Oxygenation of St. Thomas' Hospital cardioplegic solutions--effects of myocardial temperature and carbon dioxide

The effect of oxygenation of St. Thomas' Hospital cardioplegic solutions (ST solutions) was examined in isolated working rat hearts. They were subjected to hypothermic arrest (12 degrees C, 22 degrees C) for 3 hours with infusions of cardioplegic solutions repeated for 5 minutes every 30 minutes. Based on myocardial temperature and mode of oxygenation, the hearts were divided into six groups. Group I: 12 degrees C and non-oxygenated; Group II: 12 degrees C and 100%-oxygenated; Group III: 12 degrees C and 95% O2 + 5% CO2-oxygenated; Group IV: 22 degrees C and non-oxygenated; Group V: 22 degrees C and 100%-oxygenated; Group IV: 22 degrees C and 95% O2 + 5% CO2-oxygenated. The pH of ST solutions varied with the mode of oxygenation as follows: 7.9-8.2 in Groups I and IV; 8.7-8.9 in Groups II and V; 7.1-7.4 in Groups III and VI. In the two Groups (II and V) with 100%-oxygenated ST solutions, the functional recovery of the hemodynamic parameters was significantly inferior to that of Group I and III, VI with 95% O2 + 5% CO2-oxygenated ST solutions. It was concluded that 95% O2 + 5% CO2-oxygenated ST solutions were superior to 100%-oxygenated ones and the functional recovery at 22 degrees C of 95% O2 + 5% CO2-oxygenated ST solutions were comparable to that of non-oxygenated ones at 12 degrees C.