Objective: We performed this study to determine whether brief intermittent periods of low-flow cardiopulmonary bypass during deep hypothermic circulatory arrest would improve cortical metabolic status and prolong the "safe" time of deep hypothermic circulatory arrest.
Methods: After a 2-hour baseline, newborn piglets were placed on cardiopulmonary bypass and cooled to 18 degrees C. The animals were then subjected to 80 minutes of deep hypothermic circulatory arrest interrupted by 5-minute periods of low-flow cardiopulmonary bypass at either 20 mL x kg(-1) x min(-1) (LF-20) or 80 mL x kg(-1) x min(-1) (LF-80) during 20, 40, 60, and 80 minutes of deep hypothermic circulatory arrest. All animals were rewarmed, separated from cardiopulmonary bypass, and maintained for 2 hours (recovery). The oxygen pressure in the cerebral cortex was measured by the quenching of phosphorescence. The extracellular dopamine level in the striatum was determined by microdialysis. Results are means +/- SD.
Results: Prebypass oxygen pressure in the cerebral cortex was 65 +/- 7 mm Hg. During the first 20 minutes of deep hypothermic circulatory arrest, cortical oxygen pressure decreased to 1.3 +/- 0.4 mm Hg. Four successive intermittent periods of LF-20 increased cortical oxygen pressure to 6.9 +/- 1.2 mm Hg, 6.6 +/- 1.9 mm Hg, 5.3 +/- 1.6 mm Hg, and 3.1 +/- 1.2 mm Hg. During the intermittent periods of LF-80, cortical oxygen pressure increased to 21.1 +/- 5.3 mm Hg, 20.6 +/- 3.7 mm Hg, 19.5 +/- 3.95 mm Hg, and 20.8 +/- 5.5 mm Hg. A significant increase in extracellular dopamine occurred after 45 minutes of deep hypothermic circulatory arrest alone, whereas in the groups of LF-20 and LF-80, the increase in dopamine did not occur until 52.5 and 60 minutes of deep hypothermic circulatory arrest, respectively.
Conclusions: The protective effect of intermittent periods of low-flow cardiopulmonary bypass during deep hypothermic circulatory arrest is dependent on the flow rate. We observed that a flow rate of 80 mL x kg(-1) x min(-1) improved brain oxygenation and prevented an increase in extracellular dopamine release.