A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether pH–stat or alpha–stat is the best technique to follow in patients undergoing deep hypothermic circulatory arrest. Altogether 206 papers were found using the reported search, of which 16 represent the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. Excluding one paper which provided inconclusive results, six studies found better cerebrovascular metabolism with alpha–stat while three studies found better cerebrovascular metabolism with pH–stat. Four other studies showed no significant difference in the cerebrovascular metabolism between the two acid-base management strategies in patients undergoing deep hypothermic circulatory arrest. Nine studies compared the neuropsychological outcome in patients who underwent deep hypothermic circulatory arrest with three studies supporting each alternative conclusion of preference towards alpha–stat or pH–stat management. The remaining three studies showed no significant difference between the two groups of acid-base management. Comparing the 16 studies based on the age of the patients studied, three out of the four papers which demonstrated that the pH–stat method is a better strategy to improve intraoperative and postoperative outcome were based on a sample of paediatric patients. Conversely, all seven papers that suggested alpha–stat method is associated with better intraoperative and postoperative outcome were based on studies done on adult patients. The remaining four papers suggested no significant difference between the pH–stat group and alpha–stat group. In conclusion, there is evidence to suggest that the best technique to follow in the management of acid-base in patients undergoing deep hypothermic circulatory arrest during cardiac surgery is dependent upon the age of the patient with better results using pH–stat in the paediatric patient and alpha–stat in the adult patient.
