Epicardial measurement of alterations in extracellular pH and electrolytes during ischemia and reperfusion in cardiac surgery

Background: Simultaneous measurements of extracellular pH, potassium (K⁺), and calcium (Ca²⁺) activity may be indicative of myocardium vitality or ischemia.

Method: Ten consecutive patients undergoing elective coronary artery bypass grafting (CABG) were studied according Ethics committee permission and informed consent. Epicardial extracellular pH, potassium, and calcium were measured by miniaturized disposable multi-sensor probe. Blood gases and electrolytes were derived with measurements of arterial and mixed venous blood samples at intervals during surgery.

Results: Before ischemia, epicardial pH was moderately (P<0.05), and K⁺, and Ca²⁺ were closely correlated (P<0.001) with blood values. During reperfusion, epicardial measurements were weakly correlated (P<0.001) with blood values for pH and venous K⁺, and Ca²⁺. It was moderately correlated with arterial K⁺ and Ca²⁺. The mean epicardial baseline levels for pH in all patients were 8.04±0.22 AU for the right ventricle (RV) and 8.03±0.21 AU for the left ventricle (LV); for Ca²⁺ 0.23±0.07mmol/l (RV) and 0.20±0.10mmol/l; and for K⁺ 4.54±1.51mmol/l (RV) and 4.38±0.57mmol/l (LV).

Conclusion: The measurements indicated intraoperative episodes of ischemia and reperfusion with reproducible trends of extracellular pH, K⁺, and Ca²⁺, which results in electrolyte patterns applicable for detecting inadequate myocardial protection during cardiac surgery in patients.