Blood Cardioplegia Serves as a Bicarbonate Donor to the Myocardium during Ischemia: Effects of Anoxia and Hypercapnia on Acid-Base Characteristics of Blood Cardioplegic Solution

Abstract

Objectives: We investigated the alterations of acid-base characteristics of the blood cardioplegia (BCP) solution during aortic cross-clamping in hearts arrested with BCP and during in vitro-simulated ischemia. Methods: Following aortic cross-clamping, the hearts of 40 patients undergoing cardiac surgery were intermittently infused with an 18°C BCP solution and finally with a 34°C BCP solution prior to aortic cross-clamp release. We measured the pH, partial CO₂ pressure (pCO₂), [HCO₃^–], and [Cl^–] of the coronary sinus effluent in the final BCP solution. The BCP solution was assessed under in vitro gassing at 34°C with 95% N₂ + 5% CO₂ (n = 6), 50% N₂ + 50% CO₂ (n = 3), or 100% CO₂ (n = 6). Results: The coronary sinus effluent, compared with the preinfusion BCP solution, exhibited a significantly lower pH and a greater pCO₂ with no change in the [HCO₃^–] level. In vitro, the 95% N₂ + 5% CO₂ gassing (simulated hypoxia) group exhibited a slight increase in [HCO₃^–] with no change in pCO₂ or pH whereas the 50% N₂ + 50% CO₂ gassing and the 100% CO₂ gassing (simulated hypoxia and hypercapnia) groups exhibited a significant increase in [HCO₃^–] under high pCO₂-induced acidification. Conclusions: Under anoxia and CO₂ retention during aortic cross-clamping, the BCP solution can be a bicarbonate donor to the myocardium.