Systemic Inflammatory Response Syndrome Criteria in Defining Severe Sepsis

TLDR

Severe sepsis is defined by infection, organ failure, and at least two systemic inflammatory response syndrome (SIRS) criteria. The study aimed to evaluate the sensitivity, face validity, and construct validity of using two or more SIRS criteria to define severe sepsis. Using a multicenter cohort of 1,171,797 ICU patients from Australia and New Zealand (2000–2013), the authors identified those with infection and organ failure and classified them as SIRS-positive (≥2 criteria) or SIRS-negative (<2 criteria), then compared their characteristics, outcomes, and mortality risk across the SIRS threshold. Among 109,663 patients with infection and organ failure, 87.9% were SIRS-positive and 12.1% SIRS-negative, both groups had comparable characteristics and declining mortality over 14 years, and mortality rose linearly with each additional SIRS criterion without a distinct risk jump at two criteria, indicating the threshold excluded many patients without a transition in death risk. The study was funded by the Australian and New Zealand Intensive Care Research Centre.

Abstract

The consensus definition of severe sepsis requires suspected or proven infection, organ failure, and signs that meet two or more criteria for the systemic inflammatory response syndrome (SIRS). We aimed to test the sensitivity, face validity, and construct validity of this approach.We studied data from patients from 172 intensive care units in Australia and New Zealand from 2000 through 2013. We identified patients with infection and organ failure and categorized them according to whether they had signs meeting two or more SIRS criteria (SIRS-positive severe sepsis) or less than two SIRS criteria (SIRS-negative severe sepsis). We compared their characteristics and outcomes and assessed them for the presence of a step increase in the risk of death at a threshold of two SIRS criteria.Of 1,171,797 patients, a total of 109,663 had infection and organ failure. Among these, 96,385 patients (87.9%) had SIRS-positive severe sepsis and 13,278 (12.1%) had SIRS-negative severe sepsis. Over a period of 14 years, these groups had similar characteristics and changes in mortality (SIRS-positive group: from 36.1% [829 of 2296 patients] to 18.3% [2037 of 11,119], P<0.001; SIRS-negative group: from 27.7% [100 of 361] to 9.3% [122 of 1315], P<0.001). Moreover, this pattern remained similar after adjustment for baseline characteristics (odds ratio in the SIRS-positive group, 0.96; 95% confidence interval [CI], 0.96 to 0.97; odds ratio in the SIRS-negative group, 0.96; 95% CI, 0.94 to 0.98; P=0.12 for between-group difference). In the adjusted analysis, mortality increased linearly with each additional SIRS criterion (odds ratio for each additional criterion, 1.13; 95% CI, 1.11 to 1.15; P<0.001) without any transitional increase in risk at a threshold of two SIRS criteria.The need for two or more SIRS criteria to define severe sepsis excluded one in eight otherwise similar patients with infection, organ failure, and substantial mortality and failed to define a transition point in the risk of death. (Funded by the Australian and New Zealand Intensive Care Research Centre.).