Prognostic value of the shock index and modified shock index in survivors of out-of-hospital cardiac arrest: A retrospective cohort study

Abstract

Background: There is a lack of rapid, non-invasive tools that aid early prognostication in patients with return of spontaneous circulation (ROSC) after Out-of-Hospital Cardiac Arrest (OHCA). The shock index (SI) and modified shock index (MSI) have shown to be useful in several medical conditions, including myocardial infarction. In this study, we assessed the prognostic value of SI and MSI at Emergency Department (ED) triage on survival to discharge of OHCA patients.

Methods: A single-center retrospective observational cohort study. All OHCA patients with a period of ROSC between 2014 and 2019 were included. Data collection was based on the Utstein criteria. The SI and MSI at ED triage were calculated by dividing heart rate by systolic blood pressure or mean arterial pressure. Survival rates were compared between patients with a high and low SI and MSI. Subsequent Cox regression analysis was performed.

Main results: A total of 403 patients were included, of which 46% survived until hospital discharge. An elevated SI and MSI was defined by SI ≥ 1.00 and MSI ≥ 1.30. Survival to discharge, 30-day- and one-year survival were significantly lower in patients with an elevated SI and MSI (p < 0.001). An elevated SI and MSI was also associated with a higher rate of recurrent loss of circulation in the ED (p < 0.001). The 30-day survival hazard ratio was 2.24 (1.56-3.22) for SI and 2.46 (1.71-3.53) for MSI; the one-year survival hazard ratio was 2.20 (1.54-3.15) for SI and 2.38 (1.66-3.40) for MSI.

Conclusion: Survival to discharge and 30-day survival are lower in OHCA patients with an elevated SI and MSI at ED triage. Further studies are warranted to elucidate the causational mechanisms underlying the association between elevated SI or MSI and worse outcomes.

Keywords: Modified shock index; Out-of-hospital cardiac arrest; Prognosis; Resuscitation; Shock index; Survival.