk for airway management difficulties and related complications. Gestational hypertension, eclampsia, and preeclampsia aggravate mucosal and interstitial edema.22 Concomitant proteinuria, with reduced intravascular plasma protein levels, leads to increased edema of the upper airway, an enlarged and less mobile tongue, and soft tissue deposition in the neck.
Preeclampsia is frequently accompanied by coagulopathy and edema, both of which may exaggerate bleeding with repeated attempts at direct laryngoscopy. Airway and laryngeal edema can develop exceedingly rapidly in preeclamptic patients and neck and face edema, and dysphonia from uvular edema, should alert the practitioner to the possibility of difficult intubation.28 In these patients, extreme caution should be exercised not only at intubation, but at the time of extubation as well.
Maternal knee-chest and left lateral positioning, as part of intrauterine fetal resuscitation for non-reassuring fetal heart tracings, may also limit ability to conduct adequate preoperative airway evaluation. The impact that this maternal positioning has on the validity, and the positive and negative predictive value of the preoperative airway assessment, is unknown.
Massive peripartum hemorrhage (eg, placenta previa, accreta, abruption) and acute fetal distress (eg, abruption, cord prolapse) are frequently encountered obstetrical emergencies occurring acutely and unannounced. The visual impact of profuse vaginal bleeding, or the slow ominous sound of the tocodynamometer with fetal distress, frequently pushes obstetricians and anesthesia practitioners to urgently proceed to general anesthesia, without taking the time to adequately assess the patient's airway. General anesthesia in the obstetric population is most frequently conducted for emergency clinical indications.29,30 Most airway catastrophes occur when the difficult airway is not recognized before the induction of anesthesia. Indeed, retrospective publications have reported poor ability to predict difficulty in the obstetrical population, and poor documentation of preoperative airway evaluation.8,13 Endler et al found that emergency surgery was implicated in up to 80% of maternal deaths with general anesthesia, and difficult or failed intubation was associated with 4 of 15 deaths.18
49.4.1 Why Is It Important to Assess the Airway of Each Parturient?
Every pregnant patient admitted to the labor and delivery service must have a thorough preanesthetic evaluation. With the always-present risk of acute-onset fetal distress, an essential and critical part of airway management is an accurate assessment of the patient's airway.
A detailed discussion of the airway examination and those predictors associated with management difficulties is found in Chapter 1. Most predictive studies have been conducted on general surgical populations, not parturients. Some 20 factors predicting difficult laryngoscopic intubation have been identified. The obstetrical patient presents unique assessment challenges, often the most important being a pressure of time.
49.4.2 How Do You Assess the Airway of a Parturient? What Are the Predictors or Risk Factors of a Difficult Airway for a Parturient?
The increasing use of regional anesthetic techniques for delivery has significantly decreased opportunity for research in patients undergoing general anesthesia. While parturients pose many unique airway challenges to anesthesia practitioners, assessment of the pillars of airway management (bag-mask-ventilation, the use of extraglottic devices, tracheal intubation, and establishment of a surgical airway) should not differ from the non-obstetrical population.
126.96.36.199 Difficult Bag-Mask-Ventilation
As discussed, difficult bag-mask-ventilation (BMV) can be difficult to impossible in approximately 0.02% of parturients. However, this incidence is comparable to the general surgical patient.6 While the mnemonic MOANS (see Section 1.6.1) is a helpful reminder of the five patient characteristics associated with difficult BMV,31 many of these characteristics do not apply to the obstetrical population. For example, young and healthy pregnant women are typically not older than 55 years of age, or edentulous, and they do not generally have facial hair. Obesity, however, is an important consideration and is becoming increasingly more prevalent amongst pregnant women. It is noteworthy that, 28% of pregnant patients and 75% of preeclamptic women reported snoring compared to 14% of nonpregnant women.22
188.8.131.52 Difficult Laryngoscopy and Tracheal Intubation
Section 1.6.2 discusses in detail the current evidence in assessing the predictors of difficult laryngoscopy and intubation (LEMON). Dupont and colleagues conducted one of the early airway studies in the obstetrical population32 and reported that the risk of difficult laryngoscopic intubation was eight times greater than in the general surgical population.
