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 P aco(2). Design: Prospective, randomized, controlled animal trial. Subj ects: Anesthetized 1- to 7-day-old lambs of mixed breed (n = 16). Sett ing: University research laboratory. Interventions: The experimental g roup was placed on ECMO. Both experimental and control groups (n = 8) were exposed to three concentrations of Paco(2) (hypocarbia, normocarb ia, and hypercarbia) by varying mechanical ventilation and by adding c arbon dioxide to the ventilator gases. Measurements and Main Results: Cerebral blood flow was measured by the radiolabeled microsphere metho d. Arterial blood gases and sagittal sinus blood gases were drawn at t he time of cerebral blood flow measurement so that cerebral metabolism , cerebral oxygen transport, and extraction could be calculated. In th e control group, as Paco(2) increased from 34 +/- 2 (SD) to 53 +/- 4 t orr (4.5 +/- 0.3 to 7.1 +/- 0.5 kPa), cerebral blood flow increased fr om 53 +/- 12 to 147 +/- 50 mL/ min/100 g. This increase in cerebral bl ood Bow was not different from that of the ECMO group, where Paco(2) i ncreased from 33 +/- 2 to 56 +/- 3 torr (4.4 +/-3 to 7.5 +/- 0.4 kPa) and cerebral blood flow increased from 48 +/- 17 to 106 +/- 38 mL/min/ 100 g. As Paco(2) 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 d ifferent from that of the ECMO group, where cerebral blood flow decrea sed from 48 +/- 17 to 39 +/- 10 mL/ min/100 g as Paco(2) decreased fro m 33 +/- 2 to 22 +/- 3 torr (4.4 +/- 0.3 to 2.9 +/- 0.4 kPa). When reg ional cerebral blood flow was analyzed, no regional differences in the cerebrovascular responses to Paco(2) between ECMO and control groups were found. The cerebral metabolic rate was not different between ECMO and control groups at any level of Paco(2), nor was the cerebral meta bolic rate affected by changes in Paco(2). Oxygen extraction increased with hypocarbia and decreased with hypercarbia in a similar fashion i n both ECMO and control groups. Conclusion: The cerebrovascular respon se to changes in Paco(2) was unaffected by ECMO.