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Ann Thorac Surg 1991;51:777-787
© 1991 The Society of Thoracic Surgeons

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Articles

Oxygenation of cardioplegic solutions: A note of caution

Medical Research Council Centre for Molecular and Cellular Biology, Department of Medical Physiology and Biochemistry, and Department of Anaesthesiology, University of Stellenbosch Medical School, Tygerberg, Republic of South Africa

Accepted for publication January 15, 1991.

^_* Address reprint requests to Dr Lochner, Department of Medical Physiology and Biochemistry, PO Box 63, Tygerberg 7505, Republic of South Africa.

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.

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