The literature suggests a variety of clinical signs that can help determine the degree of difficult laryngoscopic intubation (Table 49-2); however, none of these has a high positive predictive value as a single tool, particularly in the obstetrical patient. A number of studies suggest that, although the presence of risk factors was useful, they were not as reliable as the Mallampati examination. Benumof has frequently suggested that a patient's relative tongue/pharyngeal size (Mallampati), degree of atlanto-occipital joint extension, and adequacy of the mandibular space provide the clinician with three easy to perform and accurate predictors of difficulty in laryngoscopic intubation.33
Table 49-2 Features of the Airway Examination Useful in Predicting Difficult Laryngoscopy ||Download (.pdf)
Table 49-2 Features of the Airway Examination Useful in Predicting Difficult Laryngoscopy
|In the parturient|
- Mallampati Class III or IV
- Limited thyromental distance
- Short thick neck
- Limited mouth opening
- Prominent incisors
Rocke et al conducted one of the sentinel studies specifically looking at the obstetrical population and difficult airway predictors.4 They prospectively evaluated the airways of 1500 parturients presenting for elective and emergency intubations, and found that a highly predictive sign for a difficult airway was a neutral to extension sterno-mental distance variation of less than 5 cm. In addition, the authors built a scale of predictive factors showing clearly that the greater the number of abnormal findings, the higher the prediction accuracy for a difficult intubation (Figure 49-1). The associated risk factors included short neck (SN), protruding maxillary incisors (PMI), receding mandible (RM), and Mallampati Class III and IV. The relative risk of experiencing a difficult intubation in comparison to an uncomplicated Class I airway assessment was as follows: Class II, 3.23; Class III, 7.58; Class IV, 11.3; SN 5.01; RM, 9.71; and PMI, 8.0. Using the probability index, or combination of risk factors, Roche et al showed that a combination of either Class III or IV, plus PMI, SN, and RM, correlated with a probability of difficult laryngoscopy of greater than 90%. It was interesting that neither facial edema nor swollen tongue was associated with difficult laryngoscopic intubation. This may further support the concept that previously published increased rates of difficult and failed intubation in the parturient may in fact be related to anatomic abnormalities unrelated to pregnancy but rather emergency conditions, lack of preoperative airway assessment, or differences in intubation experience and expertise.9
The probability of experiencing a difficult laryngoscopic intubation for the varying combinations of risk factors and the observed incidence of these combinations. (From Rocke D, Murray W, Rout C, et al. Relative risk factors associated with difficult intubation in obstetric anesthesia. Anesthesiology. 1992,77:67-73, with permission.)
Overall, the mnemonic LEMON (see Section 1.6.2) examines almost all of the difficult laryngoscopic intubation characteristics (with the exception of the protruding maxillary incisors) and remains a useful guide for the obstetrical population.
In the obstetrical patient, obesity and large pendulous breasts often compound airway problems. It is important that the parturient be assessed in the recumbent position with left uterine displacement. Adjustments in the patient's position should be made before induction of anesthesia, to make intubating conditions easier, but there are limits to the extent that these adjustments can be employed, because of the positioning required to reduce aortocaval compression. In the morbidly obese parturient, elevations (ie, ramping) (Figure 49-2 and Chapter 17) of the thorax, shoulders, and head may be necessary to bring the anatomical axes of the oral, pharyngeal, and laryngeal structures into alignment. Positioning on a ramp may also mitigate the problem of the laryngoscope handle abutting on the patient's chest.
The Troop Elevation Pillow®: The pillow can help to raise the head and neck above the patient's chest and abdomen. The goal is to position the earlobes at the level of the Angle of Louis. (Courtesy from Mercury Medical.)
184.108.40.206 Difficulty in Use of Extraglottic Device
The use of an extraglottic device (EGD) is an important backup maneuver (Plan B) and serves as a bridging attempt to reestablish gas exchange in a "cannot intubate, cannot ventilate (CICV) setting, while one prepares to perform a cricothyrotomy in parturients. RODS (see Section 1.6.3) is a mnemonic that is intended to identify patients where the use of an EGD may be difficult.
