Effect of cardiopulmonary bypass on lactate metabolism

We have investigated the role of cardiopulmonary bypass on lactate metabolism in patients undergoing uncomplicated surgery for elective coronary artery bypass grafting (CABG).

Prospective non-randomized observational study.

National Cardiovascular Center. PATIENTS. Three independent groups were studied: preoperative ( n=20), postoperative with bypass (CPB, n=20) and postoperative without bypass (NO-CPB, n=20).

Lactate metabolism was investigated with the use of an exogenous lactate challenge test (2.5 mmol Na-lactate/kg body weight in 15 min). Blood lactate was sequentially determined after the end of infusion. Lactate clearance and endogenous production were estimated from the area under the curve, and a bi-exponential fitting permitted modeling the lactate-decay into two compartments.

Lactate metabolism parameters (basal lactate, clearance, endogenous production and half-lives [HL] I and II) were not different between the NO-CPB and preoperative groups. In the CPB group, as compared to the other two groups, basal lactate and endogenous production were not significantly affected while lactate clearance (CPB: 6.02+/-0.97 versus preoperative: 9.41+/-0.93 and NO-CPB: 9.6+/-0.8 ml/kg per min) and HL-I (CPB: 10.6+/-1.4 versus preoperative: 17.2+/-2.3 and NO-CPB: 18.8+/-2.5 min) were decreased ( p<0.001) and HL-II was increased (CPB: 171+/-41 versus preoperative: 73+/-12 and NO-CPB: 48+/-2.9 min, p<0.01).

While surgery and anesthesia per se do not seem to alter lactate metabolism, CPB significantly decreased lactate clearance, this effect being possibly related to a mild liver dysfunction even in uncomplicated elective surgery.