Chapter 40. Airway Management in the Operating Room of a Morbidly Obese Patient in a "Cannot Intubate, Cannot Ventilate" Situation

A 68-year-old man is scheduled for an elective anterior cervical decompression and fusion due to a progressive cervical radiculopathy with numbness and pain in the C6 distribution bilaterally. He has stable coronary artery disease with Class II angina and well-controlled type 2 diabetes mellitus. He is a nonsmoker and has no history of sleep apnea. He has no allergies and he is taking metoprolol, amlodipine, glyburide, and is on a nitroglycerine patch.

His chest is clear and heart sounds are normal. His airway examination reveals that he is edentulous with a full beard. He has a Mallampati Class II pharyngeal view, a 6.0 cm thyromental distance, and 4.0 cm of mouth opening. There is a slight reduction of neck extension (approximately 30 degrees). He is 170 cm tall (5 ft 7 in), and weighs 110 kg (242 lb) with a BMI 38 kg·m−2. His vital signs are: blood pressure (BP) 140/95 mm Hg, heart rate (HR) 64 beats per minute (bpm), respiratory rate (RR) 20 breaths per minute, SpO2 95% on room air.

Laboratory investigations reveal normal CBC, electrolytes, and creatinine. The random blood glucose is 7.1 mmol·L−1. He has a normal ECG. An MRI of the cervical spine shows disc protrusion at the C4-5 and C5-6 levels causing nerve root compression at the C6 level bilaterally and CSF effacement in front of C4-5 and C5-6 levels without signal changes in the spinal cord.

A diagnosis of cervical radiculopathy has been made.

40.2.1 What Are the Anesthetic Considerations for a Morbidly Obese Patient with a BMI of 38?

Morbid obesity is associated with a number of anatomic, physiologic, and biochemical changes (see also Chapter 18).1 The cardiovascular system of obese patients is characterized by increased cardiac output, increased circulatory blood volume, and an increased incidence of systemic hypertension and coronary artery disease. In the respiratory system, they have increased oxygen consumption, increased carbon dioxide production, reduced functional residual capacity, increased premature airway closure and shunt, decreased chest wall compliance, and increased work of breathing. There is an increased incidence of pulmonary hypertension and obstructive sleep apnea. There is also a higher incidence of hiatus hernia, gastroesophageal reflux, glucose intolerance, and diabetes mellitus. Airway considerations are detailed later.

40.2.2 Is This Patient at an Increased Risk of Having a Perioperative Cardiac Event?

Yes. This patient has several risk factors and is at a higher risk of having a perioperative cardiac event. There are several well-established perioperative cardiac risk assessment tools. He has diabetes and stable, functional Class II angina which according to the 2007 ACC/AHA guidelines2,3 are two clinical risk factors. Utilizing the Lee cardiac risk score,4 he has two (CAD and diabetes) of six risk factors and is predicted to have a perioperative cardiac event rate of approximately 5%. Utilization of perioperative beta-blockade may be useful in reducing his risk of cardiac events.

40.2.3 Some Patients with Cervical Spine Pathology Scheduled for Anterior Decompression and Fusion Undergo Awake Intubations. Does Our Patient Need One?

It is the opinion of the author that three categories of patients may require awake endotracheal intubation:

• The first group has signs and symptoms of cervical myelopathy. Clinically, this may manifest itself as bilateral upper extremity numbness, pain or weakness, or long track signs such as bilateral leg symptoms. These symptoms may worsen with certain neck movements. Radiologically, cerebral spinal fluid effacement, deformation of spinal cord contour, and particularly signal changes within the spinal cord are suggestive of myelopathy. Although there are no studies which show that patients with spinal cord pathology or injury have improved outcome when intubated awake versus asleep.5-8 The author believes that patients with clinically evident myelopathy should have an awake endotracheal intubation to avoid the possibility of further spinal cord compromise with neck movement encountered during asleep intubation.
• Second, patients with cervical spine ligamentous or bony instability constitute another potential indication for awake intubation. Examples include C1-2 subluxation from rheumatoid arthritis or traumatic cervical spine instability.
• Third, patients with proven or suspected difficult airways should be considered for awake intubation.

40.2.4 Should This Patient Be Admitted to the ICU Postoperatively to Monitor for Airway Swelling and Compromise?

It is possible that patients undergoing anterior cervical decompression and fusion are at a slightly increased risk of postoperative airway obstruction. However, it is reasonably safe to observe these patients in the PACU for 4 to 6 hours postoperatively, and if they have an uneventful course, discharge them to the floor. We have used the above protocol for management of postoperative anterior cervical spine fusion patients for more than 6 years in our institution and have not encountered any significant airway problems on the first day postoperatively. Patients who undergo prolonged surgery, multiple segmental fusion, corpectomy, difficult surgical exposure with excessive traction, massive fluid shifts, or those who have received large amounts of intravenous (IV) fluids should be admitted directly to the ICU.

