Oxygenation of cardioplegic solutions: a note of caution

The merits of oxygenated crystalloid cardioplegic solutions have been well established in experimental animals. The positive effects of oxygenation of Plasmalyte B (Sabax Ltd) and St. Thomas Hospital solution (Plegisol) were achieved by gassing with 95% O2/5% CO2 and 100% O2, respectively. In view of the marked pH differences induced by these gas mixtures, we evaluated the effect of mode of oxygenation on myocardial recovery during reperfusion after hypothermic cardioplegic arrest. Oxygenation with 100% O2 of Plasmalyte B containing high K+ levels caused marked deterioration in myocardial recovery, whereas the mode of oxygenation did not affect recovery after arrest with St. Thomas Hospital solution. Because the major differences between these solutions reside in their respective K+, Mg2+, and HCO3- contents, the effects of variations in the levels of these ions were investigated. The results showed that oxygenation with 100% O2 was deleterious only in the presence of high K+ (29 mmol/L), low Mg2+ (3 mmol/L), and high NaHCO3 (28 mmol/L) levels. The marked decline in mechanical recovery during reperfusion was associated with significant changes in myocardial adenosine triphosphate and intracellular Ca2+ levels. Although an explanation for these findings is not readily available, it is suggested that complex ionic interactions and possibly oxygen free radical generation may lead to intracellular Ca2+ overload, depression in mitochondrial adenosine triphosphate generation, and, hence, deterioration in mechanical recovery.