Lactate-bicarbonate ratio as an early predictor of 28-day mortality among critically ill children with pneumonia and acute kidney injury

Background and aim: Pneumonia complicated by acute kidney injury (AKI) is a high-risk phenotype in critically ill children, but simple early prognostic markers remain limited. We evaluated whether the lactate-bicarbonate ratio (LBR) within 24 hours of ICU admission was associated with 28-day mortality and explored its dose-response relationship and a useful cutoff for early risk stratification. Methods: This retrospective single-center cohort study included 325 non-neonatal critically ill children with pneumonia and acute kidney injury. The primary exposure was the maximum paired LBR within the first 24 hours after ICU admission. The association between early LBR and 28-day mortality from ICU admission was assessed using Cox proportional hazards regression and restricted cubic splines. Results: Among 325 children, 44 (13.5%) died within 28 days; 320 (98.5%) had at least one valid lactate-bicarbonate pair. Compared with survivors, non-survivors were younger, had more severe AKI, lower pH, higher anion gap, lower PaO2, and higher early lactate and paired LBR, whereas bicarbonate alone did not differ significantly. Higher maximum paired LBR was independently associated with 28-day mortality (adjusted HR per 0.1-unit increase, 1.034; 95% CI, 1.013–1.054), showed a significant non-linear association, and a cutoff of 0.237 identified a small high-risk subgroup with markedly higher mortality. Conclusions: Early LBR may aid risk stratification, pending external validation.