The Critical Clock: Time-Dependent Inflammation, Catabolism and Immunosuppression Syndrome Is Associated with ICU Mortality

Background/Objectives: Chronic critical illness (CCI) is increasingly recognized as a major challenge in intensive care, yet its definition remains heterogeneous. The triad of inflammation, catabolism, and immunosuppression (ICS) is central to proposed CCI pathophysiology, but the association between its changing components and prognosis has not been systematically evaluated. We examined whether the current presence of the biomarker-defined ICS syndrome was associated with ICU mortality. Methods: In this retrospective single-center cohort study, we analyzed 820 ICU patients from the Russian Intensive Care Dataset (RICD v3.0) who had at least one episode of the biomarker-defined ICS syndrome, operationally defined by concurrent C-reactive protein > 20 mg/L, albumin < 30 g/L, and absolute lymphocyte count < 0.8 × 109/L within a 24 h period. After the index ICS syndrome event, each patient’s ICU course was classified according to the current syndrome status: ICS syndrome present (all three criteria met) or ICS syndrome absent (at least one criterion not met). We compared organ dysfunction, laboratory parameters, life-support interventions, and mortality between periods with the syndrome present and absent using linear mixed-effects models, generalized estimating equations, and time-dependent Cox regression. Mortality density was calculated per 1000 patient-days. Results: Periods with the ICS syndrome present accounted for 5271 (22.2%) of 23,796 post-index patient-days and periods with the syndrome absent accounted for 18,525 (77.8%). Variables not used to define the syndrome showed greater contemporaneous severity while the ICS syndrome was present, including higher SOFA and SOFA-2 scores, worse neurological status, lower platelet and total protein levels, and more frequent mechanical ventilation initiation (32.8% vs. 23.6%; OR: 1.59, p < 0.001). The ICS syndrome was present at the time of 133 of 243 deaths (54.7%), with a mortality density of 25.23 versus 5.94 per 1000 patient-days (IRR: 4.25, 95% CI: 3.30–5.47). In time-dependent Cox regression, the current presence versus absence of the biomarker-defined ICS syndrome was associated with a higher hazard of ICU death (unadjusted HR: 4.02, 95% CI: 2.14–7.55; adjusted HR: 3.86, 95% CI: 1.86–8.02). Conclusions: In this cohort, the current presence of the biomarker-defined ICS syndrome was associated with substantially higher ICU mortality risk than its absence. These findings support dynamic risk assessment and closer clinical evaluation; however, the biomarker combination may partly reflect contemporaneous illness severity, and the present analysis does not establish a causal effect of syndrome presence or an independent effect of cumulative prior time with the syndrome present.