Increased concentrations of L-lactate in the rectal lumen in patients undergoing cardiopulmonary bypass

Background. Gut ischaemia may contribute to morbidity in patientsafter cardiopulmonary bypass (CPB), but little is known aboutthe metabolic state of the large bowel in such patients. Thereforewe estimated the concentrations of L-lactate and in rectal mucosa in patients undergoing cardiac surgery withor without the use of CPB. Methods. Patients undergoing coronary artery bypass grafting(CABG) (n=12) or off-pump CABG (n=10) were subjected to equilibriumdialysis of the rectal lumen during the procedure and in thefirst 4 h afterwards. Dialysate concentrations of L-lactateand were measured using an auto-analyser and compared with values obtained in healthy subjects (n=10). Results. During CPB, a 2- to 3-fold increase in luminal concentrationsof L-lactate was observed (CABG vs off-pump CABG, P=0.05; CABGvs healthy subjects, P<0.01). The dialysate concentrationsof L-lactate were higher than the mean systemic values (luminal–arterialgradient mean (SD) 0.9 (1.0) mmol litre^–1, P<0.05),and the two values were positively correlated (P<0.05). LuminalL-lactate concentrations remained elevated 4 h after the operation.In contrast, dialysate was equally high in patient and control groups and substantially higher thanvalues observed in arterial blood. Conclusions. Uncomplicated CPB is associated with moderate butsustained increases in luminal concentrations of L-lactate inthe rectum, indicating metabolic dysfunction of the mucosa inthe large bowel. Part of this study was presented at the 27th Congress of theScandinavian Society of Anaesthesiology and Intensive Care Medicine,Helsinki, Finland, 2003.