The Relation between Skeletal Muscle Blood Flow and Selected Parameters of Metabolismduring Cardiac Surgery with Cardiopulmonary Bypass

Overview

Objective:
The aim of the study was to compare the interstitial metabolism of glucose, lactate, urea and glycerol in skeletalmuscle with interstitial blood flow by microdialysis in two groups of patients undergoing cardiac surgery with a cardiopulmonarybypass (CBP) under normothermic and hypothermic conditions.Design: Prospective randomised study.Setting: Institute of Clinical Biochemistry and Diagnostics, Department of Cardiosurgery, University Hospital, HradecKrálové.Material and Methods: Microdialysis was performed in forty patients undergoing cardiac surgery with a cardiopulmonarybypass (CBP). After an institutional approval, patients were randomized into two groups. Group 1 (NT, N=20): patients wereoperated 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 musculusdeltoideus during introduction of anaesthesia. Microdialysis was performed with Ringer’s solution with perfusion flow 0.3ml/hour (300 µl/hour). Microdialysis samples were collected: 0) initial phase of operation, 1) beginning of operation tobeginning 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 bykit (Randox). Interstitial blood flow was monitored using flow marker gentamicin added in a known concentration inmicrodialysis 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 NTpatients comparing to HT patients, and than lower. The similar applied for urea concentration. There were no significantdifferences in concentration of lactate and glycerol between groups. Gentamicin microdialysate concentrations weresignificantly 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 changesand by metabolic changes in skeletal muscle cells. Suppression of glucose synthesis after CPB was described by otherauthors. There were other factors influencing interstitial metabolism, for instance dramatic changes in capillary fluidpressure and osmolality.

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