ASSOCIATION FOR ACADEMIC SURGERY Postoperative Hypoxemia: Common, Undetected, and Unsuspected After Bariatric Surgery 1 Scott F. Gallagher, M.D., F.A.C.S.,* ,2 Krista L. Haines, M.A.,* Lynette G. Osterlund, M.D.,* Matt Mullen, B.S.,* and John B. Downs, M.D., F.C.C.M., F.C.C.P.† *Department of Surgery, USF Health, University of South Florida College of Medicine, Tampa, Florida; and †Department of Anesthesiology, University of Florida College of Medicine, Gainesville, Florida Submitted for publication July 9, 2009 Background. Patients undergoing gastric bypass are at greater than ordinary risk for postoperative respiratory insufficiency, presumably related to ob- structive sleep apnea (OSA) and patient-controlled an- algesia (PCA). This study was proposed to quantify the magnitude of the problem. Methods. Fifteen patients undergoing gastric by- pass had oxygen saturation (SpO 2 ) recorded continu- ously, but not displayed, for 24h postoperatively; eight also had arterial blood analysis every 4h. All received narcotic PCA. SpO 2 < 90% lasting more than 10 s was reviewed. Results are mean ± SEM. Results. Mean age was 44 ± 4 y, and mean BMI was 48 ± 2kg/m 2 ; 77% had OSA. Every patient had more than one episode with SpO 2 < 90% for longer than 30s undetected by routine monitoring; most had multiple episodes. Nadir SpO 2 averaged 75% ± 8%. Mean longest duration of desaturation below 90% averaged 21 ± 15min. Mean PaCO 2 was 37 ± 3mm Hg; maximum PaCO 2 was 47mm Hg. Conclusions. Severe and prolonged episodes of hypoxemia were a consistent finding, despite aggressive preoperative diagnosis and treatment of OSA, including use of CPAP postoperatively. Although some postopera- tive hypoventilation was expected, the degree and frequency of desaturation were surprising. No patient exhibited arterial PaCO 2 evidence of hypoventilation. No patient experienced cardiopulmonary arrest/insta- bility, in spite of severe, repeated episodes of hypox- emia. In no instance was a significant hypoxemic episode suspected or detected. Continuous pulse oximetry monitoring, with an audible alarm set for a sat- uration less than 90% for 10 s, would have alerted pro- viders to 100% of significant hypoxemic episodes. Our recommendation is routinely monitoring (with alarm capability enabled) every bariatric surgical patient, to prevent such occurrence. Ó 2010 Elsevier Inc. All rights reserved. Key Words: hypoxemia; hypoventilation; obesity; gas- tric bypass; bariatric surgery; obstructive sleep apnea; postoperative; pulse oximetry. INTRODUCTION Obesity has grown to epidemic proportions in this country. The National Health and Nutrition Examina- tion Survey revealed that at least one-third of the popu- lation is obese, i.e., exceed their ideal body weights by more than 20% [1]. Bariatric surgery for clinically sig- nificant obesity is common. Postoperatively, these patients present a higher risk for respiratory complica- tions than the normal weight population [2–4]. One such complication is hypoventilation, defined by decreased minute ventilation as a result of decreased rate and/or depth of respiration. Extremely obese individuals may exhibit evidence of chronic hypoventilation with mild hypercarbia in the resting, preoperative state [5, 6]. Postoperatively patients are at risk for hypoventila- tion secondary to respiratory depression and/or the inability to maintain an adequate airway [7, 8]. Respi- ratory depression may stem from impaired respiratory drive from residual volatile anesthetics, sedatives, or opioid analgesics [9]. Inadequate airway maintenance may develop due to decreased muscle tone from muscle relaxants, incomplete neuromuscular blockade 1 Presented at the 2008 Association for Academic Surgery–Aca- demic Surgical Congress in Huntington Beach, CA, and published as an abstract in the Journal of Surgical Research, 2008;144:370. 2 To whom correspondence and reprint requests should be ad- dressed at Department of Surgery, USF Health, University of South Florida College of Medicine, 1 Tampa General Circle, Suite F145, Tampa, FL 33606. E-mail: sgallagh@health.usf.edu. 0022-4804/09 $36.00 Ó 2010 Elsevier Inc. All rights reserved. 622 Journal of Surgical Research 159, 622–626 (2010) doi:10.1016/j.jss.2009.09.003