Difficulty with mask ventilation, rapid oxygen desaturation, and altered pharmacokinetics can make airway management challenging.45 Impedance to airway management is caused by excess fatty tissue externally on the breast, neck, thoracic wall, and abdomen and internally in the mouth, pharynx, and abdomen. The respiratory compromise that is associated with morbid obesity leaves little room for error.
Patients who are obese have increased intra-abdominal pressure and increased incidence of hiatal hernia and gastroesophageal reflux disease. These characteristics render patients more prone to aspiration during airway management.46
Patients who are obese will desaturate more rapidly after preoxygenation than their lean counterparts. When no cervical spine injury is suspected, desaturation may be partially prevented by keeping the patient in a 25-degree head-up position during preoxygenation.47
Two-person bag-valve mask (BVM) with a two-handed bilateral jaw thrust is recommended in patients who are morbidly obese. If tolerated, an oral airway may be used to prevent the tongue from occluding the airway. The early use of noninvasive positive-pressure ventilation may abate the need for endotracheal intubation. High expiratory positive pressures may be needed.
Obesity is not a contraindication for rapid sequence intubation. Advance preparation is critical, and assessment for a potential difficult airway is of utmost importance.48
The "sniffing" position results in suboptimal positioning for laryngoscopy in patients who are obese, and this may also confound results and falsely worsen graded views.49 The "ramping" position (Figure 298-3A) offers improved intubation conditions in patients who are morbidly obese compared to the "sniffing" position (Figure 298-3B). This position is achieved by placing multiple folded blankets under the upper body, head, and neck until the external auditory meatus and the sternal notch are horizontally aligned.50
The ramping position (A) is more effective for intubation than the sniffing position (B) in patients with morbid obesity.
First give consideration to awake intubation, given that patients who are obese may be difficult to mask ventilate and rapid oxygen desaturation may occur after the ablation of spontaneous ventilation, especially in patients with a BMI greater than 40 kg/m2.51,52,53 The awake intubation may be performed either by the nasotracheal or orotracheal routes.
The relative benefits and risks of the awake intubation approach must be weighed against the merits of rapid sequence intubation, which reduces risk of aspiration, improves intubating conditions, and results in easier insertion of advanced and rescue airway devices. During rapid sequence intubation, the chance for first-pass success can be optimized by video laryngoscopy. The intubating laryngeal mask airway is effective in obesity and should be readily available because surgical access to the airway may be difficult. The bougie is a good rescue device.54
Percutaneous and open surgical access to the airway may be difficult when landmarks are obscured by excess soft tissue and a short neck in the "cannot intubate, cannot ventilate" scenario.55 Obesity and a short neck are associated with difficult transtracheal needle ventilation and retrograde tracheal intubation.56,57 However, in the elective surgical airway management setting, cricothyroidotomy is technically feasible even in patients with difficult neck anatomy caused by obesity.58 Unfortunately, the luxury of a controlled environment is often not an option for the emergency physician.
Until the proper size tracheostomy tube is located, a 6-mm-inner-diameter endotracheal tube passed through a cricothyroidotomy incision may serve as a temporizing measure.59 There is limited literature concerning the success rates of surgical airways in patients in the emergency setting. Even in an ideal setting, cricothyroidotomy requires more than 100 seconds to achieve ventilation,57 and the procedure is rarely performed in the ED.60
With respect to ventilator management, adjust tidal volume as per body weight and initially keep it at 8 mL/kg of ideal body weight in patients in whom mechanical ventilation is necessary, but patients with acute respiratory distress should be ventilated with much lower tidal volume. Lower tidal volumes can be compensated for by increasing the respiratory rate to maintain normal minute ventilation and thus avoiding hypoxemia and hypercarbia.61 During prolonged ventilation, ventilatory settings are determined by serial measurements of arterial blood gasses and peak airway pressures.62