Lactate: an unusually sensitive parameter of ensuing organ failure?

To the Editor: With interest we read the article on the association among blood lactate levels, Sequential Organ Failure Assessment subscores, and mortality by Jansen et al (1). Their retrospective results indeed suggest blood lactate levels are related to Sequential Organ Failure Assessment scores, particularly during the early phase of an intensive care unit (ICU) stay. Although the findings of Jansen et al are interesting, we would like to raise some concerns. First, the authors demonstrated differences in outcome based on area under the lactate curve (AUC) between survivors and nonsurvivors. The upper normal lactate limit was defined as 2.0 mmol/L, which was also used to compute the AUC. In survivors (n 105), the median AUC was 0 for all used lactate values (initial, maximal, total, and mean lactate). In nonsurvivors (n 29), the median AUC varied between 0 and 0.5, including the AUC of total lactate (AUC, 0.5; interquartile range, 0–2.7). We assume that the units used in this table are days/mmol/L. To understand the real lactate load, we also assumed the median length of stay in the ICU of nonsurvivors equaled the median ICU length of stay of the total population (2.75 days). This means a median total lactate load of only 2.2 mmol/L during 1 day in nonsurvivors. We think it hard to understand these values in relation to the reported differences in clinical outcome. If such a small level above the upper normal limit would mean such a strong difference in outcome, we should consider a large abasement of the normal upper limit. That is unlikely to happen. On the other hand, the AUC might prove to be an extremely sensitive parameter. Indeed, shorter duration of hyperlactemia (“lactime”) (2) and higher lactate clearance (3) are important, but if we overpraise lactate as a prognostic parameter, we would neglect the complexity of the origin of lactate both in general and in critically ill patients (4, 5). Second, Jansen et al described a clinically relevant association in the early phase of ICU stay between failure of the cardiovascular system and lactate-derived parameters. They suggested that hyperlactatemia in critically ill ICU patients illustrates the severity of the initial cardiovascular collapse. This may indicate the presence of hypoperfused organ systems without simultaneous global hypotension (6, 7). However, the Sequential Organ Failure Assessment cardiovascular subscore is not only determined by systolic blood pressure (mm Hg), but also by the use of vasopressors (in g/kg/min). The difference in use of vasopressors between survivors and nonsurvivors is not obvious from the presented data. This is unfortunate, because others have prospectively shown that patients with higher lactate clearance had favorable outcome but with inconsistent differences in either the use of vasopressors in survivors compared with nonsurvivors or patient assigned to standard therapy or early goal-directed therapy (3, 8). We agree with the authors that prospective studies are needed to improve insight in the causal relationship between hyperlactemia and individual organ dysfunction. The authors have not disclosed any potential conflicts of interest.