Decreased Circulating Red Cell Mass Induced by Intravenous Acepromazine Administration Alters Viscoelastic and Traditional Plasma Coagulation Testing Results in Healthy Horses

Coagulopathy is common in equine critical illness, with its early recognition being crucial for patient management and prognosis. In vitro viscoelastic (VE) hypercoagulability with decreased RCM/PCV has been demonstrated in dogs but not horses. Our objective was to evaluate the effects of acepromazine-induced (0.1 mg/kg IV) decreased RCM on VE and plasma coagulation parameters using a prospective interventional study of eight adult horses. Complete blood count (CBC), fibrinogen, prothrombin time (PT), partial thromboplastin time (PTT), packed cell volume (PCV), total solids (TS), and VCM Vet™ VE testing performed at baseline (T0), 1 h (T1), and 12 h (T2) post acepromazine administration. Splenic volume was determined ultrasonographically. The results were analyzed using one-way repeated measures ANOVA with Tukey's post hoc HSD test to determine the effect of time (sample). PCV decreased 13% points following acepromazine administration from T0 to T1 (<i>p</i> < 0.001), remaining decreased at T2 (<i>p</i> < 0.001). Splenic volume increased from T0 to T1 (<i>p</i> = 0.04) and was not different from baseline at T2. Maximal clot formation (MCF) increased from T0 (<i>p</i> = 0.03). PTT decreased from T0 to T1 and increased at T2 (<i>p</i> = 0.03). No other coagulation parameters were significantly altered. This study demonstrates a non-inflammatory acute model of anemia in horses that impacts VE and plasma-based testing.