The effects of tidal volume and end expiratory pressure on pulmonary gas exchange during anesthesia

Abstract

Thirty supine adult patients undergoing general anesthesia for operations on the periphery or lower abdomen were studied to determine the relative merits of mechanical ventilation with a small tidal volume, a small tidal volume with continuous positive pressure, and a large tidal volume. Alveolar arterial oxygen tension difference (A aD(O2)) improved when continuous positive pressure or large tidal volume ventilation replaced small tidal volumes, and when large tidal volume ventilation replaced continuous positive pressure ventilation with a small tidal volume. The largest changes A aD(O2) occurred in obese patients and in those with high mean A aD(O2)'s. A small overall improvement in A aD(O2) was noted with time, regardless of the order of delivery of ventilatory patterns. V(D)/V(T) was greatest when positive end expiratory pressure was applied and lowest with large tidal volume ventilation. Static lung compliance was highest with large tidal volume ventilation. These findings suggest that optimum pulmonary gas exchange in the supine position is produced by large tidal volume ventilation.