Response of brain oxygenation and metabolism to deep hypothermic circulatory arrest in newborn piglets: comparison of pH-stat and alpha-stat strategies

Abstract

Background: To determine the effect of pH-stat as compared with alpha-stat management on brain oxygenation, level of striatal extracellular dopamine, phosphorylation, and levels of protein kinase B (Akt) and cyclic adenosine 3', 5'-monophosphate response element-binding protein (CREB), and levels of extracellular signal-regulated kinase (ERK)1/2, Bcl-2, and Bax in a piglet model of deep hypothermic circulatory arrest (DHCA).

Methods: The piglets were placed on cardiopulmonary bypass (CPB), cooled with pH-stat or alpha-stat to 18 degrees C, subjected to 90 minutes of DHCA, rewarmed, weaned from CPB, and maintained for two hours recovery. The cortical oxygen was measured by: quenching of phosphorescence; dopamine by microdialysis; phosphorylation of CREB (p-CREB), ERK (p-ERK) 1/2, Akt (p-Akt), and level of Bcl-2, Bax by Western blots.

Results: Oxygen pressure histograms for the microvasculature of the cortex show substantially higher oxygen levels during cooling and during the oxygen depletion period after cardiac arrest (up to 15 minutes) when using pH-stat compared with alpha-stat management. Significant increases in dopamine occurred at 45 minutes and 60 minutes of DHCA in the alpha-stat and pH-stat groups, respectively. The p-CREB and p-Akt in the pH-stat group were significantly higher than in the alpha-stat group (140 +/- 9%, p < 0.05 and 125 +/- 6%, p < 0.05, respectively). There was no significant difference in p-ERK1/2 and Bax. The Bcl-2 increased in the pH-stat group to 121 +/- 4% (p < 0.05) compared with the alpha-stat group. The ratio Bcl-2:Bax increased in the pH-stat group compared with the alpha-stat group.

Conclusions: The increase in p-CREB, p-Akt, Bcl-2, Bcl-2/Bax, and delay in increase of dopamine indicated that pH-stat, in the piglet model, prolongs "safe" time of DHCA and provides some brain protection against ischemic injury.

Fig 1

Effect of alpha-stat and pH-stat strategy on cortical oxygen pressure in newborn piglets during cooling and deep hypothermic circulatory arrest (DHCA). The histograms are for control (A), after 30 minutes cooling (B), 5 minutes after the start of DHCA (C), and 15 minutes after the start of DHCA (D). The oxygen pressures are corrected for the temperature of the blood at the time of measurement. The presented histograms are the means ± standard error for seven experiments. (■ = % [alpha-stat]; ○= % [pH-stat].)

Fig 2

The effect of deep hypothermic circulatory arrest (DHCA) with alpha-stat and pH-stat management on the extracellular concentrations of dopamine in striatum of newborn piglets. The three measurements of the dopamine during the pre-bypass period were averaged and the value considered as the baseline (100%). The results are means for seven alpha-stat and seven pH-stat experiments ± SD. (p < 0.05 for significant difference from alpha-stat values as determined by the Student t test; ○ = pH-stat; ■ = alpha-stat.)

Fig 3

Effect of deep hypothermic circulatory arrest (DHCA) with alpha-stat and pH-stat management on phosphorylated Akt, CREB, and ERK1/2 in the striatum of newborn piglets. (Top panel) Representative Western Blots for protein samples from DHCA with alpha-stat and pH-stat groups probed with antibodies against phosphory-lated Akt (pAkt), phosphorylated CREB (pCREB), and phosphorylated ERK1/2 (pERK1/2). (Bottom panel) The means for DHCA with pH-stat (n = 7) ± SD, expressed in % to the corresponding values obtained for the alpha-stat group (n = 7). (p < 0.05 for significant difference from alpha-stat values as determined by the Student t test.)

Fig 4

Effect of DHCA with alpha-stat and pH-stat management on N-Bax and Bcl-2 in the striatum of newborn piglets. (Top panel) Representative Western Blots for protein samples from alpha-stat and pH-stat groups probed with N-Bax or Bcl-2 antibodies. (Bottom panel) The means for DHCA with pH-stat (n =7) ± SD, expressed in % of the value obtained for alpha-stat (n =7). a p < 0.01 for significant difference from alpha-stat values as determined by Student t test.