Objective: The aim of the study was to compare the interstitial metabolism of glucose, lactate, urea and glycerol in skeletal muscle with interstitial blood flow by microdialysis in two groups of patients undergoing cardiac surgery with a cardiopulmonary bypass (CBP) under normothermic and hypothermic conditions. Design: Prospective randomised study. Setting: Institute of Clinical Biochemistry and Diagnostics, Department of Cardiosurgery, University Hospital, Hradec Králové. Material and Methods: Microdialysis was performed in forty patients undergoing cardiac surgery with a cardiopulmonary bypass (CBP). After an institutional approval, patients were randomized into two groups. Group 1 (NT, N=20): patients were operated under normothermic condition (36 °C). Group 2 (HT, N=20): patients were operated under hypothermic conditions (32 °C). Two microdialysis (MD) probes CMA 60 (CMA Microdialysis AB) were inserted into a standard site of musculus deltoideus during introduction of anaesthesia. Microdialysis was performed with Ringer’s solution with perfusion flow 0.3 ml/hour (300 µl/hour). Microdialysis samples were collected: 0) initial phase of operation, 1) beginning of operation to beginning of CPB, 2) CPB 3) end of CPB to the end of operation, 4) 2 hours, 5) 4 hours, 6) 6 hours and 7) 8 hours after surgery. Microdialysate glucose, urea and lactate levels (mmol/l) were assessed by Hitachi 917 analyser, glycerol concentration by kit (Randox). Interstitial blood flow was monitored using flow marker gentamicin added in a known concentration in microdialysis fluid. Microdialysis gentamicin concentration was estimated by Axsym analyser (Abbott) – FPIA Method. Results: Glucose concentration in a skeletal muscle microdialysate during the 1st to the 4th intervals was higher in NT patients comparing to HT patients, and than lower. The similar applied for urea concentration. There were no significant differences in concentration of lactate and glycerol between groups. Gentamicin microdialysate concentrations were significantly higher in HT patients in comparison with NT patients at all intervals. Conclusion:We suppose that interstitial concentrations of analytes during CPBwere influenced both by blood flow changes and by metabolic changes in skeletal muscle cells. Suppression of glucose synthesis after CPB was described by other authors. There were other factors influencing interstitial metabolism, for instance dramatic changes in capillary fluid pressure and osmolality.

        Key words: microdialysis – flow marker – skeletal muscle – extracorporeal circulation