Effect of perfusion flow rate on tissue oxygenation in newborn piglets during cardiopulmonary bypass.

BACKGROUND: Our knowledge of the best perfusion flow rate to use during cardiopulmonary bypass (CPB) in order to maintain tissue oxygenation remains incomplete. The present study examined the effects of perfusion flow rate and patent ductus arteriosus (PDA) during normothermic CPB on oxygenation in several organ tissues of newborn piglets. METHODS: The experiments were performed on 12 newborn piglets: 6 with PDA ligation (PDA-L), and 6 without PDA ligation (PDA-NL). CPB was performed through the chest at 37 degrees C. During CPB, the flow rate was changed at 15-minute intervals, ranging from 100 to 250 ml/kg/min. Tissue oxygenation was measured by quenching of phosphorescence. RESULTS: For the PDA-L group, oxygen in the brain did not change significantly with changes in flow rate. In contrast, for the PDA-NL group, oxygen was dependent upon the flow rate. Statistically significant decreases in cortical oxygen were observed with flow rates below 175 ml/kg/min. Within the myocardium, liver, and intestine, there were no significant differences in the oxygen levels between the PDA-L and PDA-NL groups. In these tissues, the oxygen decreased significantly as the flow rate decreased below 150 ml/kg/min, 125 ml/kg/min, and 175 ml/kg/min, respectively. Oxygen pressure in skeletal muscle was not dependent on either PDA ligation or flow rate. CONCLUSIONS: In newborn piglets undergoing CPB, the presence of a PDA results in reduced tissue oxygenation to the brain but not to other organs. In general, perfusion flow rates of 175 ml/kg/min or greater are required in order to maintain normal oxygenation of all organs except muscle.