A preliminary study of the optimal anesthesia positioning for the morbidly obese patient.

BACKGROUND: Hypoxemia during the induction of general anesthesia for the morbidly obese patient is a major concern of anesthesiologists. The etiology of this pathophysiological problem is multifactorial, and patient positioning may be a contributing factor. The present study was designed to identify optimal patient positioning for the induction of general anesthesia that minimizes the risk of hypoxemia in these patients.

METHODS: 26 morbidly obese patients (body mass index-BMI 56 +/- 3) were randomly assigned to one of three positions for induction of anesthesia: 1) 30 degrees Reverse Trendelenburg; 2) Supine-Horizontal; 3) 30 degrees Back Up Fowler. Mask ventilation, full neuromuscular paralysis and direct laryngoscopy were performed. Any airway difficulties were noted. After endotracheal tube placement, subjects were ventilated for 5 minutes with 1% isoflurane in a mixture of 50% oxygen/50% air and then disconnected from the ventilation circuit. The time required for capillary oxygen saturation (SaO2), as measured by pulse oximeter, to decline from 100% to 92% was noted and identified as the safe apnea period (SAP). Ventilation was then immediately re-established. The lowest SaO2 after resuming ventilation and the time from that nadir to an SaO2 of 97% were also recorded.

RESULTS: BMI and hip-waist ratios of patients in groups 1, 2 and 3 did not significantly differ. There were no differences in airway difficulties between the different groups. The SAP in groups 1, 2 and 3 was 178 +/- 55, 123 +/- 24 and 153 +/- 63 seconds, respectively. The SaO2 of patients in the reverse Trendelenburg position dropped the least and took the shortest time to recover to 97%.

CONCLUSIONS: In morbidly obese patients, the 30 degrees Reverse Trendelenburg position provided the longest SAP when compared to the 30 degrees Back Up Fowler and Horizontal-Supine positions. Since on induction of general anesthesia morbidly obese patients may be difficult to mask ventilate and/or intubate, this extra time may preclude adverse sequelae resulting from hypoxemia. Therefore, Reverse Trendelenburg is recommended as the optimal position for induction.