Systemic inflammatory response syndrome post cardiac surgery: a useful concept?

Introduction

Systemic inflammatory response syndrome (SIRS) is the leading cause of morbidity and mortality in the critically ill. It is associated with a 50% reduction in 5-year life expectancy. SIRS is defined as two of the following criteria: heart rate >90 beats/min, respiratory rate >20 breaths/min or pCO₂ <4.3 kPa, temperature <36°C or >38°C, white cell count <4 × 10⁹/l or >12 × 10⁹/l. These criteria are used to stratify patients for specific therapies and in research to define interventional groups. Cardiac surgery is associated with systemic inflammation. We undertook to describe the incidence of SIRS post cardiac surgery and relate this to outcome.

Methods

We retrospectively analysed prospectively collected data from 2,764 consecutive admissions post cardiac surgery (coronary artery bypass grafting 1,425 admissions, valve 763 admissions, combined 252 admissions, other 324 admissions). The number of criteria met simultaneously within 1-hour epochs was recorded for the entire admissions.

Results

Totals of 96.4%, 57.9% and 12.2% of patients met at least two, three or four criteria respectively within 24 hours of admission (Table 1). The ICU mortality was 2.67%. The length of stay (LOS) exceeded 3 days in 18.5% of patients. The temperature criterion was least often fulfilled. Scoring and outcome data are presented. Simultaneous presence of more criteria was associated with greater mortality and more prolonged ICU stay, P < 0.0001.

Table 1 Scoring and outcome variables associated with meeting SIRS criteria (n = 2,764)

Conclusion

Nearly all patients fulfilled the standard two-criteria definition of SIRS within 24 hours of admission. This definition does not adequately define the subgroup of patients with greater systemic inflammation, mortality or LOS. Thus, some clinical manifestations of inflammation are very common following cardiac surgery, although not necessarily prognostic. The presence of three or more criteria was more discriminatory of death and prolonged ICU stay. We propose that three SIRS criteria is a more appropriate threshold that defines those patients with clinically significant inflammation post cardiac surgery.