Effect of extracorporeal membrane oxygenation on cerebral hemodynamics in newborn lambs

Neurologic injury caused by changes in cerebral blood flow is a concern in infants treated with extracorporeal membrane oxygenation (ECMO). To investigate the hypothesis that cerebral hemodynamics would be influenced by bypass flow rates, eight ketamine anesthetized lambs (age range 1 to 8 days) had measurements of cerebral hemodynamics before and after institution of venoarterial bypass.

Cerebral blood flow (whole brain and regional) were measured using the radiolabeled microsphere technique. A left carotid artery catheter (placed without sacrificing the vessel) reference sample was used for calculation of brain blood flows. Arterial and venous (sagittal sinus) oxygen contents and blood gases were measured across the cerebral circulation. Cerebral oxygen consumption, oxygen delivery, and fractional oxygen extraction were calculated. Measurements were made pre-ECMO and after placement on venoarterial ECMO at flow rates of 50 and 100 mL/kg/min. In addition, four other lambs were studied at a flow rate of 150 mL/kg/min, and seven additional animals were used to address methodologic issues with the microsphere technique in this model.

Cerebral blood flow and oxygen delivery significantly decreased, compared with control at both flow rates of 100 and 50 mL/kg/min (87.8 +/- 5.2 vs. 36.4 +/- 6.2; and 35.1 +/- 5.8 mL/100 g/min; 5.82 +/- 0.37 vs. 2.14 +/- 0.35; and 2.19 +/- 0.39 microM/100 g/min, respectively). Cerebral fractional oxygen extraction increased significantly at a flow of 50 mL/kg, and cerebral oxygen consumption decreased significantly at a flow of 100 mL/kg. At a flow rate of 150 mL/kg/min, cerebral hemodynamic variables did not differ from control measurements.

These findings demonstrate that changes in cerebral blood flow and cerebral oxygen metabolism can occur in the newborn lamb with the initiation of ECMO, and that these changes are dependent on bypass flow rate.