20 Years On: Is It Time to Redefine the Systemic Inflammatory Response to Cardiothoracic Surgery?

The “systemic inflammatory response” has never been defined from a cardiothoracic surgery perspective, but borrowed its definition from the critical care field at a landmark 1992 definition conference on sepsis. It is unclear why the diagnostic criteria for the Systemic Inflammatory Response Syndrome (SIRS) were adopted in isolation, ignoring other potentially more useful definitions for Severe Septic Shock or Secondary Multiple Organ Dysfunction Syndrome. The 1992 SIRS definition for sepsis has since been updated at a conference in 2001 advocating PIRO (Predisposition, Infection, host Response, Organ dysfunction) as a hypothetical model to better link sepsis with clinical outcome. PIRO is readily adaptable to cardiothoracic surgery and provides the precedent and road map for how to update a definition. The need is obvious since the current definition of SIRS is widely disregarded in heart surgery: a dwindling proportion (14%) of articles on the systemic inflammatory response even mention SIRS and 0% monitored SIRS criteria in the past decade in an evidence-based review of anti-inflammatory interventions. The name “inflammatory response” is also problematic; it is too narrow and might be replaced with host response (the R in PIRO) to better convey the wide spectrum of host defensive pathways activated during heart surgery (i.e., complement, coagulation, fibrinolysis, kinins, cytokines, proteases, hemolysis, oxidative stress). A variant on PIRO could allow these elements of the host Response (R) to be anchored within the context of Premorbid conditions (P) and the inevitable Insult (I) from surgery, to better link risk exposures to Organ dysfunction (O) in heart surgery. The precedent of PIRO suggests the following steps will be required to redefine the systemic inflammatory response: 1) buy-in from the leading societies for cardiothoracic surgery, anesthesia, and perfusion on the need for a re-definition conference, 2) assigning relative risk scores to different premorbid exposures, operative insults, and host response factors on clinical outcome, 3) validation of the risk model in a prospective cohort, and 4) development of algorithms or “apps” to facilitate rapid diagnosis and staging of care at bedside.