Effect of hypocapnia on arterial oxygenation during induced hypotension]

We evaluated the effects of hypocapnia on arterial oxygenation during induced hypotension with nitroglycerin (TNG) or prostaglandin E1 (PGE1) in patients undergoing mastectomy. Of the 20 patients studied, 10 belonged to TNG group and 10 belonged to PGE1 group. Mean arterial pressure during induced hypotension was maintained at 70% of the values observed before hypotension. A significant decrease in PaO2 was observed during hypotension under normocapnia (PaCO2 35-40 mmHg) in both groups. In addition, small but significant reduction in PaO2 from 128.5 +/- 23.7 mmHg to 122.5 +/- 25.5 mmHg in TNG group and from 129.9 +/- 11.9 mmHG to 116.7 +/- 15.6 mmHg in PGE1 group were induced by hypocapnia (PaCO2 27-30 mmHg) during hypotension. These findings suggest that usual dose of TNG and PGE1 might not or might partially inhibit hypoxic pulmonary vasoconstriction.