[Effect of induced hypotension on arterial blood-gases]

Arterial blood-gases were evaluated before, during and after the vasodilator induced hypotension in patients undergoing mastectomy. Forty-two patients studied were anesthetized with halothane and nitrous oxide in oxygen. They were divided into following four groups according to vasodilators used: trimetaphan (TMP), nitroglycerin (TNG), adenosine triphosphate (ATP), and prostaglandin E1 (PGE1). Significant reduction in PaO2 was observed during induced hypotension in all groups. However, there was no difference in the degree of PaO2 decrease among four groups. A small but significant increase in PaCO2 and a decrease in pH were observed during and/or after hypotension with TNG and PGE1. These findings suggest that induced hypotension may impair the pulmonary gas exchange by decreased cardiac output and/or change in ventilation-perfusion ratio regardless of vasodilators used. Therefore, continuous arterial blood-gas monitoring should be desirable under these conditions.