Ph-stat versus alpha-stat perfusion strategy during experimental hypothermic circulatory arrest: a microdialysis study

Background The superiority of the pH-stat to the α-stat acid-base strategy during cardiopulmonary bypass as a neuroprotective method during hypothermic circulatory arrest is still controversial. In the present study, brain metabolism and outcome have been evaluated in a surviving model of experimental hypothermic circulatory arrest. Methods Twenty pigs undergoing 75-minutes of hypothermic circulatory arrest at a brain temperature of 18°C were randomly assigned to the α-stat (n = 10) or pH-stat (n = 10) strategy during cardiopulmonary bypass. Results The 7-day survival rate was 90% (9 of 10) in the pH-stat group and 10% (1 of 10) in the α-stat group. At the end of cooling, pH-stat strategy was associated with significantly lower brain lactate and pyruvate concentrations and brain lactate-glucose ratio. After reperfusion, brain concentrations of glycerol, lactate, pyruvate, and lactate-glucose ratio were significantly lower in the pH-stat group. This strategy was associated with a faster rise of brain tissue temperature and reoxygenation on reperfusion, which is likely secondary to improved cerebral perfusion. Conclusions During cardiopulmonary bypass before and after a period of hypothermic circulatory arrest, acid-base management according to the pH-stat principles seemed to be associated with less derangements in cerebral metabolism, lower intracranial pressures, and excellent behavioral recovery and survival outcome. Because there is strong evidence of the beneficial metabolic effects related to this method, further studies using an experimental model of combined HCA and embolic brain injury are required to exclude a possible increased risk of cerebral embolism associated with the pH-stat strategy.