Chapter 92: Morbid Obesity

INTRODUCTION

The presence of obesity is determined by the body mass index (BMI), which can be calculated as follows:

A patient who weighs 75 kg and is 1.8 meters tall would have a BMI of 23.1 kg/m². Based on BMI, the patient can be classified as normal, overweight, obese, or extremely obese (Table 92-1). It should be noted that the term “morbid obesity” has been replaced by “extreme obesity.”

Obese patients are at increased risk for a variety of intraoperative and postoperative complications. In addition to BMI, waist circumference can be used as a predictor of increased risk. A waist circumference of 35 inches or greater in women or 40 inches or greater in men is associated with increased cardiovascular risk. Because obese patients present many challenges to anesthesiologists, an understanding of the pathophysiologic effects of obesity on anesthesia practice is imperative for safe practice.

AIRWAY CHANGES

Obese patients have an increased risk for difficult mask ventilation, direct laryngoscopy, and intubation due to increased tongue size, redundant oropharyngeal tissue, and a limited range of motion at the atlantoaxial joint due to accumulation of cervical adipose tissue. Presternal fat pads can also interfere with direct laryngoscopy, complicating airway management.

Preoperative airway assessment should be conducted with special attention paid to the Mallampati classification, neck circumference, thyromental distance, mouth opening, prognathism, and cervical range of motion. If the anesthesiologist is concerned that the patient will not be able to be safely intubated using direct or indirect laryngoscopy, the patient should be prepared for an awake fiber-optic intubation.

The likelihood of a successful direct laryngoscopy and intubation can be improved by ensuring the patient is in a head-elevated laryngoscopy position (HELP). To achieve this position, a ramp is formed under the patient’s upper back and cervical spine using blankets, pillows, or a commercially available device. The head is elevated above the hips with the neck extended. This ensures alignment of the external auditory meatus with the sternal notch, which compensates for the limited flexion caused by cervical adipose tissue.

Following induction of anesthesia, the pharyngeal muscles and tongue relax resulting in airway obstruction. A two-handed mask ventilation technique with a jaw thrust maneuver and the placement of an oral or nasal airway may be required to successfully mask-ventilate the patient. At the end of the surgery, care should be taken to not extubate the patient prematurely.

Many obese patients demonstrate signs and symptoms of obstructive sleep apnea (OSA) even if no formal diagnosis has been recorded. It is ...