POLYETHYLENE GLYCOL-CONJUGATED SUPEROXIDE-DISMUTASE IMPROVES RECOVERYOF POSTISCHEMIC HYPERCAPNIC CEREBRAL BLOOD-FLOW IN PIGLETS

We tested the hypothesis that administering polyethylene glycol-conjug ated superoxide dismutase (PEG-SOD) either before global cerebral isch emia or at the time of reperfusion would alter recovery of cerebral bl ood flow (CBF; microspheres) response to alteration in arterial PCO2 i n pentobarbital-anesthetized, mechanically ventilated piglets (1 to 2- wk old). CBF was measured at an arterial PCO2 of approximately 3.3, 5. 3, and 8.7 kPa before and 2 h after ischemia (10 min aortic cross clam p). To determine the effect of preischemic versus postischemic treatme nt with PEG-SOD, each piglet received two i.v. drug injections of eith er 30 000 U PEG-SOD or an equal volume of PEG diluent in a randomized, blinded fashion before ischemia and just before reperfusion. Cerebral oxygen consumption and somatosensory evoked potentials were measured during reperfusion as an assessment of brain function. During reperfus ion, no group demonstrated delayed hypoperfusion. Hypercapnic CBF was less during reperfusion (48 t 6 mL/min/100 g)compared with preischemia (69 +/- 10 mL/min/100 g) in PEG/PEG-treated piglets. However, hyperca pnic CBF during reperfusion was not different from preischemic values with either preischemic or postischemic PEG-SOD treatment. Improved re turn of hypercapnic CBF in PEG-SOD-treated piglets was not attributabl e to improved postischemic cerebral oxygen consumption. Somatosensory evoked potential amplitude was decreased similarly during reperfusion (approximately 25% of preischemic values) in all groups. We conclude t hat PEG-SOD alters CBF response to hypercapnia after transient global cerebral ischemia in piglets via a mechanism that is not related to al tered oxygen consumption or electrical activity.