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

Simultaneous measurements of extracellular pH, potassium (K(+)), and calcium (Ca(2+)) activity might be indicative of myocardium vitality or ischemia. Ten consecutive patients undergoing elective coronary artery bypass grafting were studied. Epicardial extracellular pH, potassium, and calcium were measured by a miniaturized disposable multi-sensor probe. Blood gases and electrolytes were derived with measurements of arterial and mixed venous blood samples at intervals during surgery. The mean epicardial baseline levels for pH in all patients were 8.04+/-0.22 arbitrary units (AU) for the right ventricle (RV) and 8.03+/-0.21 AU for the left ventricle (LV); for Ca(2+) 0.23+/-0.07 mmol/l (RV) and 0.20+/-0.10 mmol/l (LV); and for K(+) 4.54+/-1.51 mmol/l (RV) and 4.38+/-0.57 mmol/l (LV). Before ischemia, epicardial pH was moderately (p<0.05), and K(+), and Ca(2+) were closely correlated (p<0.001) with blood values. During reperfusion, epicardial measurements were weakly correlated (p<0.001) with blood values for pH, venous K(+) and Ca(2+), but moderately correlated with arterial K(+) and Ca(2+) (p<0.01). The measurements indicated intraoperative episodes of ischemia and reperfusion with reproducible trends of extracellular pH, K(+), and Ca(2+), which results in electrolyte patterns applicable for detecting inadequate myocardial protection during cardiac surgery in patients.