COOLING GRADIENTS AND FORMATION OF GASEOUS MICROEMBOLI WITH CARDIOPULMONARY BYPASS - AN ECHOCARDIOGRAPHIC STUDY

Background. Previous studies demonstrated gas emboli formation during rewarming from hypothermia on cardiopulmonary bypass when the temperat ure gradient exceeded a critical threshold. It also has been suggested that formation of arterial gas emboli may occur during cooling on car diopulmonary bypass when cooled oxygenated blood exiting the heat exch anger is warmed on mixture with the patient's blood. The purpose of th is study was to determine under what circumstances gas emboli formatio n would occur during cooling on cardiopulmonary bypass. Methods. Eight anesthetized mongrel dogs were placed on cardiopulmonary bypass using a roller pump, membrane oxygenator, and arterial line filter. For emb oli detection, we positioned a transesophageal echocardiographic probe at the aortic arch distal to the aortic cannula and Doppler probes at the common carotid artery and the arterial line. Cooling gradients be tween normothermic blood and cooled arterial perfusate of 5 degrees, 1 0 degrees, 15 degrees, 20 degrees, and 0 degrees C (isothermal control s) were investigated. In addition to preestablished temperature gradie nts, we investigated the effect of rapid cooling (maximal flow through the heat exchanger at a water bath temperature of 4 degrees C) after the initiation of normothermic cardiopulmonary bypass. Results. Minima l gas emboli were detected at the aortic arch at gradients of 10 degre es C or greater. The incidence of emboli was related directly to the m agnitude of the temperature gradient (p < 0.01). No emboli were detect ed at the carotid artery. During rapid cooling, no emboli were observe d either at the aorta or at the carotid artery. Conclusions. Cooling g radients of 10 degrees C or greater may be associated with gas emboli formation, but they may be of limited clinical significance because no emboli were detected distal to the aortic arch. During the applicatio n of rapid cooling, no emboli formation was observed. (C) 1997 by The Society of Thoracic Surgeons.