Lactate and hyperlactatemia revisited: an overview

In critically ill patients, elevated lactate levels are often used as a marker of illness severity. There is a vast body of literature correlating lactate with an overall worse outcome, however, it is important to remember that correlation does not necessarily imply causality. Furthermore, it is not yet clear whether giving a therapeutic implication to elevated lactate levels will improve patient outcome. Moreover, more recent literature suggests possible protective qualities of the lactate molecule against further injury. In this narrative review, we address these issues by comparing the contemporary literature to the classic view of lactate as a metabolic waste product and marker of shock severity. Firstly, the metabolism of lactate will be described. Then, the causes of elevated lactate levels are reviewed and finally, the prognostic implications of elevated lactate and the evidence surrounding the use of lactate as a guide for therapeutic interventions will be discussed. The acid-base abnormalities resulting from lactate acidosis will not be reviewed in this article.