Milrinone increases middle cerebral artery blood flow velocity after cardiopulmonary bypass.

OBJECTIVE

To evaluate the effects of milrinone on middle cerebral artery blood flow velocity (Vmca) and pulsatility index (PI) during normocapnia and hyperventilation in adults after cardiopulmonary bypass (CPB).

DESIGN

A prospective study.

SETTING

University-affiliated hospital and Veterans Affairs Medical Center.

PARTICIPANTS

Twenty-five adults with left ventricular ejection fraction >40% undergoing coronary artery bypass graft surgery.

INTERVENTIONS: After separation from CPB, using transcranial Doppler ultrasonography, peak and mean Vmca and PI were recorded before and after the administration of 50 microg/kg of milrinone under normocapnia and with hyperventilation.

MEASUREMENTS AND MAIN

RESULTS

Heart rate, arterial blood pressure, central venous pressure, and cardiac output were documented after each study period. Compared with baseline, milrinone increased peak Vmca by 20%, increased mean Vmca by 19%, and decreased PI by 16% (p < 0.001). Before the administration of milrinone, hyperventilation decreased peak Vmca by 20%, decreased mean Vmca by 26%, and increased PI by 24% (p < 0.01). After milrinone administration, hyperventilation also decreased peak Vmca by 22%, decreased mean Vmca by 21%, and increased PI by 19% (p < 0.01). Milrinone increased cardiac index and decreased mean arterial pressure and systemic vascular resistance (p < 0.05); however, heart rate and central venous pressure remained unchanged.

CONCLUSIONS

The administration of milrinone increases cerebral blood flow after CPB most likely as a result of cerebral vasodilation. The response to hyperventilation seems to be partially preserved.