Intraoperative arterial oxygenation in obese patients

Although obese patients have been shown to represent a particularly high risk group with respect to hypoxemia both pre and postoperatively, no data exist to delineate the intraoperative arterial oxygenation pattern of these patients. Furthermore, no one has studied the effects of a change in operative position or a subdiaphragmatic laparotomy pack on arterial oxygenation (PaO2). Sixty-four adults undergoing jejunoileal bypass for morbid exogenous obesity, with a mean weight of 142.0 +/- 31.4 kg and a mean age of 33.3 +/- 10.4 years, were studied. Twenty-five patients (Group I) were maintained in the supine position throughout the operative procedure, while the remaining 39 patients (Group II) were changed to a 15 degrees head down position 15 minutes after a control blood sample was taken. Four additional markedly obese patients were studied to determine the effect of an abdominal pack of PaO2 values. The following findings were demonstrated: 1) 40% oxygen did not uniformly produce adequate arterial oxygenation for intra-abdominal surgery in otherwise healthy obese patients; 2) placement of a subdiaphragmatic abdominal laparotomy pack without a change in operative position resulted in a consistent fall in PaO2 in each patient to less than 65 mm Hg even though 40% oxygen was being administered; and 3) a change from supine to a 15 degrees head down operative position resulted in a significant (P less than 0.001) reduction in mean PaO2 (73.0 +/- 26.3 mm Hg). Seventy-seven per cent of these patients demonstrated PaO2 values of less than 80 mm Hg on 40% oxygen. Because of these findings, serious consideration should be given to the routine use of the Trendelenberg position intraoperatively in obese patients. However, if one elects this posture, prudence would dictate careful monitoring and maintenance of arterial oxygenation. Certainly, in obese patients, the intraoperative combination of the head down position and a subdiaphragmatic laparotomy pack should be avoided. In addition, since our data were collected in obese but otherwise healthy, young patients free of cardiorespiratory disease, special attention should be directed at the continuous measurement of arterial oxygenation in the older obese patient with either intrinsic dysfunction of vital organs (heart, lung, liver, kidney) or surgical disorders (peritonitis, sepsis).