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 cannula size during cardiopulmonary bypass (CPB) will result in different velocities of blood exiting the aortic cannula. This study determined whether the number of transcranial Doppler (TCD)-detected emboli in the middle cerebral artery (MCA) during CPB correlated with blood speed or the direction of flow as determined by the shape of the aortic cannula.

DESIGN

Patients were studied prospectively for evidence of TCD-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 hospital by a single observer.

PARTICIPANTS

Thirty-two patients undergoing first-time elective aortocoronary bypass surgery who were free of neurologic dysfunction or peripheral vascular disease and weighed 60 to 85 kg were studied. Patients who had other concurrent cardiac operations or who were in cardiogenic shock were excluded.

INTERVENTIONS

Three 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, respectively. 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 cannula.

CONCLUSIONS

The choice of a straight or curved aortic cannula or of a 24F versus 22F cannula may not be important with respect to the number of cerebral microemboli.