Comparison of pH-stat and alpha-stat cardiopulmonary bypass on cerebral oxygenation and blood flow in relation to hypothermic circulatory arrest in piglets

Background: Deep hypothermic circulatory arrest is used in neonatal cardiac surgery. Recent work has suggested improved neurologic recovery after deep hypothermic arrest with PH-stat cardiopulmonary bypass (CPB) compared with alpha-stat CPB. This study examined cortical oxygen saturation (Sc-O2), cortical blood flow (CBF), and cortical physiologic recovery in relation to deep hypothermic arrest with alpha-stat or pH-stat CPB. Methods: Sixteen piglets were cooled with pH-stat or alpha-stat CPB to 19 degrees C (cortex) and subjected to 60 min of circulatory arrest, followed by CPB reperfusion and rewarming and separation from CPB, Near infrared spectroscopy and laser Doppler flowmetry were used to monitor Sc-O2 and CBF, Cortical physiologic recovery was assessed 2 h after the piglets mere separated from CPB by cortical adenosine triphosphate concentrations, cortical water content, CBF, and Sc-O2. Results: During CPB cooling, Sc-O2 increased more with pH-stat than with alpha-stat bypass (123 +/- 33% vs. 80 +/- 25%); superficial and deep CBF were also greater with pH-stat than with alpha-stat bypass (22 +/- 25% ys, -56 +/- 22%, 3 +/- 19% vs. -29 +/- 28%). During arrest, Sc-O2 half-life was greater with pH-stat than with alpha-stat bypass (10 +/- 2 min vs. 7 +/- 2 min), and cortical oxygen consumption lasted longer with PH-stat than with alpha-stat bypass (36 +/- 8 min vs, 25 +/- 8 min). During CPB reperfusion, superficial and deep CRF were less with alpha-stat than with pH-stat bypass (-40 +/- 22% vs: 10 +/- 39%, -38 +/- 28% vs. 5 +/- 28%), After CPB, deep cortical adenosine triphosphate and CBF were less with alpha-stat than with pH-stat bypass (11 +/- 6 pmole/mg us. 17 +/- 8 pmole/mg, -24 +/- 16% vs, 16 +/- 32%); cortical mater content was greater with alpha-stat than with pH-stat bypass (superficial: 82.4 +/- 0.3% vs. 81.8 +/- 1%, deep: 79.1 +/- 2% vs. 78 +/- 1.6%). Conclusions: Cortical deoxygenation during hypothermic arrest was slower after pH-stat CPB, PH-stat bypass increased the prearrest Sc-O2 and arrest Sc,, half-life, to increase the cortical oxygen supply and slow cortical oxygen consumption. Improved cortical physiologic recovery after hypothermic arrest was suggested with pH-stat management.