The Case

A 34-year-old morbidly obese man weighing 178 kg (392 pounds) was admitted for incision and drainage of a pilonidal abscess with fistulectomy under general anesthesia. He reported no major medical problems and no history of snoring. Upon initial evaluation by an anesthesiologist, he was found to have a short thick neck and a Mallampati score of 3, suggesting that endotracheal intubation might be difficult.

The patient was positioned supine with his head and neck in the ramped position plus sniffing position for endotracheal intubation. A high flow nasal cannula was used for preoxygenation and to help avoid precipitous desaturation in the event of difficulty intubating the trachea. A fellow anesthetist suggested that video-laryngoscopy equipment should be brought into the operating room, but the anesthesiologist assigned to the case rejected the suggestion. Anesthesia was induced with intravenous propofol and fentanyl, while neuromuscular block was obtained with intravenous suxamethonium. A first-year resident attempted to intubate the patient but failed. The attending anesthesiologist took over, but before intubation could be performed, the patient started to cough and desaturated to 40-50%. The anesthesiologist gave the patient rocuronium and sevoflurane, but he still could not intubate the patient and failed with a glide scope. He then gave 12 mg/kg of intravenous sugammadex to reverse the neuromuscular block. After about two minutes, the patient started to cough up bloody secretions and was administered 100% oxygen by mask. His arterial saturation increased rapidly to 100%.

Although the patient's saturation was less than 80-88% for at least 10 minutes, he suffered no apparent neurological sequelae. After a period of recovery, he was brought back to the operating room for the originally scheduled procedure, which was completed without further complications.

The Commentary

By Christian Bohringer MD

Background

Difficult intubation is still a significant problem in current clinical anesthesia practice. When it is associated with impaired ventilation and inadequate brain oxygenation, it can lead to brain damage within just a few minutes. Even though this problem occurs rarely, brain damage and death attributed to difficult airway management are a major cause of anesthesia malpractice claims.¹ Etiological factors that contribute to the occurrence of hypoxic ischemic encephalopathy in this setting include inadequate preoperative assessment of the patient’s airway, inadequate preparation, lack of advanced airway equipment, and lack of team experience using such equipment. Patient factors, such as morbid obesity with sleep apnea and anatomic narrowing of the airway due to tumors or acute neck hematomas with concurrent acute airway obstruction, are also frequent contributors to the problem of difficult intubation (for additional factors contributing to difficult mask ventilation or intubation, please refer to Tables 1 and 2 in a prior WebM&M commentary). The primary responsibility for ensuring the adequacy of the patient's oxygenation and ventilation during any surgical procedure lies with the anesthesiologist.²

This morbidly obese patient was correctly identified in the preoperative period as having a high risk for developing hypoxemia during endotracheal intubation. Trying to predict the degree of difficulty with intubation is always of paramount importance during the preoperative assessment. However, it is important to recognize that preoperative physical assessment of the airway has a low positive predictive value for anticipating a difficult intubation. Anesthesiologists should therefore not be lulled into a false sense of security and complacency by the absence of warning signs like limited mouth opening, a short thyromental distance and limited neck movement.

The Mallampati score when used in isolation as the only predictor has been repeatedly shown to have low sensitivity and specificity for predicting difficult intubation.³ In the largest single study of adults receiving general anesthesia, with over 102,000 patients, the Mallampati score only had a sensitivity of 45% and a specificity of 89%.⁴ Even when multiple physical examination findings are assessed in combination, only about half of difficult intubations are predicted by a standard airway exam.^5,6 Reliable bedside criteria to predict difficult intubation therefore remain elusive to this day.⁷ For patients who have had prior general anesthesia, a history of difficult prior intubation may be a better predictor than the airway examination.

Approach to Improving Safety

Unfortunately, the difficulty of endotracheal intubation was underestimated in this case and advanced airway equipment, such as a video-laryngoscope and a flexible bronchoscope, were not available in the operating room during the induction of anesthesia. The use of a video-laryngoscope in combination with a flexible bronchoscope has been found to be very successful in managing the difficult airway.⁸ The combination of these devices can also help to prevent airway trauma, which is unfortunately still a common complication of difficult intubations. From a patient safety perspective, if both devices had been present during induction, an anesthesiologist with experience using them would probably have achieved successful intubation without hypoxemia.

In this case, the patient became hypoxic during attempted intubation and the equipment that could have rectified this situation had to be transported to the operating room. This delay then caused the anesthesia team to persist with further unsuccessful attempts at intubation via direct laryngoscopy. These attempts resulted in the patient salivating and bleeding; he then aspirated blood and coughed up bloody secretions. One of the issues with not having advanced airway equipment in the operating room is that the anesthesia team cannot leave the apneic patient to gather this equipment, while ancillary staff may not know which equipment to get and where it is stored. This situation often results in a significant delay before life-saving airway equipment arrives in the operating room. Therefore, it is prudent to err on the side of caution and have advanced airway equipment readily available before inducing anesthesia. Anesthesiologists need to focus just as much on the ready availability of advanced airway equipment in the operating room prior to induction as on preoperative airway assessment. Health care systems and hospitals must be willing to pay for an adequate supply of these advanced airway management devices so that anesthesia can be provided safely without any unnecessary delays because necessary equipment is in storage or in use in another room.

Several other aspects of this case merit discussion. First, it was very appropriate to administer high flow nasal oxygen during the induction of anesthesia and the intubation attempt. The highest priority during airway management is always to ensure adequate oxygenation of the brain to prevent the complication of hypoxic ischemic encephalopathy. High flow nasal oxygen has been shown to significantly prolong the time to desaturation during apnea and is recommended during the management of a difficult airway.⁹ High flow nasal oxygen is equally useful during an attempt at awake intubation because even awake intubation can be complicated by episodes of hypoxemia.