220.127.116.11 Difficult Surgical Airway
While the necessity to perform a surgical airway, or cricothyrotomy, in an obstetrical population is exceedingly rare, all parturients requiring a general anesthetic ought to have an assessment of the feasibility of this maneuver. The mnemonic SHORT (see Section 1.6.4) can be used to quickly assess the patient for features that may indicate a difficult cricothyrotomy. Most obstetricians do not have experience in performing a surgical airway, and it is incumbent upon the anesthesia practitioner to maintain capacity in this regard. Nonetheless, it may be prudent to consult with an experienced surgical colleague for assistance when the need for surgical airway is likely.
49.4.3 When a Difficult Laryngoscopy Is Anticipated in a Parturient, Is It Useful to Perform an Awake Direct Laryngoscopy (an Awake Look)?
Awake direct laryngoscopy with a topically anesthetized airway (ie, awake look) has been suggested as useful assessment tool of the potentially difficult airway prior to induction of anesthesia. However, one must recognize that the airway as it appears with the patient awake and unparalyzed might look quite different with the patient under general anesthesia and with muscle paralysis.34
49.5.1 What Are Necessary Preparations for General Anesthesia for a Parturient?
There are several preparations that must be made on the labor and delivery suite to ensure safe and expeditious care of the parturient should general anesthesia be required.
The operating room bed should have a ramp on it at all times (Figure 49-2 and Chapter 18). This will prove to be an invaluable aid in optimizing head position and will help align the oral, pharyngeal, and laryngeal axes in the obese parturient. Furthermore, it will not be problematic in the patient with easy tracheal intubation.
It is important to have all difficult airway equipment in the operating room. It is also important to recognize the importance of having well-trained assistants to help with all aspects of airway management, including rescue devices, as well as application of cricoid pressure. Because time is often of the essence, and resources often limited, the practitioner must carefully choose devices with which they are familiar and comfortable, and techniques that can be practiced regularly.
Table 49-3 details some of the suggested equipment necessary to manage the difficult airway on the labor floor. A short laryngoscope handle (stubby) can be particularly helpful.
Table 49-3 Equipment Required for Management of Difficult OB Airway ||Download (.pdf)
Table 49-3 Equipment Required for Management of Difficult OB Airway
|Bed ramp||Troop pillow (Figure 49-2)|
|Oral airway||Three sizes|
- Eschmann Tracheal Introducer (Portex Limited, Hythe, UK)
- Frova intubation introducer (Cook Inc., Bloomington, IN, USA)
|Endotracheal tubes||At least three different sized (6.0, 6.5, 7.0)|
Stubby short handle
- Classic #3, #4
- ProSeal #3, #4
- Fastrach #3
ILA (intubating laryngeal airway)
|Percutaneous cricothyrotomy kit|
All obstetrical patients requiring general anesthesia must receive aspiration prophylaxis (nonparticulate antacid and H2 blocker). Induction must be in rapid-sequence fashion including the application of cricoid pressure. Recent work has shown that, even when correctly applied, cricoid pressure may not always be completely effective.35 Nevertheless, it has the potential to convert a flood into a trickle.
Because the pregnant patient is at increased risk for hypoxemia, even during short periods of apnea, it is especially important that adequate denitrogenation with 100% oxygen prior to the induction of general anesthesia is performed. Various techniques for denitrogenation have been advocated. Norris and Dewan observed that 3 minutes of denitrogenation, and the four-breath denitrogenation technique, resulted in similar measurements of Pao2 in pregnant women undergoing rapid-sequence induction of general anesthesia for cesarean section.21 If the tidal volume is large, and the respiratory rate is high, denitrogenation may need to be only 1 minute in duration. However, this 1 minute can be one of the most important minutes of the induction and should not be further abbreviated.
49.5.2 Describe an Appropriate Algorithm for a Difficult/Failed Intubation in a Parturient
The difficult airway algorithm in the parturient is significantly different from that used in the operating room for non-obstetrical surgical patients. In general, the differences focus on the presence or absence of fetal distress.
