Changes in cerebral hemodynamics and oxygenation during hypothermic cardiopulmonary bypass in neonates and infants

Delay in development after open-heart surgery in infants has frequently been reported. Inadequate brain perfusion and oxygenation during deep hypothermic cardiopulmonary bypass (CPB) may play an important role. We investigated the effect of CPB on cerebral perfusion and oxygenation in 12 neonates and infants (age 0-11 months) undergoing open-heart surgery. Changes in cerebral blood volume (ΔCBV; in ml/100 g brain tissue) and oxidation level of the intracerebral mitochondrial enzyme cytochrome aa₃ (ΔCytaa₃; in μmol/l) were measured with near infrared spectroscopy. Nasopharyngeal temperature (T_nas) for assessment of changes in brain temperature, and mean arterial blood pressure (MAP) were monitored continuously. CBV lowered during cooling and increased during rewarming. These changes were only related with changes in Tnas (p < 0.001; 0.07 ml·100 g^-1/°C). No relation was found with changes in MAP or pump flow rate of the heart-lung machine. During steady-state hypothermic CPB, changes in CBV were only related to changes in MAP (p < 0.001). The individual regression lines between ΔCBV and MAP became steeper at lower absolute T_nas. Cytaa₃ showed an increase shortly after the initiation of CPB in 9 patients, with a sustained decrease to baseline values in 8 patients towards the end of the CPB period. Two patients who had a circulatory arrest during CPB had a sharp decrease in Δcytaa₃ after cessation of the heart-lung pump and showed no complete recovery of ΔCytaa₃ to baseline at the end of the CPB period. We conclude that changes in CBV during CPB are related to changes in T_nas. During deep hypothermic steady-state CPB, changes in CBV and MAP were related to each other, suggesting lack of cerebral autoregulation. The large decrease in Cytaa₃ in 2 patients with circulatory arrest suggests that this procedure compromises energy metabolism of the brain cell.