Elevated Modified Shock Index Within 24 Hours of ICU Admission Is an Early Indicator of Mortality in the Critically Ill

Purpose: To assess whether exposure to modified shock index (MSI) in the first 24 hours of intensive care unit (ICU) admission is associated with increased in-hospital mortality. Methods: Adult critically ill patients were included in a case–control design with 1:2 matching. Cases (death) and controls (alive) were abstracted by a reviewer blinded to exposure status (MSI). Cases were matched to controls on 3 factors—age, end-stage renal disease, and ICU admission diagnosis. Results: Eighty-three cases and 159 controls were included. On univariate analysis, lorazepam administration (odds ratio [OR]: 5.75, confidence interval [CI] = 2.28-14.47; P ≤ .01), shock requiring vasopressors (OR: 3.62, CI = 1.77-7.40; P ≤ .01), maximum MSI (OR: 2.77 per unit, CI = 1.63-4.71; P ≤ .001), and elevated acute physiologic and chronic health evaluation (APACHE) III score at 1 hour (OR: 1.41 per 10 units, CI = 1.19-1.66; P ≤ .001) were associated with mortality. Maximum MSI (OR: 1.93 per unit, CI = 1.07-3.48, P = .03) and APACHE III score at 1 hour (OR: 1.29 per 10 units, CI = 1.09-1.53; P = .003) remained significant with mortality in the multivariate analysis. The optimal cutoff point for high MSI and mortality was 1.8. Conclusion: Critically ill patients who demonstrate an elevated MSI within the first 24 hours of ICU admission have a significant mortality risk. Given that MSI is easily calculated at the bedside, clinicians may institute interventions earlier which could improve survival.