Second, an experienced practitioner should generally make the first attempt at intubation in a high-risk patient as in this case. Letting a junior resident attempt a conventional direct laryngoscopy in this high-risk scenario was, in retrospect, not the most prudent course of action due to the airway trauma and hypoxemia that resulted. Anesthesiology academic programs lack standardization in the roles of residents and fellows. Woodworth et al  recently introduced the concept of entrustable professional activities (EPAs), a workplace-based method to assess the achievement of competency milestones at the point-of-care in anesthesiology training.¹⁰ EPAs allow for practitioners to determine when residents can perform procedures in specific scenarios.

Third, awake intubation with a flexible bronchoscope, a video-laryngoscope or a combination of the two should have been considered in this Case. Obese patients desaturate quickly because of their reduced functional residual capacity.^11,12 Apnea is not required with awake intubation, which makes life-threatening desaturation much less likely during the intubation process. Therefore, anesthesiologists should have a low threshold for managing the airway of a morbidly obese patient via awake intubation with a flexible bronchoscope. Hypoxemia can, however, still occur during awake intubation and the team must always be prepared to perform an emergent cricothyroidotomy, even when the plan is to intubate the patient awake.

Fourth, allowing the patient to wake up from anesthesia after reversing rocuronium-induced neuromuscular blockade with high dose sugammadex was an essential step that prevented hypoxic brain injury. Whenever adequate oxygen saturation cannot be maintained under anesthesia, the anesthesia either needs to be rapidly reversed to allow for spontaneous respiration or a surgical airway needs to be created. Performing surgical cricothyroidotomy in a morbidly obese patient without inducing hypoxic brain damage is significantly more difficult than in a patient with normal body habitus. The increased neck adipose tissue makes it more difficult to identify airway structures and to locate the cricothyroid membrane. In this case, rapid reversal of neuromuscular blockade made surgical cricothyroidotomy unnecessary, preventing hypoxic brain injury.

Additionally, many operations can be performed under local anesthesia with a regional nerve block, a spinal or an epidural block. Endotracheal intubation can often be avoided with these types of anesthetics as long as the operation is completed before the local anesthetic block has worn off. This patient’s morbid obesity made management with regional anesthesia infeasible for this operation. The lithotomy and head down (Trendelenburg) position required for excision of the pilonidal sinus leads to atelectasis and hypoxemia in a spontaneously breathing obese patient. Obese patients usually do not tolerate the Trendelenburg position well when they are awake. Anesthesiologists therefore prefer to intubate morbidly obese patients so that they can counterbalance the atelectasis induced by abdominal contents displacing the diaphragm in a cephalad direction with the positive end expiratory pressure (PEEP) exerted on the lungs by the ventilator.^13,14 It is highly likely that this patient would not have tolerated a spinal anesthetic while lying in a head-down position. Intubating a patient emergently in the lithotomy position is even more difficult than in the supine position because it is difficult to achieve an adequate sniffing position that aligns the oral, pharyngeal and laryngeal axes while the legs are up in stirrups. Managing this patient with general anesthesia and endotracheal intubation was therefore a reasonable plan of action for this operation.

Fifth, an interesting aspect of this case is that a colleague suggested the use of video-laryngoscopy equipment. This behavior is an example of a Safety-II activity. Safety-I involves the active detection of error to prevent future errors from happening using preventative methods. Safety-II activities are performed by frontline personnel, often in times of uncertainty and stress, to prevent errors before they happen. Safety-II behaviors are a component of resilient systems, characterized by teamwork, focused communication, and redundancy.  Although we do not know the details of the conversation, it is possible that the colleague was raising the issue regarding the lack of onsite necessary equipment for high risk patients, which is a system issue and not a critique of the attending. System issues are often latent factors that are difficult for frontline personnel to change and may be viewed as “one of the holes in the Swiss cheese model” that could line up with other holes in future, leading to a more serious outcome. 

In summary, high-risk morbidly obese patients should be managed by experienced anesthesia practitioners who are well-prepared and facile with the use of advanced airway equipment. Advanced airway management devices should be present in the operating room prior to induction of anesthesia whenever possible. High flow nasal oxygen is of great benefit when intubating obese patients, and in the postoperative period, when it can be used to prevent hypoxia in patients with sleep apnea. There should be a low threshold for awake intubation in morbidly obese patients because they are harder to oxygenate under general anesthesia and they are more likely to become hypoxic if there is any delay during endotracheal intubation. Performing a rescue cricothyroidotomy in time to prevent hypoxic ischemic encephalopathy is also more difficult in this group of patients than in patients with normal body habitus. Morbidly obese patients are at high risk for hypoxemia in the perioperative period, and they need to be treated with special precautions to prevent bad outcomes.

Take Home Points

• The preoperative airway exam is fallible – only about half of difficult intubations are predicted by a standard airway assessment.
• High flow nasal oxygen can help to prevent hypoxemia in the perioperative period.
• Obese patients may be difficult to oxygenate under general anesthesia.
• Advanced airway management devices should be readily available during induction of anesthesia in all high-risk patients (including obese patients and patients with distorted airway anatomy).
• High risk patients should be managed by experienced anesthesia providers.
• There should be a low threshold for performing an awake intubation whenever difficulty with intubation or oxygenation is anticipated.
• Anesthesia care providers need to be facile with the use of advanced airway management devices.

Christian Bohringer, MBBS
Professor of Clinical Anesthesiology
Department of Anesthesiology and Pain Medicine
UC Davis Health
Chbohringer@ucdavis.edu

References

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