EFFECT OF AORTIC CANNULA CHARACTERISTICS AND BLOOD VELOCITY ON TRANSCRANIAL DOPPLER-DETECTED MICROEMBOLI DURING CARDIOPULMONARY BYPASS

Objectives: Cerebral microemboli are responsible to a large extent for the neuropsychiatric deficits after cardiac surgery. Differences in c annula size during cardiopulmonary bypass (CPB) will result in differe nt velocities of blood exiting the aortic cannula. This study determin ed whether the number of transcranial Doppler (TCD)-detected emboli in the middle cerebral artery (MCA) during CPB correlated with blood spe ed or the direction of flow as determined by the shape of the aortic c annula. Design: Patients were studied prospectively for evidence of TC D-detected emboli. If patients met the inclusion criteria, the choice of cannula was determined by surgical preference. Setting: All studies were conducted at a single tertiary care academic cardiac surgery hos pital by a single observer. Participants: Thirty-two patients undergoi ng first-time elective aortocoronary bypass surgery who were free of n eurologic dysfunction or peripheral vascular disease and weighed 60 to 85 kg were studied. Patients who had other concurrent cardiac operati ons or who were in cardiogenic shock were excluded. Interventions: Thr ee aortic cannula types for elective aortocoronary bypass surgery were used: 24F curved (n = 19), 24F straight (n = 6), and 22F straight (n = 7), with internal diameters (IDs) of 7.2, 6.6, and 5.9 mm, respectiv ely. TCD-detected emboli were identified in the MCA. Measurements and Main Results: The rate of TCD-detected emboli (0.02 to 11.4 emboli per minute) was not related to the velocity of blood (46 to 77 cm/s) and was not affected by the choice of either a straight or curved aortic c annula.Conclusions: The choice of a straight or curved aortic cannula or of a 24F versus 22F cannula may not be important with respect to th e number of cerebral microemboli. Copyright (C) 1998 by W.B. Saunders Company.