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徐忠憲,金炯默 고려대학교 의과대학 1991 고려대 의대 잡지 Vol.28 No.1
It is widely recognized that adequate preservation of the ischemic myocardium is of primary importance in cardiac operations. Yet, there are no techniques available for intraoperative assessment of the adequacy of myocardial preservation during the period of aortic cross-clamp. With the use of cold cardioplegia, continuous intraoperative measurement of myocardial temperature has been found useful in monitoring the adequacy of the delivery of the cardioplegic solution to the ischemic myocardium. It is, however, more important to monitor the metabolic status of the ischemic tissues, since tissue acidosis can progress even in the presence of adequate myocardial hypothermia. The continuous measurement of intramyocardial pH was used to follow the progression of ischemia, and it was correlated to the recovery of left ventricular function following hypothermic global ischemia. New miniature intramyocardial probes with dual pH- and temperature-sensing capability were placed into the left ventricular free walls of 12 mongrel dogs undergoing ischemic arrest during tardiopulmonary bypass. All dogs underwent a single period of aortic cross-clamping for 90 minutes. Systemic moderate hypothermia (around 25℃ esophageally) was employed in all dogs. In six of them, modified St. Thomas hospital cardioplegic solutions at 4℃ was infused every 30 minutes during aortic cross-clamping and cold saline was also used for local myocardial cooling(Group Ⅰ). In other six dogs, only cold saline was used for myocardial protection without intermittent infusion of cardioplegic solution(Group Ⅱ). Intramyocardial pH and temperature were continuously monitored during cardiopulmonary bypass with PH & Thermo Monitor(Chemical Ins. Co. Model PT-501). To assess the degree of myocardial injury, CK-MB isoenzyme was measured before cardiopulmonary bypass(pre-CPB), and at 20 minutes(post-20), 40 minutes(post-40), and 60 minutes (post-60) after cardiopulmonary bypass. Postoperative recovery of left ventricular function was also evaluated by measuring cardiac output and dp/dt max. at the same times. Baseline intrarmyocardial pH before CPB averaged 7.49±0.12. Intramyocardial pH decreased following aortic cross-clamping. Decrease in intrarnyocardial pH was less in Group Ⅰ than in Group Ⅱ. The lowest intramyocardial pH during ischemia in Group Ⅰ ranged between 6.55 and 6.81, but those in Group Ⅱ ranged between 5.90 and 6.25. Mean lowest intramyocardial pH in both groups were significantly different, 6.70±0.09 in Group Ⅰ and 6.06± 0.14 in Group Ⅱ (p<0.01). As compared with baseline values, CK-MB isoenzymes at 60 minutes after CPB increased about 3.2 folds in Group Ⅰ and more significantly increased in Group Ⅱ by 14 folds(p<0.05). In Group Ⅰ, cardiac output and dp/dt max. at 60 minutes after CPB was recovered in average to 93.8±4.2% and 95.5±3.0% of baseline value, respectively. But in Group Ⅱ, postischemic myocardial recovery was significantly low as 65.8±7.3% and 61.8±7.5%, respectively(p<0.01). In conclusion, Group Ⅰ which employed cardioplegic solution and local iced saline cooling for myocardial protection demonstrated less decreased intramyocardial pH during ischemia and better postoperative recovery of myocardial function than Group Ⅱ. However, Group Ⅱ which employed only iced saline for myocardial protection demonstrated further decrease in myocardial pH during ischemia and poorer postoperative recovery of myocardial function than Group Ⅰ. These data indicate that continuous intraoperative measurement of intramyocardial pH is a practical and useful method for assessment of the adequacy of myocardial preservation during ischemia with aortic cross-clamp, and it may be valuable for further clinical use.