Comparison of Low-Flow Cardiopulmonary Bypass and Circulatory Arrest on Brain Oxygen and Metabolism

BACKGROUND: In the neonatal brain we measured oxygen (BO2), 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 BO2 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 BO2 was between 45 to 60 mm Hg. At the end of LFCPB, BO2 was 10.5 ± 1.2 mm Hg. By 5 and 30 minutes of arrest during DHCA, BO2 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.