ISCHEMIC THRESHOLD DURING COLD BLOOD CARDIOPLEGIC ARREST - MONITORINGWITH TISSUE PH AND PO(2)

Background Several studies have suggested that measuring interstitial pH and pO(2), may be useful to monitor ischemia throughout cardioplegi c arrest during cardiac surgery. Methods. To evaluate the levels of my ocardial tissue pH and pO(2) that correlate with significant ischemia, 7 dogs underwent cold blood cardioplegic arrest and subsequent increm ental episodes of 5, 10, 20 and 40 min of ischemia interrupted by card ioplegic infusion over 10-min periods. Results. Myocardial tissue pH a nd pO(2) were monitored with probes implanted in the anterior and late ral walls of the left ventricle. The release of CK, troponine T and la ctate was measured before and after each episode of ischemic arrest. T issue pH decreased from 7.08+/-0.15 to 7.03+/-0.15 (p>0.05), 7.21+/-0. 15 to 7.07+0.11 (p>0.05), 7.17+/-0.15 to 6.82+/-0.14 (p<0.05) and 7.0/-0.18 to 6.63+/-0.08 (p<0.05) after 5, 10, 20 and 40 min of ischemic arrest. Tissue pO(2) decreased from 74+/-10 to 38+/-11 mmHg (p<0.05), 83+-16 to 18+/-4 mmHg (p<0.05), 9+/-22 to 14+/-5 mmHg (p<0.05) and 64/-24 to 16+/-10 mmHg (p<0.05) after 5, 10, 20 and 40 min of ischemic a rrest. CK, troponine T and lactate serum levels increased significantl y only following 40 min of ischemic arrest. Myocardial temperature dec reased to an average minimum of 14+/-1 degrees C during cardioplegic i nfusion. Conclusions. A myocardial tissue pH lower than 7.04 (90% CI, upper limit of 6.82+/-0.14) and a tissue pO(2) lower than 22 mmHg (90% CI, upper Limit of 14+/-5 mmHg) correlate with anaerobic metabolism a nd myocardial ischemia during cold cardioplegic arrest.