Comparison of low-flow cardiopulmonary bypass and circulatory arrest on brain oxygen and metabolism

Background In the neonatal brain we measured oxygen (B 2), extracellular striatal dopamine (DA), and striatal tissue levels of ortho-tyrosine (o-tyr) during low-flow cardiopulmonary bypass (LFCPB) or deep hypothermic circulatory arrest (DHCA) and the post-bypass recovery period. Methods Newborn piglets were assigned to sham (n = 6), LFCPB (n = 8), or DHCA (n = 6) groups. Animals were cooled to 18°C and underwent DHCA or LFCPB (20 mL • kg−1 • min−1) for 90 minutes. The B 2 was measured by quenching the phosphorescence, DA by microdialysis, and hydroxyl radicals by o-tyr levels. The results are presented as the mean ± SD (p< 0.05 was significant). Results Baseline B 2 was between 45 to 60 mm Hg. At the end of LFCPB, B 2 was 10.5 ± 1.2 mm Hg. By 5 and 30 minutes of arrest during DHCA, B 2 fell to 4.2 ± 2.5 mm Hg and 1.4 ± 0.7 mm Hg, respectively. Compared with control, extracellular DA did not change during LFCPB. During DHCA extracellular levels of DA increased, by 750-fold from baseline at 45 minutes and to a maximum of 53,000-fold at 75 minutes. After 2 hours of recovery from DHCA, the o-tyr within the striatum increased about sixfold as compared with control. There was no change in o-tyr measured after LFCPB. Conclusions In DHCA, but not LFCPB, levels of DA and o-tyr increased considerably in the striatum of piglets, a finding that may indicate the exhaustion of cellular energy levels and contribute substantially to cellular injury. Background In the neonatal brain we measured oxygen (B 2), extracellular striatal dopamine (DA), and striatal tissue levels of ortho-tyrosine (o-tyr) during low-flow cardiopulmonary bypass (LFCPB) or deep hypothermic circulatory arrest (DHCA) and the post-bypass recovery period. Methods Newborn piglets were assigned to sham (n = 6), LFCPB (n = 8), or DHCA (n = 6) groups. Animals were cooled to 18°C and underwent DHCA or LFCPB (20 mL • kg−1 • min−1) for 90 minutes. The B 2 was measured by quenching the phosphorescence, DA by microdialysis, and hydroxyl radicals by o-tyr levels. The results are presented as the mean ± SD (p< 0.05 was significant). Results Baseline B 2 was between 45 to 60 mm Hg. At the end of LFCPB, B 2 was 10.5 ± 1.2 mm Hg. By 5 and 30 minutes of arrest during DHCA, B 2 fell to 4.2 ± 2.5 mm Hg and 1.4 ± 0.7 mm Hg, respectively. Compared with control, extracellular DA did not change during LFCPB. During DHCA extracellular levels of DA increased, by 750-fold from baseline at 45 minutes and to a maximum of 53,000-fold at 75 minutes. After 2 hours of recovery from DHCA, the o-tyr within the striatum increased about sixfold as compared with control. There was no change in o-tyr measured after LFCPB. Conclusions In DHCA, but not LFCPB, levels of DA and o-tyr increased considerably in the striatum of piglets, a finding that may indicate the exhaustion of cellular energy levels and contribute substantially to cellular injury.