An evaluation of the shock index in cats with hypoperfusion; a novel, pilot study

Abstract

Introduction: Identification of shock in cats can be challenging. The Shock Index (SI) has been evaluated in human and canine emergency medicine and found to be a useful index for identification of shock. It is calculated as the heart rate/systolic blood pressure. Studies in dogs have shown that a value of >=0.9 maximises the sensitivity and specificity when combined with clinical signs for identifying shock. To the authors' knowledge the SI has not been previously evaluated in cats. Objective(s): To define the SI value in cats, and compare this value between cats presenting with and without clinical signs of hypoperfusion. Method(s): Cats presenting as emergencies between January 2014 and July 2015 were identified retrospectively. Cats with insufficient recorded data to identify hypoperfusion, or did not include heart rate and systolic blood pressure on presentation were excluded. Cats were divided into a hypoperfused and control group based on clinicopathological findings and clinician diagnosis. Age, body weight, heart rate and systolic blood pressure were analysed using Independent Sample T-tests. An Independent Kruskal-Wallis test was used to compare the SI between the groups. The SI was calculated for each cat and a receiver operating characteristics curve was used to determine the area under the curve to identify the optimum cut off value for maximising sensitivity and specificity of the SI. This SI value was then applied prospectively to 10 cats presenting emergently between July and October 2015. Result(s): Sixty-three cats (16 hypoperfused and 47 controls) met the inclusion criteria. Age, body weight and heart rate did not differ between the groups. Systolic blood pressure was lower ( =1.6 with a sensitivity/ specificity of 75% and 86% respectively. When this was applied to the prospective group 75% of cats presenting with clinical signs indicating hypoperfusion had a SI >=1.6. Overall a SI >=1.6 was associated with higher mortality. Conclusion(s): The SI is a rapid, simple, ancillary tool and when combined with clinical findings can aid in identifying most cats presenting with hypoperfusion. A SI >=1.6 is suggested as a cut off value for identification of hypoperfusion and warrants prospective investigation. In this population a SI >=1.6 was associated with higher mortality.