Today more than 30% of adults in the United States are obese, and it is estimated that by the year 2025 that number will exceed 40%. Obesity is not confined to industrialized, developed nations like the United States, but has become a worldwide problem of epidemic proportions. There is no precise definition of when obesity actually begins. A patient is considered obese when the amount of body fat increases beyond the point where health deteriorates and life expectancy is shortened. The precursors of obesity include gender, genetic and environmental effects, ethnicity, education, and socioeconomic status. In industrialized countries obesity is more common in the lower socioeconomic groups, while in developing countries it is often associated with affluence.
Obesity affects every organ system and is the cause of many chronic medical problems. Obese patients have more annual admissions to the hospital, more outpatient visits, and higher prescription drug costs than nonobese adults. Obese patients also have “quality of life” issues than can include depression and a feeling of social incompetence. In 1991 the United States’ National Institutes of Health Consensus Development Conference Panel recommended weight reduction surgery as the best alternative for extreme obesity for patients unable to lose weight by diet and exercise. Most of the medical conditions associated with extreme obesity are reversible following sustained surgical weight loss.
The number of bariatric surgical procedures performed in the United States in 2005 is estimated to have exceeded 150,000. Laparoscopy is now the preferred surgical approach since it is minimally invasive and allows high-risk morbidly obese patients to recover more rapidly with fewer complications than following open procedures.
This chapter will discuss anesthetic considerations for the obese patients undergoing bariatric surgery.
Body mass index (BMI), an indirect measure of obesity, is calculated by dividing patient weight (kilograms, kg) by the square of their height (meters, m). BMI = kg/m2. An individual with a BMI ≥ 30 kg/m2 is said to be obese. “Morbid” obesity describes obesity that, if untreated, will significantly shorten life expectancy. A variety of definitions exist, but any patient with a BMI ≥ 40 kg/m2 is considered to be “morbidly” obese. A patient with a BMI ≥ 35 kg/m2 who has serious medical comorbidities is also a candidate for weight loss surgery.
Since most anesthetic drugs are administered on the basis of either ideal body weight (IBW), lean body weight (LBW), or total body weight (TBW), the anesthesiologist must be familiar with these terms as they pertain to the obese patient.
IBW is a measure initially derived by life insurance companies to describe the weight statistically associated with maximum life expectancy. In the absence of weight tables, IBW can be easily estimated by the simple formula IBW = 22 × (h × 2), where ‘h’ is the patient's height.1 Normal weight ranges between ±10% of IBW.