The effect of obesity and anesthetic maintenance regimen on postoperative pulmonary complications.

Results from the 2007 to 2008 National Health and Nutrition Examination Survey estimate that, among adults in the United States, 68% are either overweight or obese (body mass index [BMI] 25 kg m ), with the prevalence having increased significantly over the past 20 years. The associated health problems mean that this population is presenting for surgery in ever greater numbers. The challenges regarding the perioperative management of obese patients are well known, with the effects of obesity on the airway and the respiratory, cardiovascular, and gastrointestinal systems being of most concern to anesthetists. In 1987, Strandberg and colleagues found a correlation between obesity and the area of lung densities seen immediately after induction of anesthesia. A more recent study showed that during general anesthesia, morbidly obese patients suffer more atelectasis than did the nonobese, and unlike the normal population, this atelectasis can persist for 24 hours. Atelectasis may result in arterial hypoxemia and marked alterations in respiratory mechanics, which can be alleviated by the use of positive end-expiratory pressure during anesthesia. Applying 10 cm H2O of positive endexpiratory pressure increases oxygenation in obese patients, and this improvement is directly related to the amount of alveolar recruitment achieved. However, lung recruitment maneuvers do not improve postoperative oxygenation, and thus rapid recovery from general anesthesia is desirable to minimize postoperative respiratory complications. Agents of choice for rapid emergence and recovery in recent times have been IV propofol, owing to its large volume of distribution at steady state and high metabolic clearance, or the less-soluble volatile anesthetic, desflurane. However, confusion persists regarding drug dosing in the obese, largely because of inadequate knowledge of pharmacokinetic parameters with altered body composition. Volume of distribution, clearance, and protein binding may each be affected by obesity. Clinical studies have, so far, failed to define a universal size descriptor suitable for use in the obese population; therefore, titration to clinical end-points or targeted, processed, electroencephalogram (EEG) values such as bispectral index (BIS) remain advisable. In this edition of Anesthesia & Analgesia, Zoremba and colleagues report on the effects of propofol and desflurane on postoperative lung function in overweight patients, concluding that maintenance of anesthesia with propofol impairs early postoperative lung function and pulse oximetry values to a greater extent than does maintenance with desflurane. Furthermore, the reduction in pulmonary function at 2 hours appeared to increase with increasing obesity after propofol but not with desflurane anesthesia. These findings, on the face of it, seem somewhat surprising, given what is known of the pharmacokinetics of propofol. However, previous work has suggested that desflurane may have a better recovery profile than does propofol in morbidly obese patients with regard to early recovery parameters including eye opening, orientation, postextubation Spo2 values, and sedation up to 2 hours after surgery. 8