As the number of obese individuals in the United States continues to rise, the likelihood of encountering morbidly obese patients in the operating room, as well as the number of bariatric procedures, will predictably increase. Recent data has shown that 1 in 4 residents of the United States are classified as obese, which has increased approximately 24% since 2000.¹ The same study noted that individuals classified as morbidly obese, with a BMI over 50, showed the greatest percentage increase of prevalence between 2000 and 2005, rising more than 50%.¹ Data released in 2007 has shown that the number of bariatric procedures performed in the United States was expected to increase over 10-fold from 13,000 procedures in 1998 to 200,000 procedures in 2006, paralleling the significant rise in obese individuals.² Management of the airway of obese patients often presents challenges to the anesthesiologist while in the operating room. The increased difficulty, secondary to increased soft tissue on the patient’s chest or in the airway, often complicates ventilation and/or laryngoscopy. In addition to the decreased chest wall and lung compliance that typically occurs during general anesthesia, many bariatric procedures are performed laparoscopically, which dictates the need for positive pressure ventilation via an endotracheal tube, with a further reduction in compliance. For these reasons, it is essential that all anesthesia providers become experts in the management of the airway in obese patients. In general, much of the difficulty in securing the airway of a morbidly obese patient involves management of the anatomic and physical challenges that are present secondary to the increased amount of adipose tissue and its related effects on the airway and lung volumes.

Although the exact definition is debatable, morbid obesity is commonly defined as a BMI greater than 40 kg per m2. These patients typically manifest an increased amount of adipose tissue on their anterior chest, causing decreased chest wall and lung compliance. This results in a greatly reduced functional residual capacity (FRC), especially when the patient is placed in the supine position. Positioning a patient in the head-elevated position (ie, ear aligned with sternal notch) as opposed to the supine position results in a 23% increase in arterial oxygen tension and a 29% increase in time to desaturation after 3 minutes of preoxygenation.³ These increases are thought to be a direct result of increased FRC and an increase of oxygen reserve during the apneic period prior to intubation.

In addition to an increased amount of adipose tissue on their anterior chest, morbidly obese patients have an increased amount of subcutaneous adipose tissue on their anterior and posterior neck leading to decreased anterior mobility of pharyngeal structures and to decreased neck extension during laryngoscopy, respectively. Lastly, it has been shown that there is an increased amount of submucosal tissue in the oral cavity and pharynx of obese patients. This increased tissue can result in an enlarged tongue, increased size of the tonsillar pillars, and encroachment of the posterior pharyngeal wall into the pharyngeal space with an increase in both Mallampati class and Cormack-Lehane grade view (see also Chapter 51).⁴ The body habitus, as opposed to the absolute weight of the patient, is a more predictive factor in determining the difficulty with intubation and ventilation.⁴ An android body habitus with more abdominal adipose tissue, as opposed to a gynecoid body habitus with more hip and buttock adipose tissue, will typically cause a greater decrease in lung compliance in the supine position secondary to increased pressure on the diaphragm during inspiration. This can lead to even less effective preoxygenation and increased airway pressures during ventilation after that patient has been intubated.

Recently, attention in the literature has focused on whether obese patients actually present an increased risk of difficult ventilation or intubation. A study by Juvin et al⁵ in 2003 concluded that obese patients were more difficult to intubate as compared with nonobese patients. The authors reported an increase in multiple attempts at intubation and a decreased Cormack-Lehane grade with direct laryngoscopy of obese patients.⁵ In contrast, the authors of a recent study found that, after intubating 100 morbidly obese patients presenting for bariatric surgery, there was no relation between patient weight and difficulty with intubation.⁶ In this investigation, only Mallampati class and neck circumference were predictive of difficulty with intubation.⁶ More recently, a study by Gonzalez et al,⁷
in which obese and nonobese patients were compared, found that obese patients were several times more likely to have an intubating difficulty score greater than 5 and were therefore classified as difficult to intubate. The authors further showed that a relationship exists between difficulty of intubation in an obese patient and an increased neck circumference, or a Mallampati class of 3 or greater (Fig. 52-1