Cerebrovascular response to carbon dioxide in lambs receiving extracorporeal membrane oxygenation.

OBJECTIVE

To determine if the institution of extracorporeal membrane oxygenation (ECMO) alters the cerebrovascular response to changes in PaCO2.

DESIGN

Prospective, randomized, controlled animal trial.

SUBJECTS

Anesthetized 1- to 7-day-old lambs of mixed breed (n = 16).

SETTING

University research laboratory.

INTERVENTIONS

The experimental group was placed on ECMO. Both experimental and control groups (n = 8) were exposed to three concentrations of PaCO2 (hypocarbia, normocarbia, and hypercarbia) by varying mechanical ventilation and by adding carbon dioxide to the ventilator gases.

MEASUREMENTS AND MAIN RESULTS

Cerebral blood flow was measured by the radiolabeled microsphere method. Arterial blood gases and sagittal sinus blood gases were drawn at the time of cerebral blood flow measurement so that cerebral metabolism, cerebral oxygen transport, and extraction could be calculated. In the control group, as PaCO2 increased from 34 +/- 2 (SD) to 53 +/- 4 torr (4.5 +/- 0.3 to 7.1 +/- 0.5 kPa), cerebral blood flow increased from 53 +/- 12 to 147 +/- 50 mL/min/100 g. This increase in cerebral blood flow was not different from that of the ECMO group, where PaCO2 increased from 33 +/- 2 to 56 +/- 3 torr (4.4 +/- 0.3 to 7.5 +/- 0.4 kPa) and cerebral blood flow increased from 48 +/- 17 to 106 +/- 38 mL/min/100 g. As PaCO2 decreased from 34 +/- 2 to 19 +/- 2 torr (4.5 +/- 0.27 to 2.5 +/- 0.27 kPa), cerebral blood flow decreased from 53 +/- 12 to 43 +/- 8 mL/min/100 g in the control group. This decrease was not different from that of the ECMO group, where cerebral blood flow decreased from 48 +/- 17 to 39 +/- 10 mL/min/100 g as PaCO2 decreased from 33 +/- 2 to 22 +/- 3 torr (4.4 +/- 0.3 to 2.9 +/- 0.4 kPa). When regional cerebral blood flow was analyzed, no regional differences in the cerebrovascular responses to PaCO2 between ECMO and control groups were found. The cerebral metabolic rate was not different between ECMO and control groups at any level of PaCO2, nor was the cerebral metabolic rate affected by changes in PaCO2. Oxygen extraction increased with hypocarbia and decreased with hypercarbia in a similar fashion in both ECMO and control groups.

CONCLUSION

The cerebrovascular response to changes in PaCO2 was unaffected by ECMO.