Frequently, general anesthetics on the labor and delivery service are required in patients with whom the anesthesia practitioner has little or no foreknowledge. In addition, the environment is often volatile, with considerable pressure to proceed with an emergency induction, because fetal viability is in question and fetal rescue is required. In such an event, it is imperative that the practitioner has a simple, clear algorithm to follow when a difficult airway is encountered. Equally important is that the practitioner regularly practices this algorithm with the labor and delivery personnel, and that they are familiar with the airway devices that might be employed in an emergency.
18.104.22.168 Anticipated Difficult Airway
When the anesthesia practitioner anticipates a difficult airway, a regional anesthetic technique may be preferable (Table 49-4). However, there are numerous conditions that may preclude the use of regional anesthesia. When regional anesthesia is not possible, one of the first things that must occur is a thorough discussion with the obstetrician, the patient, the patient's family, and nurses, pointing out any airway management concerns that the anesthesia practitioner has. In some circumstances, the anesthesia practitioner ought to make it clear that the patient's airway management cannot be hurried, implying that a decision to go to surgery may need to be made earlier rather than later. The hope is that one is not pushed into a general anesthetic when more deliberate planning may have permitted a regional technique.
Table 49-4 Important Points for Managing the Anticipated Difficult Obstetrical Airway ||Download (.pdf)
Table 49-4 Important Points for Managing the Anticipated Difficult Obstetrical Airway
|Identify parturients at high risk for operative intervention|
- Advanced maternal age
- Non-reassuring fetal or maternal conditions
|Detailed discussions with the obstetrician concerning delivery plan|
- Crash induction is not an option
- Speak to patient and family early in labor
- Persist with regional techniques
- Awake intubation if necessary—using a flexible bronchoscope
- Wishful thinking is a poor anesthetic plan—know that your regional technique is working
In those instances when regional anesthesia is contraindicated, an anticipated difficult airway is recognized, and time permits, an awake intubation technique should be employed. Flexible bronchoscopy (FB) has become the method most frequently used. The specifics of this technique are found in Chapter 9. However, there are several points that should be reiterated for the obstetrical patient. Because the parturient airway is often edematous, and engorged, topicalization of the upper airway can frequently be difficult and requires considerable patience. A drying agent is necessary and aspiration prophylaxis must be initiated before topical anesthesia begins. One should not hesitate to sedate the mother as needed.
Blind nasal intubation is an option that must be approached with caution. Any attempt at nasal instrumentation incurs the risk of nasal and pharyngeal bleeding that can compromise subsequent efforts at direct laryngoscopy or bronchoscopic intubation.
Retrograde intubation techniques have been shown to be valuable in the management of the difficult airway in the past, but have little, if any, value today in the care of the obstetrical patient.
There are a host of specialized fiberoptic or video laryngoscope blades and handles (eg, Bullard, GlideScope®, UpsherScope™, Storz Videoscope), each with individualized bulbs, light sources, or fiberoptic bundles ending at various distances into the oral pharynx (see Chapter 10). Considerable effort is needed to maintain these and considerable practice is necessary to become skilled in their use. Certainly, for the anticipated difficult airway in which time and technical assistance will be available, these devices may be useful. However, in general, time and assistance are perpetually in short supply on labor and delivery services.
22.214.171.124 Unanticipated Difficult Airway
Table 49-5 lists several important points to remember in managing an unanticipated difficult obstetrical airway. Figures 49-3 and 49-4 are algorithms one might choose to use in the event of an unanticipated failed tracheal intubation in the obstetrical patient. Figure 49-3 outlines the critical breakpoints in the management of an obstetrical patient requiring general anesthesia: anticipated versus not anticipated; adequate ventilation versus inadequate ventilation; fetal distress versus no fetal distress.
Table 49-5 Important Points for Managing the Unanticipated Difficult Obstetrical Airway ||Download (.pdf)
Table 49-5 Important Points for Managing the Unanticipated Difficult Obstetrical Airway
|Thorough and careful airway evaluations|
- Know your predictors—which ones work for you
|Strategy for intubating the difficult airway|
- Pick your algorithm ahead of time
|Make basic preparations for the difficult airway|
- Pick your equipment ahead of time (LMA, LMA-Proseal™, LMA-Fastrach™, Eschmann, Combitube™, jet ventilator, cricothyrotomy kit)
- Keep it simple—get real with your gadgets
- Practice, practice, practice
Basic decision points for the Difficult Airway Algorithm in the obstetrical patient.
