[Relationship between "1-hour serum lactate" level and 30-day mortality in critical care patients in intensive care unit].

Objective: To investigate the relationship between 1-hour lactate (1 h Lac) and 30-day mortality in critical care patients in intensive care unit (ICU).

Methods: A retrospective, observational cohort study was performed with adult critical patients (age ≥ 16 years old) having lactate records within 1 hour after ICU admission from Medical Information Mart for Intensive Care-III database (MIMIC-III). According to the 1 h Lac level, the patients were divided into three groups: < 2 mmol/L, 2-4 mmol/L, and > 4 mmol/L groups. The baseline characteristics were analyzed. Multivariable Logistic regression analysis was performed to assess the association between 1 h Lac and 30-day mortality. The receiver operating characteristic (ROC) curve was used to analyze the predictive value of 1 h Lac for 30-day mortality, and Kaplan-Meier survival curve was performed according to the best cut-off value. In addition, sensitivity analysis was carried out for each classification variable.

Results: A total of 3 969 ICU patients were included, with 673 died in 30 days, and the total mortality was 16.95%. There were 1 664, 1 588, 717 patients in Lac < 2 mmol/L, 2-4 mmol/L and > 4 mmol/L group, respectively. There were significant differences in age, ICU duration, ICU type, heart rate, leukocyte count, hemoglobin, creatinine, sequential organ failure score (SOFA), ventilator application, vasoactive drug use and main diagnosis among the three groups. Multivariable Logistic regression analysis showed that a 1 mmol/L increment in Lac was associated with 0.24 times higher risk of 30-day mortality [odds ratio (OR) = 1.24, 95% confidence interval (95%CI) was 1.19-1.29, P < 0.000 1]. ROC curve analysis showed that the area under ROC curve (AUC) of 1 h Lac for predicting 30-day mortality of severe patients was 0.694 (95%CI was 0.669-0.718). The cut-off value was 3.35 mmol/L with sensitivity of 0.499 and specificity of 0.779, whilst positive likelihood ratio was 2.260, and negative likelihood ratio was 0.643. According to the cut-off value of 1 h Lac, the patients were divided into high lactate group (≥ 3.35 mmol/L) and low lactate group (< 3.35 mmol/L). In the two subgroups, 30-day mortality was 31.58% (336/1 064) and 11.60% (337/2 905), respectively. The Kaplan-Meier survival curve showed that the 30-day cumulative survival rate of high lactate group was significantly lower than that of low lactate group (Log-rank test: χ = 247.72, P < 0.000 1). Multiple Logistic regression analysis showed that the 30-day mortality rate of high lactate group was 2.34 times that the level of low lactate group (OR = 2.34, 95%CI was 1.90-2.88, P < 0.000 1), after the adjustment of age, time of admission, type of ICU, hemoglobin, leukocyte count, use of vasopressor, use of ventilator and main diagnosis of patients. Stratified analysis showed that the relationship between 1 h Lac and 30-day mortality was stable.

Conclusions: 1 h Lac is associated with 30-day mortality in critical care patients. The risk of death was significantly increased in critically ill patients with 1 h Lac higher than 3.35 mmol/L.