Postoperatively, it is crucial that the patient be followed closely for the onset of stridor, increasing difficulty in swallowing or breathing, or signs of increasing external neck swelling. Airway obstruction can occur rapidly in the face of a neck hematoma, edema, lymphatic obstruction, or nerve palsies. Patients exhibiting any of the above signs or symptoms in the immediate postoperative period should immediately have an examination of the airway awake under topical anesthesia using a flexible nasopharyngoscope. Should the airway look normal and intubation is deemed to be unnecessary, close and continuous observation is indicated. If the airway is narrowed or partially obstructed, it should be secured using an awake endotracheal intubation technique. Life-threatening airway obstruction can rapidly ensue either spontaneously, with airway topicalization, or upon airway instrumentation.9-11 It is imperative to have immediate availability of equipment and personnel skilled in insertion of an infraglottic airway in anticipation of complete airway obstruction.

40.3.1 How Often Does Difficult Intubation Occur in Clinical Practice? How Is Difficult Intubation Defined?

The incidence of difficult intubation depends on its definition. In 1993, the ASA task force12 defined difficult intubation as occurring when "proper insertion of the tracheal tube with conventional laryngoscopy requires more than three attempts or more than 10 minutes." In 1998, the Canadian Airway Focus Group13 used the following definition: "when an experienced laryngoscopist using direct laryngoscopy, requires: (1) more than two attempts with the same blade or; (2) a change in the blade or an adjunct to a direct laryngoscope or; (3) use of an alternative device or technique following failed intubation with direct laryngoscopy." The incidence of difficult intubation reported in the literature ranges from 1.15% to 3.8%.13

40.3.2 Is the Patient Predicted to Have a Difficult Airway? How Accurate Are Our Predictions for Difficult Intubation?

The ASA Task Force on Management of the Difficult Airway outlined 11 criteria for preoperative airway assessment.14 No single airway test has perfect sensitivity or specificity in predicting difficult intubation. In general, many single airway predictors share a common set of characteristics: low sensitivity, high specificity, and low positive predictive value. Combinations of several airway predictors tend to improve the positive predictive value for difficult intubation. (See Chapter 1.)

Our patient had a Mallampati II score, a thyromental distance of 6.0 cm, mouth opening of 4.0 cm, slightly reduced cervical extension, and a full set of dentures. In combination, these characteristics place this patient at low risk of difficult laryngoscopic intubation.

40.3.3 Is There a Concern About Difficult Bag-Mask-Ventilation in Our Patient? How Is Difficult Mask Ventilation Defined?

The ASA Task Force on Management of the Difficult Airway defined difficult bag-mask-ventilation as: "it is not possible for the anesthesia practitioner to provide adequate face mask ventilation due to one or more of the following problems: inadequate mask seal, excessive gas leak, or excessive resistance to the ingress or egress of gas."14 The incidence of difficult bag-mask-ventilation is in the range of 5%15 while failed bag-mask-ventilation is in the range of 0.01% to 0.08%.13

Langeron identified five risk factors for difficult mask ventilation: beard, obese (BMI >26), age greater than 55, lack of teeth, and history of snoring (MOANS, see Section 1.6.1).15 Our patient has four of the five risk factors and is at a moderately increased risk of difficult mask ventilation. More recently, Kheterpal et al identified independent predictors for difficult or impossible mask ventilation: obese (BMI >30), beard, Mallampati III or IV, age = 57, limited jaw protrusion, snoring, neck radiation, male gender, and obstructive sleep apnea.16,17

40.3.4 How Often Does the "Cannot Intubate, Cannot Ventilate" Situation Arise in Clinical Practice?

"Cannot intubate, cannot ventilate" (CICV) situations are life threatening. In 1991, the incidence of CICV was estimated to be 0.01 to 2 per 10,000 patient cases.18 The LMA has since been shown to be effective in providing rescue ventilation in the majority of CICV situations.19 The current incidence of CICV requiring emergency infraglottic airway insertion may be lower than 2:10,000 patients. Anesthesia practitioners need to be fully prepared to insert an infraglottic airway in this rare but deadly situation.

