Elevated Arterial Lactate Concentrations Early After Coronary Artery Bypass Grafting Are Associated With Increased Anaerobic Metabolism in Skeletal Muscle

ObjectiveTo assess the effect of coronary artery bypass grafting with cardiopulmonary bypass on muscle perfusion, oxygen extraction, and lactate release during postoperative rest and exercise.DesignProspective observational study.SettingUniversity hospital.ParticipantsPatients undergoing planned coronary artery bypass grafting.InterventionKnee-extensor exercise before and after coronary artery bypass grafting.Measurements and Main ResultsFemoral artery blood flow was measured with ultrasound. Femoral vein blood and arterial blood were sampled at rest and during light exercise and were analyzed for hemoglobin, lactate, oxygen saturation, and oxygen partial pressure.Fourteen patients were tested before and after surgery. The arterial lactate concentrations were increased after surgery, both at rest and during light exercise. Resting arterial lactate increased from 0.65 (0.5-0.8) to 1.0 (0.9-1.3) mmol/L (p = 0.01) (median and interquartile range). Furthermore, lactate was released from the leg even during postoperative rest, and the release of lactate was increased during postoperative exercise. There were no significant differences between the preoperative and postoperative femoral artery blood flow. Femoral vein oxygen partial pressure was reduced significantly after surgery, indicating reduced muscle cell oxygen partial pressure.ConclusionsThe patients had elevated anaerobic metabolism in skeletal muscle after surgery to compensate for anemia. Lactate was released from the leg into the general circulation during postoperative rest and exercise. The postoperatively reduced hemoglobin concentration of 11.4 mg/dL (10.6-12.3) resulted in increased anaerobic metabolism and release of lactate from skeletal muscle. The authors concluded that coronary artery bypass grafting patients are susceptible to anaerobic metabolism even with maintained peripheral blood flow.