Prognostic Value and Development of a Scoring System in Horses With Systemic Inflammatory Response Syndrome

Abstract

Background: Despite its widespread use in equine medicine, the clinical value of the systemic inflammatory response syndrome (SIRS) concept in horses remains unknown.

Objectives: To study the prognostic value of measures of SIRS in horses and identify the best model of severe SIRS to predict outcome.

Animals: A total of 479 consecutive adult horse emergency admissions to a private primary referral practice.

Methods: Prospective observational study. All adult horses admitted for emergency treatment over the study period were included. Multivariate logistic regression and stepwise model selection were used.

Results: Each of the 4 SIRS criteria was associated with outcome in this population. Thirty-one percent of emergency cases had 2 or more abnormal SIRS criteria on admission and were defined as SIRS cases. SIRS was associated with increased odds of death (odds ratio [OR] = 8.22; 95% CI, 4.61-15.18; P < .001), an effect mainly found for acute gastrointestinal cases. SIRS cases were assigned a SIRS score of 2, 3, or 4, according to the number of abnormal SIRS criteria fulfilled on admission, and SIRS3 and SIRS4 cases had increased odds of death compared to SIRS2 cases (OR = 4.45; 95% CI, 1.78-11.15; P = .002). A model of severe SIRS including the SIRS score, blood lactate concentration, and color of the mucous membranes best predicted outcome in this population of horses.

Conclusions and clinical importance: Systemic inflammatory response syndrome is associated with an increased risk of death in adult horses presenting with acute gastrointestinal illnesses. The model of severe SIRS proposed in this study could be used to assess the status and prognosis of adult equine emergency admissions.

Keywords: Equine; Lactate; Mucous membranes; Outcome.

Figure 1

Admission values for the systemic inflammatory response syndrome criteria, comparing cases that survived with cases that died. Individual values, median, and interquartile range are shown. (A) n = 438; (B) n = 421; (C) n = 386; (D) n = 307. Mann–Whitney test, **P < .001; *P = .027.

Figure 2

Kaplan–Meir survival curves, comparing systemic inflammatory response syndrome (SIRS) cases and non‐SIRS cases. The survival curves are significantly different. Log‐rank test, P < .001. The graph shows survival up to 25 days. Seven cases that stayed in the clinic for more than 25 days (up to 108 days) are not shown on this graph but were included in the analysis.

Figure 3

Systemic inflammatory response syndrome (SIRS) score. (A) The case fatality rate increases with increasing number of abnormal SIRS criteria (SIRS score). Chi‐square test for trend, P < .001 (chi‐square = 79.57, df = 1). The case fatality rates as well as the number of death and the total number of horses in each group are shown above the bars. (B) Kaplan–Meier survival curves for different SIRS score groups. The survival curves are significantly different, and median survival is found to decrease with increasing SIRS score (log‐rank test for trend, P < .001). All pairwise comparisons are also significantly different (Bonferroni‐corrected threshold: P = .008) except for the SIRS3 versus SIRS 4 pairwise comparison. Log‐rank tests: non‐SIRS versus SIRS2: P = .001; non‐SIRS versus SIRS3: P < .001; non‐SIRS versus SIRS4: P < .001; SIRS2 versus SIRS3: P = .003; SIRS2 versus SIRS4: P = .003; SIRS3 versus SIRS4: P = .581. Survival shown up to 25 days. Five cases that stayed in the clinic for more than 25 days (up to 108 days) are not shown on this graph but were included in the analysis.

Figure 4

Receiver operating characteristic curves showing the performance of the various models of severe systemic inflammatory response syndrome (SIRS) in predicting outcome in adult equine emergency admissions. SIRS score: number of abnormal SIRS criteria fulfilled among the following: heart rate >52 bpm, respiratory rate >20 bpm, temperature below or above 37.0–38.5°C, WBC above or below 5.0–12.5 × 10⁹/L. MM: mucous membranes. The mucous membranes were considered abnormal if they were described as bright pink, injected, purple, muddy, toxic, red, or white.