Tissue oxygen tension during regional low-flow perfusion in neonates

Objective: We examined cerebral cortical and peripheral organ tissue Po-2 values in a neonatal piglet model of regional low-flow perfusion. Methods: Twenty-one neonatal piglets were placed on cardiopulmonary bypass, were cooled to 18degreesC, then underwent either deep hypothermic circulatory arrest or regional low-flow perfusion at 20 or 40 mL/(kg X min) for 90 minutes. Regional low-flow perfusion was carried out by advancing the aortic cannula into the proximal innominate artery. Tissue mean Po-2 and Po-2 distribution were measured in the cerebral cortex, liver, small bowel, and skeletal muscle throuch the principle of oxygen-dependent quenching of phosphorescence. Measured quantities were compared by analysis of variance or the Fisher exact test. Results: During regional low-flow perfusion, axillary and femoral arterial pressures, respectively, were 55 +/-15 and 8 +/- 4 num Hg at 40 mL/(kg X min) and 37 +/- 10 min Hg (P =.04) and 17 +/- 5 turn Hg (P =.08) at 20 mL/(kg X min). Venous saturations were 95% +/- 6% at 40 mL/(kg X min) and 84% +/- 6% at 20 mL/(kg X min) (P =.03 at 15, 30, and 45 minutes). Cortical PO2 was similar to prebypass values during regional low-flow perfusion at 40 mL/(kg X min) (53 +/- 5 turn Hg) but declined during reperfusion and recovery. Cortical Po-2 was lower than before bypass during low-flow perfusion at 20 mL/(kg X min) (38 7 num Hg) but increased during reperfusion. Po-2 in liver and bowel was less than 10 mm Hg during low-flow perfusion at both 20 and 40 mL/(kg X min). Fraction of oxygen distribution with Po,, lower than 15 mm Hg was less during perfusion at 40 mL/(kg X min) than at 20 mL/(kg X min) (P = .001). Three of 6 piglets that received a 40-mL/(kg X min) flow rate had significant upper torso edema, metabolic acidosis, and an unstable recovery period, whereas zero of 6 piglets that received a 20-mL/(kg X min) flow rate did. Conclusions: In a piglet model, regional low-flow perfusion at 20 mL/(kg X min) resulted in lower cortical tissue oxygenation but better recovery than did perfusion at 40 mL/(kg X min). Neither flow rate adequately oxygenated organs in the lower torso.