Rewarming: comparison of contemporary heat-exchangers

Heat exchange methods must be efficient in order to minimize the patient's pump time. However, comparisons of heat exchangers have been rare. Therefore, the in vivo functions of the most popular, currently available heat exchangers, Sarns, Cobe, Medtronics Maxima, and an experimental model manufactured by Haemonetics were compared. Thirty-two pigs weighing between 63-74 kg were placed on cardiopulmonary bypass with right atrial and ascending aorta cannulation through a right thoracotomy. Thermocouples were placed in the pump tubing before and after the heat exchangers, in the water line before and after the heat exchangers, in the inlet and outlet line of the pump, and the esophagus, brain, bladder, rectum, liver, myocardium, and tympanic membranes of the pigs. They were cooled until the bladder temperature was reduced to 14 degrees C, and maintained at that temperature for 10 minutes. Rewarming was begun until the bladder temperature became 37 degrees C. The pump flow was maintained between 50-60 ml/kg/min with standard ventilation. Cobe, Sarns, Maxima, and Haemonetics heat exchangers were tested and their function determined by comparing the time necessary for rewarming. The Haemonetics heat exchanger required a significant shorter time than the others to rewarm the pigs to normal bladder temperature (Cobe 82.0 +/- 12.0, Sarns 80.3 +/- 15.4, Maxima 89.0 +/- 13.9 Haemonetics 68.7 +/- 13.4, p < 0.05). The principal advantage was seen at the lowest temperatures between the Haemonetics experimental heat exchanger and the other heat exchangers. No statistically significant superiority was seen at higher temperatures. The current heat exchangers are relatively comparable but improved performance is possible with available technology.