Lactate in the intensive care unit: pyromaniac, sentinel or fireman?

Lactate is certainly not a pyromaniac: it is not toxic and possesses no harmful effect per se. It is probably a trustworthy sentinel because it sensitively indicates that fire is potentially in the house and numerous works have already shown a good relationship between lactate level and outcome [1]. Above all, it is an indispensable soldier that actively acts as a major intermediate involved in the vast cellular and organ energy interplay, allowing the body to cope with a wide range of metabolic disorders (for example, exercise, hypoxia, ischemia, severe sepsis, shock) [2].Based on their broad experience in the management of the profound metabolic derangements observed in critical illnesses, associated with some experimental data, Valenza et al. [3] propose, in a review-hypothesis paper in this issue of Critical Care, to regard lactate increase in the intensive care unit as a marker of a metabolic adaptation requiring a therapeutic aid ("possibly indicating that 'there is still room' to boost fast intervention") rather than a sign of irreversible end-stage energy failure. In this context, these authors propose to take the decrease in blood lactate following a therapeutic challenge as a major indicator of the efficacy of such treatment. This proposal seems absolutely correct and very close to what has been already proposed regarding oxygen consumption (VO2), but with a simple bedside parameter of metabolic integration. Indeed, whatever the cause of derangement and the metabolic environment, any rise in blood lactate indicates an attempt by the body to adapt to an unusual energetic situation, which may affect redox state, phosphate potential or pH [4]. Moreover, as indicated by the authors, lactate production requires a complete glycolytic pathway, that is, an intact cell with sufficient glucose supply or glycogen storage. Therefore, in ischemic tissues, which don't have a sustained supply of blood glucose, a substantial amount of lactate can be released as long as gl