40.4.1 How Do You Plan to Intubate the Trachea of This Patient?

The patient is undergoing an anterior cervical fusion and will require general anesthesia with endotracheal intubation. As he does not have cervical myelopathy, instability, or prediction of a difficult intubation, the plan is to proceed with endotracheal intubation after IV induction of general anesthesia.

40.4.2 Are You Concerned About Difficulties in Mask Ventilation?

Yes. The patient is at an increased risk for difficult mask ventilation but is not predicted to have a difficult laryngoscopic intubation or difficulty in using an extraglottic device. Therefore, a variety of airway devices are prepared including face masks, nasopharyngeal airways, oropharyngeal airways, Eschmann Tracheal Introducer (bougie), Laryngeal Mask Airways, and the Combitube™. Operating room personnel are alerted to the possible need to perform two-person bag-mask-ventilation.

40.4.3 What Are Your Plans If after the Induction of General Anesthesia, Intubation with a Direct Laryngoscope Is Unsuccessful But Ventilation Is Easy Using Bag-Mask Technique?

This unsuccessful intubation, but adequate ventilation clinical setting places us in the second tier of The Failed Airway Algorithm (see Chapter 2) and in the middle of the ASA Difficult Airway Algorithm nonemergency pathway.14 If all six factors defining an optimal laryngoscopic attempt (see Section 1.6.2) have been met, it makes no sense to persist with further attempts with direct laryngoscopy. Instead, since one has time, alternative approaches such as use of the flexible bronchoscope, intubating laryngeal mask airway, lighted stylet, or the GlideScope® may be attempted.20,21 It is important to impose a time or number of attempts limit when using these alternative techniques such that a CICV situation following repeated airway instrumentation does not occur. In the event that intubation is unsuccessful after multiple attempts with alternative techniques in a nonemergency scenario, the patient should be awakened and an awake intubation performed.

40.4.4 Should This Evolve into a CICV Situation after the Induction of General Anesthesia, What Should One Do? (Table 40-1)

CICV is an absolute medical emergency. Hypoxic brain damage and death can ensue unless successful corrective measures are undertaken immediately. CICV may occur immediately after induction of anesthesia or during the course of repeated airway instrumentation. The Failed Airway Algorithm directs one to immediately prepare to perform a cricothyrotomy, although while preparations are underway one may attempt to place an extraglottic device (EGD, [LMA or Combitube™]). This differs from the ASA Difficult Airway Algorithm,14 in that these interventions occur concurrently rather than sequentially. If ventilation and oxygenation become adequate with an EGD, time becomes available to attempt alternative techniques.

40.4.5 A CICV Situation Wherein the Patient Becomes Progressively Hypoxemic Necessitates an Immediate Surgical Airway. What Is Your Preferred Technique and Instrument? (Table 40-1)

The most common techniques employed to secure an infraglottic airway include percutaneous IV catheter cricothyrotomy; percutaneous dilational cricothyrotomy; open surgical cricothyrotomy; and surgical tracheotomy (see Chapter 13). In a Canada-wide anesthesiologist survey,22 respondents preferred using cricothyrotomy by intravenous catheter (51%), followed by percutaneous dilational cricothyrotomy (28%) and tracheotomy by surgeon (7%).

40.4.6 What Are the Advantages and Disadvantages of These Infraglottic Airway Techniques?

Although cricothyrotomy by IV catheter is the simplest to perform, it is difficult to fixate the catheter, is difficult to maintain patency, offers no airway protection, provides variable amounts of ventilation, lacks a conduit for suction, is associated with significant risks of barotraumas, and requires a special attachment for jet ventilation.22 Scrase et al23 concluded in a review article that jet ventilation does not provide adequate ventilation via an IV catheter and is potentially dangerous. Anesthesia practitioners are generally uncomfortable performing an open cricothyrotomy. The percutaneous dilational cricothyrotomy technique incorporates many advantages of the open cricothyrotomy. It is more stable, offers airway protection, provides a conduit for suctioning, and can be readily connected to a ventilation bag with a 15-mm connector. Furthermore, the percutaneous Seldinger dilational technique is familiar to most airway practitioners who perform central venous cannulation. Most anesthesiologists in the above survey were unfamiliar with the methodology and instruments involved in open tracheotomy or cricothyrotomy.22

40.4.7 Is There Evidence in the Literature to Indicate Which Cricothyrotomy Technique Is Superior to Others in Terms of Speed of Insertion and Success Rates?

