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PEDIATRIC ANESTHESIA

The Effect of Hematocrit on Cerebral Blood Flow Velocity in Neonates and Infants Undergoing Deep Hypothermic Cardiopulmonary Bypass

Eva M. Gruber, MD^*, Richard A. Jonas, MD, Jane W. Newburger, MD, David Zurakowski, PhD, Dolly D. Hansen, MD^*, and Peter C. Laussen, MB, BS^*

Departments of *Anesthesiology, Surgery, and Pediatrics, Harvard Medical School; and Departments of *Anesthesia, Cardiovascular Surgery, Cardiology, and Research Computing & Biostatistics, Children’s Hospital, Boston, Massachusetts

Address correspondence and reprint requests to Peter C. Laussen, MB, BS, Department of Anesthesia, Cardiac Anesthesia Service, Children’s Hospital, 300 Longwood Ave., Boston, MA 02115. Address e-mail to laussen{at}a1.tch.harvard.edu

Varying degrees of hemodilution are used during deep hypothermic cardiopulmonary bypass. However, the optimal hematocrit (Hct) level to ensure adequate oxygen delivery without impairing microcirculatory flow is not known. In this prospective, randomized study, cerebral blood flow velocity in the middle cerebral artery was measured using transcranial Doppler sonography in 35 neonates and infants undergoing surgery with deep hypothermic cardiopulmonary bypass. Patients were randomized to low Hct (aiming for 20%) or high Hct (aiming for 30%) during cooling on cardiopulmonary bypass (CPB). Systolic (V_s), mean (V_m), and diastolic (V_d) cerebral blood flow velocity, as well as pulsatility index (PI = [V_s - V_d]/V_m) and resistance index (RI = [V_s - V_d]/V_s) were recorded at six time points: postinduction, at cannulation, after 10 min cooling on CPB, rewarmed to 35°C on CPB, immediately off CPB, and at skin closure. V_m was significantly lower in the high Hct group compared with that in the low Hct group during cooling (P < 0.01). Postinduction, the high Hct group demonstrated significantly lower V_d immediately off CPB (P < 0.01) and significantly lower V_m and V_s at skin closure (P < 0.001). We conclude that there is an inverse relation between hematocrit and cerebral blood flow velocity during deep hypothermic cardiopulmonary bypass in neonates and infants.

Implications: There is an inverse relation between hematocrit and cerebral blood flow velocity during deep hypothermic cardiopulmonary bypass in neonates and infants. Further studies correlating Hct and cerebral blood flow velocity with cerebral metabolic rate and neurologic outcome are necessary to determine the optimal Hct during deep hypothermic cardiopulmonary bypass.

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