Association between baseline intra-abdominal pressure and mortality risk in critically ill patients: A retrospective cohort study

Background: Abnormally elevated intra-abdominal pressure (IAP) predisposes critically ill patients to multiple organ dysfunction. Although guidelines recommend routine IAP monitoring, the relative prognostic value of baseline IAP versus dynamic changes in IAP (ΔIAP) remains controversial. In complex critical care settings, medical interventions frequently introduce confounding by indication into ΔIAP measurements. Thus, identifying stable and independent IAP predictors of adverse outcomes is essential for optimizing early risk stratification. This study aimed to determine the independent predictive value of baseline IAP and ΔIAP for mortality across various time points and overall prognosis in critically ill patients, and to assess the incremental prognostic and clinical utility of adding baseline IAP to the standard SOFA score. Methods: We included 1,440 adult critically ill patients with documented baseline IAP from the MIMIC-IV database. Patients were stratified into three groups according to baseline IAP. Kaplan-Meier analysis and multivariable Cox proportional hazards models were used to assess the independent associations of baseline IAP and ΔIAP with 7-, 28-, 90-, and 365-day all-cause mortality. Optimal prognostic cutoffs were determined using receiver operating characteristic (ROC) curves and the maximum Youden index. Subgroup analyses were performed with interaction testing, and the likelihood ratio test (LRT), C-index, and net reclassification improvement (NRI) were calculated to quantify the incremental predictive value. Results: Multivariable Cox regression analysis identified high baseline IAP (> 20 mmHg) as an independent risk factor for 7-day mortality (HR:1.378). When treated as a continuous variable, each 1-mmHg increase in baseline IAP was independently associated with a 2.6% higher risk of 7-day mortality. Conversely, ΔIAP showed no independent predictive value for early mortality. Optimal cutoff analysis demonstrated that as the observation period extended from the early (7 days) to the medium- and long-term (28–365 days), the prognostic IAP threshold for mortality shifted from 19.5 mmHg to a stable 22.5 mmHg. Subgroup analyses verified the robust predictive performance of baseline IAP across diverse clinical subgroups. Furthermore, incorporating baseline IAP into the SOFA score significantly improved model goodness-of-fit (LRT P = 0.028) and risk reclassification capacity (NRI = 0.127). Conclusions: Baseline IAP is significantly associated with time‑dependent mortality risk in critically ill patients, with early predictive utility superior to that of ΔIAP. Thus, it serves as a simple and robust predictor for early risk stratification in this population.