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

BACKGROUND: In the neonatal brain we measured oxygen (Bo(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 degrees C and underwent DHCA or LFCPB (20 mL x kg(-1) x min(-1)) for 90 minutes. The Bo(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 Bo(2) was between 45 to 60 mm Hg. At the end of LFCPB, Bo(2) was 10.5 +/- 1.2 mm Hg. By 5 and 30 minutes of arrest during DHCA, Bo(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 53000-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.