Anesthetic Pharmacology and the Morbidly Obese Patient
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ANESTHETIC PHARMACOLOGY (AG DOUFAS, SECTION EDITOR)
Anesthetic Pharmacology and the Morbidly Obese Patient Jerry Ingrande • Hendrikus J. M. Lemmens
Published online: 13 December 2012 Springer Science + Business Media New York 2012
Abstract Anesthesiologists are increasingly being faced with treating obese patients. Physiologic and anthropometric changes associated with obesity—most notably increases in cardiac output, changes in tissue perfusion and increases in total body weight, lean body weight, and fat mass affect the pharmacokinetics (PK) of anesthetic agents. In addition, redundancy of airway tissue, obstructive and central sleep apnea and CO2 retention affect the pharmacodynamics (PD) of anesthetics and narrow the therapeutic window of numerous anesthetic drugs. Safe and effective pharmacologic management of the obese patient requires a thorough understanding of how obesity affects the PK and PD of anesthetics. Keywords Obesity Pharmacokinetics Pharmacodynamics Total body weight Lean body weight Volume of distribution Clearance Cardiac output Distribution Peak effect Elimination Half-life
Introduction The prevalence of obesity among adults in the United States is increasing. According to the Centers for Disease Control and Prevention, more than one-third of U.S. adults are obese (35.7 %) [1]. In addition, the incidence of obesity
J. Ingrande (&) H. J. M. Lemmens Department of Anesthesia, Stanford University School of Medicine, 300 Pasteur Drive Room H3580, Stanford, CA 94305, USA e-mail: [email protected] H. J. M. Lemmens e-mail: [email protected]
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has increased dramatically over the last decade. By 2010, the number of states with an obesity rate of 30 % or more had risen to twelve. By comparison, in the year 2000, no state had an obesity rate greater than 30 % [2]. Obesity and the length of exposure to obesity have been shown to be risk factors for both number of hospital admissions and length of hospital stay [3, 4]. In 1998, the National Institutes of Health recommended bariatric surgery as the primary treatment of morbid obesity [5]. Since then, the number of bariatric surgeries has increased dramatically, although this amount has plateaued since 2006 [6]. Anesthesiologists are now managing obese patients—and their associated comorbidities—at an increasing rate. The increased risks of anesthesia in obese subjects have been described [2, 7, 8]. The physiologic and anthropometric changes associated with obesity likely affect the pharmacokinetics (PK) of anesthetic agents [9]. Obesity is associated with an increase in cardiac output and in total blood volume, which may alter drug distribution, peak concentration and clearance [7, 9]. In addition, increases in fatand lean-body mass and changes in tissue perfusion may affect the apparent volume of distribution of many anesthetic agents. Pathophysiology associated with obesity, including an increased prevalence of obstructive sleep apnea and CO2 retention, reduced functional residual capacity, and cardiac dysfunction, al
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