The effect of ventilation on systemic blood gases in the presence of left ventricular ejection during cardiopulmonary bypass.

The effect of pulmonary ventilation upon systemic arterial blood gases during cardiopulmonary bypass in the presence of left ventricular ejection was evaluated in 20 adult male patients undergoing coronary artery bypass grafting. Following rewarming, establishment of a sinus rhythm, and production of a pulse pressure of at least 20 mm Hg on the arterial pressure trace caused by left ventricular ejection, arterial blood gases were obtained from the arterial and venous extracorporeal circuits and the radial arterial cannula. Patients were then randomly assigned to a nonventilation (n = 10) or a ventilation (n = 10) group. The ventilation group was given 10 breaths/min with 100% oxygen at a tidal volume of 10 ml/kg. Whereas the nonventilation group received apneic oxygenation at zero end-expiratory pressure. After 5 minutes the arterial blood gas data were again obtained. Significant findings (p less than 0.05) included decreases in systemic carbon dioxide tension and increases in systemic pH in the ventilation group and decreases in systemic oxygen tension in the nonventilation group. Although the changes in the arterial blood gases were significant, these changes occurred well within the limits of clinical acceptability. It is concluded that left ventricular ejection for short periods during full cardiopulmonary bypass does not necessitate pulmonary ventilation.