Cerebral microemboli during cardiopulmonary bypass: Increased emboli during perfusionist interventions

Background. Microemboli to the cerebral circulation occur during cardiopulm onary bypass (CPB) and can contribute to postoperative neurologic dysfuncti on. Cerebral microemboli are known to occur during specific surgical interv entions, but the source of a large proportion of emboli remains unexplained . We investigated whether interventions by the perfusionist could account f or the appearance of cerebral microemboli. Methods. Transcranial Doppler ultrasonography was used to continuously moni tor the middle cerebral artery of 18 patients undergoing coronary artery by pass grafting. The CPB circuit consisted of a softshell venous reservoir, a hollow-fiber membrane oxygenator, and a 32-mu m arterial filter. The mean embolic rate was calculated for three time periods: (1) during surgical int erventions (aortic cannulation and decannulation, cross-clamp application a nd removal, CPB start and end, and start of cardiac ejection); (2) during p erfusionist interventions (blood sampling and drug administration into the venous reservoir); and (3) during baseline (all other time periods during C PB). Results. Microemboli were detected in all patients (mean +/- standard devia tion, 207 +/- 142 per patient, median, 132). The number of emboli per minut e was significantly (p < 0.001) higher during perfusionist interventions (6 .9 +/- 4.5) than during surgical interventions (1.5 +/- 1.5) or during base line (0.4 +/- 0.5). Drug administration resulted in a higher embolic rate t han blood sampling. Conclusions. Interventions by the perfusionist account for a large proporti on of previously unexplained cerebral microemboli during CPB. These emboli likely represent air bubbles that are not eliminated by the arterial line f ilter. Although further studies of additional types of CPB circuits are req uired, we believe that air in the venous reservoir should be avoided whenev er possible to minimize the risk of neurologic injury. (C) 1999 by The Soci ety of Thoracic Surgeons.