Review of the literature reveals few randomized controlled trials using infraglottic airway techniques and none in actual patients in CICV situations.24,25 Eisenburger et al26 compared the performance of percutaneous wire-guided and surgical cricothyrotomy by intensive care trainees on cadavers. The cricothyrotomy times were 100 seconds and 102 seconds, respectively. Chan et al27 did a similar comparative study for emergency medicine attending physicians and residents. He found similar times (75 vs 73 seconds) for the percutaneous and surgical cricothyrotomy groups. Schaumann et al compared the performance of percutaneous and surgical cricothyrotomy on cadavers by emergency physicians.28 The cricothyrotomy times were significantly shorter in the percutaneous compared to the surgical group (108.6 vs 136.6 seconds). In contrast, Dimitriadis et al29 and Sulaiman et al30 showed that surgical cricothyrotomy insertion times were significantly shorter than percutaneous wire-guided technique in a mannequin model.

40.4.8 Many Airway Practitioners Have Never Performed a Cricothyrotomy or Encountered a CICV Situation. How Can One Acquire Proficiency in the Performance of Infraglottic Airway Insertion?

To optimize the success rate of surgical cricothyrotomy, it is necessary to commit to memory all the sequential steps and to acquire experience in a simulated setting. Bainton reported that the time taken to perform a cricothyrotomy on dogs improved significantly after practicing on cricothyrotomy simulator models.31 Wong et al32 showed that procedure times and success rates improved significantly in 102 subjects, each performing 10 consecutive cricothyrotomies on mannequins. From the first to tenth attempt, procedure times improved from 41.2 seconds to 24.4 seconds (41% change) and success rate went from 62% to 99% (37% change). Knowing the cricothyrotomy equipment, familiarity with a cricothyrotomy procedure algorithm, and practical experience with using such devices on mannequins provide the practitioner the best chance of success when called upon to perform a cricothyrotomy in an emergency, such as a CICV airway.

40.4.9 How Do You Plan to Denitrogenate This Patient Prior to Anesthesia Induction?

There are many reasons to ensure adequate oxygenation prior to induction. First, the patient is morbidly obese which is associated with reduced functional residual capacity, increased airway closure and shunt, decreased chest wall compliance, and increased work of breathing. He will desaturate much faster than a normal individual with hypoventilation. Second, he is potentially difficult to bag-mask-ventilate. Provision of supranormal denitrogenation will provide the patient and anesthesia practitioner a wider margin of safety on induction. Third, he has significant coronary artery disease. With his increased cardiac oxygen requirement due to obesity and reduced coronary reserve, he may not be able to tolerate arterial hypoxemia. Therefore, the goal should be to provide denitrogenation for at least 3 minutes and end-tidal O2 ≥90%, similar to that in rapid-sequence induction.

40.5.1 How Was the Induction and Airway Management Approached?

Anesthesia equipment and drugs were fully prepared prior to induction. The patient was denitrogenated for 5 minutes, pretreated with fentanyl, induced with propofol, and paralyzed with rocuronium. After 2 minutes, direct laryngoscopy with a MAC #3 blade was attempted. Only the epiglottis was visible. A MAC #4 blade was tried with the application of anterior laryngeal pressure with no improvement of laryngeal view. A blind insertion of a styletted endotracheal tube behind the epiglottis was performed, but no CO2 waveform was detected and the endotracheal tube was removed. Bag-mask-ventilation was performed but due to a large mask leak the SpO2 decreased to 88%.

We now have a failed intubation coupled with borderline bag-mask-ventilation. A 9.0 mm oral-pharyngeal airway and two nasal airways were inserted. The anesthesia practitioner then performed a two-hand mask hold while ventilation was provided by the operating room nurse. Despite these measures, the SpO2 continued to decline to 80%.

40.5.2 Confronted with a "Cannot Intubate, Cannot Ventilate" Situation, What Ought to Happen Next?

Cricothyrotomy! In the meantime, as the cricothyrotomy equipment is being set up, one may attempt an intubating LMA or other EGD. This should not be a sequential step, as indicated in the ASA Difficult Airway Algorithm; it is concurrent with preparation to perform a surgical airway as in The Failed Airway Algorithm (Chapter 2). If the EGD rescue is successful and adequate ventilation is restored, then intubation attempts with alternative intubation equipment, such as a flexible bronchoscope and GlideScope® are appropriate. However, in the CICV situation, attempts to intubate with alternative techniques, such as the flexible bronchoscope and GlideScope® are not appropriate and waste valuable time.

In this case scenario, the patient was hypoxemic and deteriorating in a CICV situation. A decision was made to insert an infraglottic airway immediately. Concurrently, an LMA was inserted, but ventilation via the LMA was not successful. The anesthesia practitioner decided to use a percutaneous dilational cricothyrotomy technique.

