Factors influencing the change in cerebral hemodynamics in pediatric patients during and after corrective cardiac surgery of congenital heart diseases by means of full-flow cardiopulmonary bypass

Background: The pathophysiology of hypoxic-ischemic brain injury in relation to extracorporeal circulation is multifactorial and can be interpreted, in part, as possible alteration in cerebral perfusion and inadequate oxygen delivery to the brain cells. The aim of this study was to evaluate influencing factors on the change in cerebral blood flow velocity (CBFV) patterns determined by transcranial Doppler sonography (TCD) in infants who undergo corrective cardiac surgery by means of full-flow cardiopulmonary bypass (CPB). Methods: Included in the study were 67 neonates, infants, and children with a median age of 4 months (0.1-70 months), median weight of 4.8 kg (2.5-18.8 kg), and with cyanotic and noncyanotic congenital heart disease (CHD), who underwent surgical correction of CHD by means of CPB [flow rate 144±47 ml/kg body weight (BW)] and the alpha-stat strategy. The patients were divided into three groups with respect to the minimum rectal temperature during perfusion: deep hypothermic CPB (<18°C) n=18, moderate hypothermic CPB (22-35°C) n=29, normothermic CPB (36°C) n=20. Continuous determination of mean flow velocity (V_mean) in the middle cerebral artery (MCA) by TCD provided qualitative on-line information on cerebral perfusion. The pulsatility index (PI) was calculated in accordance with the formula: PI = Maximum flow velocity - end - diastolic flow velocity/Mean flow velocity and was used as a parameter for the qualitative assessment of cerebrovascular resistance after the end of CPB. Results: The V_mean was significantly increased 15 min after cross-clamping in the normothermic group (p=0.03) and decreased in the moderate hypothermic group (p=0.02) and deep hypothermic group (p=0.009). The postoperative V_mean values correlated significantly with age (r=0.79, p<0.0001), weight (r=0.75, p<0.0001), bypass time (r=-0.51, p=0.0006), and minimum rectal temperature (r=0.60, p=0.0001). Mean arterial pressure and hemoglobin concentration, but not pCO₂, seem to significantly influence the change in V_mean after the termination of CPB (r=0.5, p=0.001; r=-0.55, p=0.002, respectively). In comparison with the values at the start of CPB, the V_mean was significantly decreased after the end of CPB in the hypothermic and moderate hypothermic groups and still significantly elevated in the normothermic group. The age-independent PI was increased after termination of bypass in all groups (p<0.05) and still slightly elevated after the end of operation in the hypothermic group (p=0.05). Conclusions: The changes in CBFV patterns before, during, and after the termination of CPB were dependent on age, weight, perfusion pressure, and degree of hypothermia during CPB.