Clinicians discovered and began using lactate as a biomarker in the mid-1800s. Yet, its utility as a clinical tool continues to vex modern-day physicians. Although an increasing amount of literature has shown that elevations in lactic acid are generally unfavorable, 1-4 the underlying etiology, how to treat, and how to prevent increases in lactate remain elusive. In this month's Journal of Cardiothoracic and Vascular Anesthesia, Govender et al. 5 used intraoperative lactic acid concentration as a dynamic variable to be assessed during cardiac surgery. Cardiopulmonary bypass (CPB) is arguably one of the most precarious interventions in medicine, as it calls for meticulous attention to fluid composition, appropriate delivery of oxygen, and acid-base balance. Unlike previous investigators, Govender, et al. analyzed the change in intraoperative lactate levels, independent of the initial value, and associations with adverse outcomes. Hyperlactatemia can result from anaerobic or aerobic pathways and occurs when there is excess production or decreased clearance of lactate. 6,7 It occurs in nearly two-thirds of patients undergoing cardiac surgery. 1 Lactic acidosis has been separated broadly into 2 types: A and B. Type A lactic acidosis accounts for most clinical presentations and results when oxygen delivery is insufficient, such as during hypovolemia, blood loss, sepsis, and cardiogenic shock. 7 Whether a global or regional oxygen debt exists, the hypoxic conditions result in anaerobic metabolism. In this scenario, a glycolytic pathway much less efficient than the citric acid cycle ensues with lactic acid produced as a byproduct. Alternatively, during aerobic conditions accelerated metabolism owing to stress or inotropic medications can overwhelm the pyruvate dehydrogenase enzyme, leaving pyruvate to be broken down into lactate instead of acetyl-coenzyme A. This is known as type B lactic acidosis. Type B lactic acidosis also can be caused by medications, malignancies, malnutrition, or congenital errors in metabolism, among others. 7 Furthermore, epinephrine, which commonly is used in cardiac surgery, increases hepatic degree of lactate rise directly correlated with 30-day mortality.
