Microembolism during cardiopulmonary bypass: a comparison of bubble oxygenator with arterial line filter and membrane oxygenator alone

Abstract

Microemboli can be detected in the cerebral circulation during cardiopulmonary bypass with transcranial Doppler. They are likely to be responsible for the microvascular occlusions that have been seen in the retina and they may contribute to neuropsychological damage that has been demonstrated after cardiac surgery. Twenty patients undergoing routine coronary artery bypass graft surgery were allocated to either a Harvey 1700 bubble oxygenatorwith a Pall 40μ arterial line filter or a Harvey 4000 membrane oxygenator with no arterial line filter. All cases received pulsatile flow perfusion with core cooling to 28°C. A standard surgical technique was used with distal anastomoses performed during cold cardioplegic arrest and proximal anastomoses performed with coronary perfusion during systemic rewarming. Microembolic events were measured by the counting of flow disturbances over the pattern of pulsatile flow as detected by Doppler. Median bypass time was 69 minutes (range 45-95) for the bubbler group and 79 minutes (range 50-115) for the membrane group. The microembolic event count was normalized to the number of events per 15 minute period of bypass. The median number of microembolic events per 15 minute period of bypass was 28 (range 6-54) for the bubble group and 21 (range 10-65) for the membrane group. There were no significant differences between the lengths of bypass between the two groups (Mann-Whitney p = 0.202) or the number of microemboli recorded per 15 minute period of bypass (Mann-Whitney p = 0.224). We conclude that the previously demonstrated excess generation of gaseous microemboli from bubble oxygenators over membrane oxygenators is negated by the use of a 40μ arterial line filter with the bubble oxygenator.