[Effects of hypothermia on cerebral oxygen metabolism in patients with mitral valve replacement]

To observe the effects of mild to moderate hypothermia on cerebral oxygen metabolism in patients with mitral valve replacement.

Twenty patients undergoing mitral valve replacement were randomly divided in mild (30 ) and moderate (26 degrees Celsius) hypothermia groups. Under alpha stat, the oxygen content and the concentration of lactic acid in the radial artery and jugular venous bulb were monitored in patients undergoing mitral valve replacement at mild and moderate hypothermia respectively. The arterial-venous difference of oxygen content, oxygen uptake rate, and blood lactic acid levels in the cerebrum and total body were calculated. The effect of cardiopulmonary bypass (CPB) under the two hypothermia strategies on cerebral oxygen metabolism was analyzed.

In the two groups, arterial-venous differences and oxygen uptake rates were both decreased after the commencement of cardiopulmonary bypass, and were rapidly elevated during rewarming. In mild hypothermia group, the arterial-jugular venous difference and oxygen uptake were higher than those in moderate hypothermia group (P<0.05) during CPB when the lowest temperature was reached. The concentration of lactic acid in the plasma was progressively increased in both groups during CPB. Arterial-venous difference in the oxygen content in both groups was still lower during CPB than before CPB(P<0.01).

Mild and moderate hypothermia during CPB is sufficient to retain the balance of cerebral oxygen metabolism, and more intensive hypothermia may not ensure better cerebral protective effect. Cerebral oxygenation progressively increases after CPB under hypothermia, but whether imbalance of cerebral oxygen metabolism occurs needs further investigation.