Tissue oxygen tension during regional low-flow perfusion in neonates

Abstract

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 18 degrees C, 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 through 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 mm Hg at 40 mL/(kg x min) and 37 +/- 10 mm Hg (P =.04) and 17 +/- 5 mm 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 Po(2) was similar to prebypass values during regional low-flow perfusion at 40 mL/(kg x min) (53 +/- 5 mm 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 mm 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(2) 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.