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Ischemic threshold during cold blood cardioplegic arrest: monitoring with tissue pH and pO2
M Carrier1, S Trudelle, P Thai
1Cardiovascular Division, Montreal Heart Institute, QC, Canada.
Background:
Several studies have suggested that measuring interstitial pH and pO2, may be useful to monitor ischemia throughout cardioplegic arrest during cardiac surgery.
Methods:
To evaluate the levels of myocardial tissue pH and pO2 that correlate with significant ischemia, 7 dogs underwent cold blood cardioplegic arrest and subsequent incremental episodes of 5, 10, 20 and 40 min of ischemia interrupted by cardioplegic infusion over 10-min periods.
Results:
Myocardial tissue pH and pO2 were monitored with probes implanted in the anterior and lateral walls of the left ventricle. The release of CK, troponine T and lactate was measured before and after each episode of ischemic arrest. Tissue 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 pO2 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 arrest. CK, troponine T and lactate serum levels increased significantly only following 40 min of ischemic arrest. Myocardial temperature decreased to an average minimum of 14+/-1 degrees C during cardioplegic infusion.
Conclusions:
A myocardial tissue pH lower than 7.04 (90% CI, upper limit of 6.82+/-0.14) and a tissue pO2 lower than 22 mmHg (90% CI, upper limit of 14+/-5 mmHg) correlate with anaerobic metabolism and myocardial ischemia during cold cardioplegic arrest.