Study to Determine Incidence of Hypoventilation in Patients Who Have Undergone Gastric Bypass

We propose to determine if patients with clinically significant obesity (body mass index, BMI, between 40 kg/m2 and 85 kg/m2), who have undergone gastric bypass procedures under general anesthesia hypoventilate during the initial twenty-four hour postoperative period, and if so, to what degree. Adequacy of ventilation will be assessed by serial arterial blood analyses. Patients will be monitored for SpO2 in the preoperative holding area, in the operating room, and the post-anesthesia care unit (PACU) by conventional and study pulse oximeters. SpO2 data will be collected continuously and recorded on the study pulse oximeter for the entire study period. Arterial blood samples will be drawn for analysis every four hours by in-dwelling arterial catheter, using standard sterile technique. Hypoventilation is defined as an increase in PaCO2 five or more mm Hg above patient's baseline.