NEAR-INFRARED MONITORING OF MYOCARDIAL OXYGENATION DURING INTERMITTENT WARM BLOOD CARDIOPLEGIA

Objective: This study was performed to examine the ability of near-inf rared spectroscopy to monitor tissue oxygenation in the cardioplegical ly arrested heart and to assess myocardial oxygen metabolism during in termittent warm blood cardioplegia. Methods: Using a three-wavelength near-infrared spectroscopy, we continuously measured myocardial tissue oxygen saturation and the tissue hemoglobin concentration during inte rmittent warm blood cardioplegia. Under normothermic cardiopulmonary b ypass, 20 dogs received three 5-min periods of antegrade warm blood ca rdioplegia, interrupted by three 10-min episodes of ischemia in group 1 (n = 7), three 15-min episodes of ischemia in group 2 (n = 6), or th ree 20-min episodes of ischemia in group 3 (n = 7). Results: Myocardia l oxygen saturation during beating and ventricular fibrillation was 80 +/- 1 and 59 +/- 1%, respectively. Myocardial oxygen saturation rapid ly increased to 82 +/- 1% at blood cardioplegic infusion and decreased to is F 1% 3 min after cardioplegic interruption. The time required t o reach the peak oxygen saturation level decreased significantly at th e second and third infusions compared to the first infusion in group 1 , whereas the time increased significantly at the third infusion in gr oups 2 and 3. The slower rate of increase in oxygen saturation suggest ed reduced coronary vasodilator reserve due to microvascular abnormali ties. Reperfusion ventricular fibrillation occurred in none of group 1 , one of group 2 and three of group 3. Conclusions: Near-infrared spec troscopy is a useful method of continuously monitoring myocardial oxyg enation and ischemia during warm heart surgery. Episodes of isthemia l onger than 10 min during warm blood cardioplegia resulted in less-than -optimal myocardial preservation and should be avoided. (C) 1997 Elsev ier Science B.V.