Fifty percent nitrous oxide depresses recovery from anoxic heart failure induced by 100% nitrous oxide.

In experiments on an isolated rate heart lung preparation, the effects of 100% oxygen, 50% nitrous oxide or air on myocardial metabolism during recovery from anoxic heart failure were evaluated with intramyocardial high energy phosphates, lactate and glycogen. A hundred percent nitrous oxide was administered until the cardiac output decreased from 30 to 20 ml/min, and then 50% nitrous oxide, air or 100% oxygen was administered. Fifty percent nitrous oxide reduced the cardiac output and caused heart failure again. The ATP level and energy charge in hearts with 50% nitrous oxide were significantly lower than those in the others. These data indicate that 50% nitrous oxide during recovery from anoxic heart failure had deleterious effects on myocardial function and metabolism.