To SIRS With Love—An Open Letter

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With the advent of sepsis-3, it is important to consider whether there is still a place for the systemic inflammatory response syndrome (SIRS) (1, 2). In 1991, a conference was convened to develop consensus definitions of sepsis (3). Additionally, the term “SIRS” was coined (3) to recognize the common clinical responses and presumptive common pathophysiology seen in diverse disorders with or without infection (1, 4). SIRS patients with infections were designated as “sepsis” and those without infection as “SIRS” (2). We still need a descriptor to differentiate patients with infection from those with similar characteristics who are not infected and SIRS fulfills this role. SIRS was developed using only elementary, universally available clinical and laboratory data to facilitate early recognition of high-risk patients and to improve outcomes by expeditiously applying standard therapies and developing new innovative strategies (3). Because the SIRS criteria were developed by consensus, they were expected to require validation. Studies using two of the four SIRS criteria produced a sensitive tool for identifying septic patients (5) and validated the use of SIRS, while demonstrating increased mortality with greater sepsis severity in ICU patients (6).
Over the years, the emphasis on inflammation as the primary driver of these conditions has waned, so to keep SIRS we need a new “I” such as “illness” (systemic illness response syndrome). The adult respiratory distress syndrome was also rehabilitated from its superannuated acronym.
Some did not and still do not like SIRS (1, 2, 7). They believe that the SIRS criteria are too sensitive and lack clinical specificity (7). A study of ICU patients with presumed sepsis noted that 12% of the patients with infection, organ failure, and significant mortality did not meet SIRS criteria and thus questioned the sensitivity of the SIRS diagnosis (8). The overwhelming majority of these patients, however, still met SIRS criteria. The sepsis-3 definition is claimed to be more specific and to eliminate confusion regarding sepsis, severe sepsis, and septic shock (2). Rather than using SIRS criteria, the new definition combines infection with a “dysregulated immune response to the infection” that results in organ dysfunction as measured by a two or greater increase in the sequential, sepsis-related, organ failure assessment (SOFA) score (2). There is no reason to expect that “dysregulated immune response” would not suffer from the same obsolescence as “inflammatory” or that organ system dysfunction will be more specific in discriminating between infection and other insults than SIRS criteria. Organ system dysfunctions are not sequelae unique to infection.
The concept of SIRS has been helpful in describing the epidemiology of sepsis and evaluating the success of treatment strategies over the past 25 years (9). The median interval from SIRS to sepsis is inversely correlated with the number of SIRS criteria (6), and there is a stepwise increase in mortality rates from SIRS, sepsis, severe sepsis, and septic shock (6, 10). The prevalence of infection and bacteremia increases with the number of SIRS criteria and with increasing severity of the sepsis syndromes (10). SIRS has prognostic importance in predicting infections, severity of disease, organ failure, and survival (11–20). Patients with three or four SIRS criteria versus two have more infections and noninfected patients with greater than two SIRS criteria are more likely to develop severe sepsis and septic shock (11). Organ system failure and mortality increase with the presence and number of SIRS criteria (11–16, 19, 20).
SIRS, as initially hoped, has demonstrated utility in diseases other than sepsis. The occurrence of SIRS in patients with subarachnoid hemorrhage is associated with higher mortality and morbidity rates (13).
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