Echocardiographic effects of medetomidine, butorphanol, and their combination in donkeys

Standing sedation is frequently required in donkeys for minor surgical and diagnostic procedures, yet information on the cardiac safety of α2-adrenoceptor agonists and opioid combinations in this species is limited. This study evaluated the echocardiographic effects of intravenous medetomidine, butorphanol, and their combination in clinically healthy donkeys.

Sixty donkeys were randomly assigned to four groups (n = 15/group) to receive intravenous saline (control group, CG), medetomidine group (10 µg/kg, MG), butorphanol group (50 µg/kg, BG), or medetomidine-butorphanol group (10 µg/kg + 50 µg/kg, MBG). Butorphanol was administered 5 min after medetomidine in the MBG. M-mode echocardiography was performed from a right parasternal short-axis view at baseline and at 5, 15, 30, 45, 60, 90, and 120 min after treatment. Left ventricular internal diameter (LVID), interventricular septal thickness (IVST), and left ventricular posterior wall thickness (LVPW) were measured at end-diastole (d) and end-systole (s). Left ventricular end-diastolic volume (LVEDV), left ventricular end-systolic volume (LVESV), stroke volume (SV), ejection fraction (EF%), and fractional shortening (FS%) were calculated. Data were analyzed using a repeated-measures general linear model.

Medetomidine alone was associated with significant reductions in EF% and FS%, together with significant changes in LVIDs and LVIDd. SV was also significantly lower in the medetomidine group than in the control group during the main post-treatment period; however, SV and the calculated LV volumes were interpreted cautiously because they are load-dependent variables derived from linear M-mode measurements. These changes were accompanied by an increase in LVIDs and a reduction in IVSs, indicating transient depression of conventional left ventricular systolic indices and altered loading conditions. Butorphanol alone produced only minor, parameter-specific changes in LVID, IVST, and most echocardiographic indices, with no consistent clinically relevant deterioration compared with baseline or the CG. In contrast, the MBG showed marked changes in ventricular dimensions and calculated indices from 15 to 60 min; however, these findings were interpreted cautiously because the calculated systolic indices are load-dependent.

Intravenous medetomidine, butorphanol, and their combination exert distinct and protocol-dependent effects on left ventricular dimensions and systolic function in donkeys. Medetomidine alone substantially and transiently depresses systolic performance, whereas butorphanol alone is comparatively cardiovascular-sparing. The medetomidine-butorphanol combination may be considered for standing sedation in clinically healthy donkeys; however, its echocardiographic effects should be interpreted cautiously as load-dependent changes, and cardiovascular monitoring remains advisable.