Assessment of shock index in healthy cats and in cats presenting to an emergency room with shock

Objective: To prospectively compare the shock index (SI) in a population of healthy cats with a population of cats presenting to the emergency room (ER) deemed to be in a state of shock.

Design: Prospective cohort study of cats.

Setting: University teaching hospital.

Animals: Twenty-seven healthy control cats were enrolled to establish a reference interval, and 27 cats were enrolled that were presented to the ER with clinical signs of shock. Shock was defined as abnormalities in at least 2 of the following inclusion criteria: plasma lactate concentration > 2.5 mmol/L; peripheral vasoconstriction (at least 2 of the following parameters: capillary refill time >3 s, rectal-interdigital temperature gradient [RITG] >8°C, femoral pulse not palpable, pale mucous membranes); or systolic blood pressure (SBP) < 100 mm Hg.

Interventions: Upon presentation, SI (SI = heart rate [HR]/SBP), HR, SBP, and RITG were recorded in both groups, along with peripheral venous blood sampling for lactate measurement.

Measurements and main results: The mean SI in the control group was 1.47 ± 0.2 and was 1.87 ± 0.47 in the shock group (P = 0.001). Using equality in sensitivity and specificity of 0.7, an SI cutoff point of 1.54 (95% confidence interval [CI]: 0.49-0.86) was determined with an estimated area under the receiver operating characteristic curve of 0.78 (95% CI: 0.65-0.90). HR, plasma lactate concentration, and RITG did not differ between the groups. Systolic arterial blood pressure (P = 0.01), rectal temperature (P = 0.02), and interdigital temperature (P = 0.04) differed significantly.

Conclusions: The SI is a noninvasive, easy, and reliable parameter for distinguishing cats in shock from normal cats.