Does Normothermia Afford Better Conditions for Myocardial Oxygenation than Hypothermia During Artificial Coronary Perfusion?:A Clinical Study of Aortic Valve Replacement Patients

Myocardial oxygenation and lactate metabolism, changes in haemoglobin oxygen affinity and postoperative myocardial recovery were studied during normothermic (NCP) and hypothermic (HCP) coronary perfusion in association with aortic valve replacements. The P50 values were maintained at prebypass levels in the NCP-group, but were significantly lower in the HCP-group than in the NCP-group during and after bypass. This was reflected in a greater oxygen extraction from the haemoglobin by the myocardium only after bypass. During coronary perfusion, the arterial-coronary sinus oxygen content difference decreased by about 70% and the coronary sinus blood PO2 and oxygen saturation increased by about 60% and 80%, respectively. During rewarming after hypothermia in the HCP-group there was a marked lactate production by the myocardium in 3 out of 8 patients. After bypass the myocardial oxygen extraction was only slightly diminished as compared to the preoperative control in both groups. At this stage ne signs of defective oxygenation caused by low P50 values were detected in the patients of the HCP-group. There was a greater degree of deterioration in the mechanical cardiac performance in the NCP-group than in the HCP-group postoperatively, as assessed by CI-PCWP and LVSWI-PCWP relationships. The CK levels were postoperatively higher in the NCP-group than in the HCP-group. There was a great number of clinical findings suggestive of myocardial injury in the NCP-group, but not in the HCP-group. The conclusion reached is that the patients studied were able to compensate for the increased oxygen affinity found during and after the hypothermic coronary perfusion, that the coronary perfusion system used per se causes abnormality in the myocardial oxygen utilization in relation to the blood flow and that normothermic coronary perfusion is associated with a greater amount of myocardial injury than hypothermic coronary perfusion under the conditions studied.