Clinical question: Does inclusion of two or more SIRS criteria in the definition of severe sepsis accurately identify patients with higher mortality risk, as compared with patients with infection and organ failure but with fewer than two SIRS criteria?
Background: SIRS describes dysregulation of the inflammatory response to illness. The current definition of severe sepsis includes evidence of infection, organ failure, and two or more SIRS criteria. This study sought to test the validity of inclusion of two or more SIRS criteria in the definition of severe sepsis to differentiate patients at higher mortality risk.
Being SIRS-positive independently increased the risk of death by 26%; however, modeling showed a linear relationship between mortality and presence of SIRS criteria with each additional criteria, from zero to four, increasing mortality by 13%.
Study design: 14-year, retrospective study.
Setting: One hundred seventy-two ICUs in Australia and New Zealand.
Synopsis: Investigators evaluated 109,663 patients; 87.9% had SIRS-positive severe sepsis, and 12.1% had SIRS-negative severe sepsis. Patients with SIRS-positive sepsis were younger, more ill with higher mortality, and more likely to have community-acquired infections. Both groups had decreased mortality over the 14-year study period; SIRS-positive patients decreased to 18.3% from 36.1%; SIRS-negative patients decreased to 8.5% from 27.7%.
Being SIRS-positive independently increased the risk of death by 26%; however, modeling showed a linear relationship between mortality and presence of SIRS criteria with each additional criteria, from zero to four, increasing mortality by 13%. There was no transitional increase in risk of mortality using two criteria as a cut-off.
Limiting the severe sepsis definition to two or more SIRS criteria missed one of eight patients admitted to ICU with organ failure and infection alone. SIRS-negative severe sepsis patients had significant mortality but showed similarities to SIRS-positive severe sepsis patients, suggesting they are separate phenotypes of the same condition.
Bottom line: This study challenges the sensitivity, face validity, and construct validity of the two-criteria SIRS cutoff. Redefining severe sepsis to include a lower number of SIRS criteria may diagnose more patients with organ failure and infection.
Citation: Kaukonen KM, Bailey M, Pilcher D, Cooper DJ, Bellomo R. Systemic inflammatory response syndrome criteria in defining severe sepsis. N Engl J Med. 2015;372:1629-1638.
