Assessment of myocardial protection during global ischemia with myocardial gas tension monitoring.

Intramyocardial gas tension monitoring with mass spectrometry allows for the continuous assessment of myocardial metabolic activity during prolonged global ischemia. With aortic cross-clamping there is a rapid decrease in intramyocardial oxygen tension (PmO2) and a steady increase in carbon dioxide tension (PmCO2). In laboratory studies the extent to which myocardial metabolic activity is reduced has correlated with the degree of myocardial protection being afforded. In the present study the metabolic consequences of single-dose versus multiple-dose infusions of a hyperkalemic cardioplegic solution were compared in 23 patients undergoing aortic valve replacement (AVR) for severe aortic stenosis. Group I (n = 13) had single-dose cardioplegia during AVR, while group II (n = 10) had multiple-dose cardioplegia. The preoperative status and the surgical procedures were identical except for two multiple-dose patients who also underwent single coronary bypass grafting. In group I the PmCO2 rose steadily and at cross-clamp release was 182 +/- 20 mm Hg, while in group II the PmCO2 rose only to 77 +/- 8 mm Hg (P less than 0.01). During reperfusion the peak PmCO2 in group I was 219 +/- 22 mm Hg versus 111 +/- 5 mm Hg in group II (P less than 0.01). After operation six patients in group I required pharmacologic support, and two other patients died of low cardiac output. In contrast, only one patient in group II required inotropic support, and there were no deaths. The significantly lower PmCO2 values with multiple-dose cardioplegia suggest both reduced metabolic activity and washout of metabolic end products, with resultant improved myocardial protection, evidenced by less postoperative left ventricular dysfunction.