40.5.3 Describe the Actual Steps Taken to Insert the Percutaneous Dilational Cricothyrotomy

The instrument used to perform cricothyrotomy was a preassembled Melker emergency percutaneous dilational set (Cook Critical Care) which consisted of a needle, syringe, guide wire, scalpel, dilator, and airway, which in the newer sets is cuffed. (See Chapter 31 for details.) The cricothyroid membrane was located and punctured with an 18-gauge needle directed caudally. Correct intraluminal location of the needle in the airway was confirmed by the aspiration of air (Figure 40-1). The 0.038-in guide wire was inserted via the needle into the airway (Figure 40-2) and the needle was removed over the wire. The puncture site was enlarged by a stab with a #15 scalpel blade, and a cuffed tracheotomy tube or airway catheter (5.0 mm ID) with the dilator (18 FR) (Figure 40-3) inserted into the trachea over the wire (Figure 40-4). The dilator and the wire were removed, ventilation was performed, and correct placement was confirmed using capnography and auscultation. A CO2 waveform was obtained and the SpO2 improved to greater than 90% 2 minutes after establishment of ventilation via the cricothyrotomy.

40.5.4 Is It Feasible to Perform an Open Surgical Cricothyrotomy Instead of the Percutaneous Dilational Approach?

Yes, it is a feasible option. Most anesthesia practitioners are not comfortable with a surgical cricothyrotomy; but many surgeons and emergency room physicians are.22 The technique consists of locating the cricothyroid membrane; making a midline longitudinal incision through skin; followed by a transverse incision through the cricothyroid membrane using a scalpel; insertion of a tracheotomy hook placed beneath the inferior border of the thyroid cartilage; applying traction in an anterior/cephalad direction to expose the airway lumen; placement of an endotracheal or cricothyrotomy tube; and confirmation of positioning using capnography and auscultation (see Section 13.2.1). Open cricothyrotomy kits are commercially available. Alternatively, the necessary equipment can be assembled by the individual institution and potential practitioners made aware of the contents.

40.6.1 At Present, Oxygenation and Ventilation Are Satisfactory. What Is Your Next Step?

Although there is some controversy, most consider a cricothyrotomy to be a temporary life-saving airway which should not be maintained for prolong periods (see Chapters 13 and 31). Therefore, a surgeon was requested to perform a tracheotomy. A size 8.0 mm ID cuffed tracheotomy tube was inserted and the temporary cricothyrotomy was removed.

40.6.2 Now that the Airway Is Secured, the Neurosurgeon Is Anxious to Proceed with the Anterior Cervical Fusion. Should We Go Ahead?

No. The surgery is elective. The patient almost died due to a failed intubation and was subjected to repeated airway instrumentation before a surgical airway was secured. There are three reasons for not performing the surgery at this time. First, anterior cervical fusion involves traction and manipulation in the neck. Should the tracheotomy tube be dislodged, it may be very difficult to reinsert through the track of a newly created tracheotomy. Second, cervical surgery in addition to the intubation attempts will increase the risk of postoperative airway edema. Third, having a tracheotomy tube in the immediate vicinity of a fresh surgical incision increases the potential for surgical site infection.

40.6.3 As a Decision Has Been Made Not to Proceed with Cervical Surgery, What Do We Do Next?

The patient was brought to the ICU. He was ventilated and allowed to awaken. Once awake and adequate spontaneous ventilation was reestablished, he was removed from the ventilator and placed on a tracheotomy mask. The patient was discharged to the surgical floor after overnight observation.

40.6.4 When Can We Bring Him Back for His Cervical Fusion?

A reasonable course of action is to remove his tracheotomy tube 24 hours post ICU discharge and allow the track and skin to close. He will be brought back for his surgery in 1 to 2 months. An awake intubation could then be performed before induction of general anesthesia.

In summary, CICV is a rare but life-threatening situation that all anesthesia practitioners should be prepared to manage. If intubation fails and oxygenation cannot be maintained by bag-mask-ventilation despite a two-person technique, oropharyngeal, nasopharyngeal airways, and an EGD, an immediate decision should be made to perform a cricothyrotomy. Time and again, patients suffer hypoxic brain damage or death from a delayed decision to proceed with an infraglottic airway.

Every airway practitioner must be familiar with the cricothyrotomy equipment available locally and must acquire the necessary skills by performing cricothyrotomy on mannequins or cadavers so that emergency cricothyrotomy can be rapidly performed if required in the clinical setting.

It is better to have a live patient with a neck incision than a dead patient with a nice looking neck.