Effect of multidose cardioplegia and cardioplegic solution buffering on myocardial tissue acidosis

Multidose administration of cardioplegic solution during cardiac operation is intended to maintain both electromechanical arrest of the heart and myocardial hypothermia as well as to remove accumulated metabolites of anaerobic glycolysis. This study was conducted to assess the effect of multidose infusion of three different types of cardioplegic solution on tissue acidosis during global myocardial ischemia. Three groups of five dogs each were placed on cardiopulmonary bypass and the aorta was cross-clamped for 3 hours. The hearts were maintained at a constant temperature (20 degrees C) and cardioplegic solution was infused at an initial dose of 500 ml and five supplementary doses of 250 ml administered every 30 minutes. Group 1 received a crystalloid solution weakly buffered with sodium bicarbonate, Group 2 received a blood-based solution, and Group 3 received a crystalloid solution strongly buffered with histidine (Bretschneider's solution). The buffering capacities of the solutions used in Groups 2 and 3 were 40 and 60 times, respectively, that of the solution used in Group 1. The average myocardial tissue pH at the end of 3 hours of ischemia was 6.54 +/- 0.07 in Group 1, 7.23 +/- 0.05 in Group 2, and 7.19 +/- 0.06 in Group 3 (Group 1 significantly lower than Groups 2 and 3). Multidose infusion of a cardioplegic solution with low buffering capacity was unable to prevent the progressive development of tissue acidosis during 3 hours of ischemia. However, the multidose infusion of either blood-based or crystalloid solutions with high buffering capacity completely prevented any further reduction of tissue pH after the first 30 minutes of ischemia.