Whether maintaining pulmonary nitrogenation and/or a stable ventilatory pattern during surgery would minimize changes in perioperative pulmonary function in two groups of patients with acute respiratory failure (ARF) whose lungs were being mechanically ventilated was examined. Group 1 (n = 39 cases) (inspired oxygen fraction [FlO2] <= 0.5, minute ventilation <= 15 1/min, peak inspiratory pressure <= 50 cmH2O, positive end-expiratory pressure [PEEP] <= 10 cmH2O) were assigned randomly to one of four intraoperative ventilator-gas mixture (FIO2 ~ 0.5) combinations: 1) Siemens 900C ventilator, N2/O2; 2) Siemens 900C ventilator, N2O/O2; 3) Ohio anesthesia ventilator, N2/O2; or 4) Ohio anesthesia ventilator, N2O/O2. Group 2 (n = 15 cases) (ventilatory requirements exceeding any of those in Group 1) had their lungs ventilated intraoperatively with the Siemens 900C ventilator and a gas mixture determined by their anesthesiologist (FIO2 ~ 0.6-1.0). In patients whose lungs were ventilated with the Ohio N2O/O2 combination, PaO2/FIO2 decreased significantly (P < 0.05) from 358 +/- 93 mmHg (mean +/- SD) preoperatively to 282 +/- 77 mmHg intraoperatively. The level of PEEP increased significantly from 5 +/- 3 cmH2O preoperatively to 9 +/- 4 cmH2O intraoperatively (P < 0.05). In patients whose lungs were ventilated with the Ohio N2/O2 combination, PaO2/FIO2 decreased significantly from 270 +/- 86 mmHg preoperatively to 174 +/- 74 mmHg intraoperatively. These variables did not change significantly in patients ventilated with the Siemens ventilator (groups 1 and 2). Pulmonary oxygen gas exchange returned to preoperative values by the first hour postoperatively. The authors conclude that intraoperative pulmonary oxygen exchange is better maintained in patients with ARF whose lungs are mechanically ventilated with the Siemens (a "critical care" type) ventilator, rather than the Ohio (an "operating room" type) ventilator. Maintaining pulmonary nitrogenation intraoperatively did not maintain pulmonary oxygen exchange better than did the N2O/O2 gas mixture. In patients with ARF, when the type of ventilator and ventilator settings are kept constant, anesthesia and surgery do not result in significant deterioration of pulmonary oxygen exchange perioperatively.
(C) 1989 American Society of Anesthesiologists, Inc.