Difficult Airway Algorithm in the obstetrical patient.
If ventilation is possible, the decision to continue hinges on the presence or absence of fetal distress. If there is no fetal distress, the patient should be awakened and an alternative anesthetic technique chosen. If, on the other hand, fetal distress is present, one may elect to continue with the case using mask ventilation or an EGD. The patient continues to be at risk of aspiration and cricoid pressure should be continued.
If ventilation is impossible, the patient should be allowed to wake up regardless of the presence of fetal distress. In the interim, rescue techniques may be necessary. Placing the LMA-Classic™, LMA-Fastrach™, or LMA-Proseal™ could be lifesaving in this instance. If, during the awakening process, ventilation is reestablished, one may then elect to continue with the case, if fetal distress is present. A more critical situation is one where, in addition to fetal distress, obstetrical hemorrhage or some other life-threatening condition for the mother exists. Most situations of antepartum hemorrhage do not improve until delivery of the fetus and placenta. The LMA-Fastrach™ may be an excellent choice in this setting.
Several alternative methods to mask ventilation have been described which, of necessity, can be instituted quickly; insertion of the Esophageal Tracheal Combitube™; or insertion of an LMA (Classic, ProSeal, and Fastrach ILMA). If these fail, one may institute trans-tracheal jet ventilation, or perform an emergency cricothyrotomy, or tracheotomy.
The Combitube™ is a plastic twin-lumen tube that can be placed blindly and, when properly positioned, serves to seal the esophagus and ventilate the trachea (see Section 12.6). The Combitube™ has been employed in diverse clinical circumstances to provide adequate ventilation and oxygenation. There is only one report of its use in the parturient.36 A major drawback of the Combitube™ is that it is a disposable device that one would not use electively and, therefore, not something one can easily practice with in nonemergency situations.
The laryngeal mask airway (LMA) is a well-established device in the ASA difficult airway algorithm and must be part of every difficult airway cart on the labor and delivery floor. The LMA has rapidly become a mainstay in difficult airway management because it is used on a daily basis and practitioners are comfortable with its use. The LMA has been used effectively and safely in selected healthy non-obese parturients, although this is not a practice that the authors would support, other than as a rescue maneuver.37 When the LMA is placed in the failed intubation/failed ventilation scenario, cricoid pressure should be continued.
The LMA-Proseal™ is a redesigned LMA that may offer a degree of protection against aspiration to the parturient, in comparison with the LMA-Classic™. The LMA-Proseal™, designed to facilitate controlled ventilation and to mitigate the potential for reflux, has been used successfully in failed intubation emergency cesarean section.38
Finally, the LMA-Fastrach™ may have a significant advantage over the LMA-Classic™, or the LMA-Proseal™, in the obstetrical patient. Following placement of the LMA-Fastrach™, an endotracheal tube can be placed through the LMA to secure the airway.
While transtracheal jet ventilation (TTJV) is said to be simple, quick, and relatively safe, it is technically difficult to perform in obstetrical patients. As reports of catastrophes have surfaced with TTJV during emergency situations, this technique has slowly lost favor and is seldom used in favor of using the LMA, or a surgical cricothyrotomy.
A surgical airway is indicated when one is confronted with a failed airway. Percutaneous surgical cricothyrotomy is a viable alternative to open surgical cricothyrotomy. Several kits have become commercially available. These kits appear to be simple, rapid, and safe to use. There is increasing enthusiasm that anesthesia practitioners learn this technique, instead of TTJV.
Difficult or failed intubation is a major contributor to maternal morbidity and mortality during obstetrical emergencies. Careful preanesthetic evaluation focusing on the parturient's airway should identify patients at risk for difficult airway management. Early communication with the obstetricians, regular review and practice of a formal Difficult Airway Algorithm, and facility with current difficult airway devices should mitigate some of the risk of injuries to parturients when a failed intubation does occur.