Role played by oxygen in myocardial protection with crystalloid cardioplegic solution

To evaluate the importance of the oxygen dissolved in crystalloid cardioplegic solution, the protective effects of oxygenated glucose-insulin-potassium cardioplegic solution (O2-GIK) (oxygen tension greater than 600 mm Hg) on the isolated working guinea pig heart were compared with those of deoxygenated (N2-GIK) (oxygen tension less than 10 mm Hg) and aerated GIK solution (GIK) (oxygen tension = 140 to 160 mm Hg). Hearts were subjected to 180 minutes of ischemia with intermittent infusions (every 30 minutes) of cold cardioplegic solution, followed by 30 minutes of normothermic reperfusion. The O2-GIK solution tended to maintain high-energy phosphates at higher levels during ischemia, and resulted in the best recovery of cardiac function. Though not as effective as O2-GIK, GIK solution produced protective effects; N2-GIK solution failed to exert such effects. These results strongly suggest that the protective effects of crystalloid cardioplegic solution are due primarily to the oxygen dissolved in it; anaerobic metabolism or washout of the metabolites plays a minor part.