The association between lactate trajectories and prognosis in ICU patients with pneumonia: A retrospective...

ObjectiveTo identify pneumonia-specific lactate trajectory phenotypes and evaluate their association with 28-day mortality in ICU patients with pneumonia.MethodsA retrospective cohort study was performed using the MIMIC-IV database. Adult ICU patients with pneumonia were identified via ICD-9/10 codes. Exclusions were non-index ICU admissions, age <18 or >100 years, ICU stay <3 days, and incomplete lactate data in the first 72 hours. Demographics, vital signs, laboratory results, comorbidities, severity scores, and treatments were extracted. Group-based trajectory modeling (GBTM) was applied to lactate values over 72 hours. Model selection considered BIC, AIC, average posterior probability (AvePP), odds of correct classification (OCC), class size, and clinical interpretability. Outcomes included 28-day all-cause mortality (primary) and secondary endpoints. Kaplan-Meier analysis and Cox regression were used to examine associations, with subgroup analyses across demographic and clinical strata.ResultsA total of 2,091 patients were included. Four distinct lactate trajectories were identified: low-stable (n=1161), moderate with gradual decline (n=721), initial rise then decline (n=89), and very high with rapid decline (n=120). Unfavorable trajectory classes were associated with greater illness severity, metabolic derangements, resource use, and higher mortality. As a continuous variable, lactate showed a borderline association with 28-day mortality in unadjusted analysis (HR 1.03, 95% CI 1.00-1.05, p=0.082), but lost significance after adjustment. In contrast, trajectory-based groups remained independently associated with outcomes: fully adjusted HRs were 1.30 (95% CI 1.08-1.56, p=0.004) for class 2, 1.49 (95% CI 1.03-2.15, p=0.034) for class 3, and 1.71 (95% CI 1.20-2.45, p=0.003) for class 4. Subgroup analyses showed consistent associations, with a stronger effect in patients <65 years (p for interaction=0.033).ConclusionsIn ICU patients with pneumonia, 72-hour lactate trajectory phenotypes were independently associated with 28-day mortality and may help characterize prognostic heterogeneity, including delayed lactate elevation patterns not captured by admission lactate alone.