Measurement of intraperitoneal metabolites during hypothermic cardiopulmonary bypass using microdialysis

Splanchnic hypoxia, with resultant mucosal acidosis during cardiopulmonary bypass (CPB) has been demonstrated using tonometry. Microdialysis is a minimally-invasive method of obtaining peritoneal fluid samples. We measured the intraperitoneal metabolites during peri-operative period following hypothermic CPB and studied the safety of intraperitoneal microdialysis.

Eleven consecutive patients undergoing coronary artery bypass grafting (CABG) were included after obtaining ethics committee approval and informed consent. Microdialysis catheters were placed intraperitoneally after sternotomy. Intraperitoneal samples and arterial blood samples were obtained peri-operatively for first 24 hours. The samples were analysed for levels of glucose, lactate, pyruvate and glycerol. Repeated measures ANOVA test was used to compare timed serum and intraperitoneal samples.

The study population included nine males and two females with a mean age of 63.7 ± 11 years. The mean CPB and X clamp times were 50.9 ± 7.3 minutes and 27.3 ± 4.9 minutes, respectively. There were no complications related to microdialysis. The intraperitoneal lactate (L), pyruvate (P) and glycerol increased during CPB and four to six hours postoperatively. The L:P ratio was >10:1 during CPB, but in the postoperative period showed evidence of impaired oxygen utilisation.

This prospective study confirms incidence of intraperitoneal anaerobic metabolism of glucose during CPB and impaired utilisation of glucose in the postoperative period. Microdialysis provides a novel and minimally-invasive method to measure real time intraperitoneal events.