Cardiovascular Effects of Dobutamine and Phenylephrine Infusion in Sevoflurane-anesthetized Thoroughbred Horses

Abstract

To determine dose-dependent cardiovascular effects of dobutamine and phenylephrine during anesthesia in horses, increasing doses of dobutamine and phenylephrine were infused to 6 healthy Thoroughbred horses. Anesthesia was induced with xylazine, guaifenesin and thiopental and maintained with sevoflurane at 2.8% of end-tidal concentration in all horses. The horses were positioned in right lateral recumbency and infused 3 increasing doses of dobutamine (0.5, 1.0 and 2.0 µg/kg/min) for 15 min each dose. Following to 30 min of reversal period, 3 increasing doses of phenylephrine (0.25, 0.5 and 1.0 µg/kg/min) were infused. Cardiovascular parameters were measured before and at the end of each 15-min infusion period for each drug. Blood samples were collected every 5 min during phenylephrine infusion period. There were no significant changes in heart rate throughout the infusion period. Both dobutamine and phenylephrine reversed sevoflurane-induced hypotension. Dobutamine increased both mean arterial blood pressure (MAP) and cardiac output (CO) as the result of the increase in stroke volume, whereas phenylephrine increased MAP but decreased CO as the result of the increase in systemic vascular resistance. Plasma phenylephrine concentration increased dose-dependently, and these values at 15, 30 and 45 min were 6.2 ± 1.2, 17.0 ± 4.8 and 37.9 ± 7.3 ng/ml, respectively.

Effects of dobutamine, dopamine, phenylephrine and noradrenaline on systemic haemodynamics and intestinal perfusion in isoflurane anaesthetised horses

“…Heart rate was reduced, most likely as a reflex response to the increased afterload. The concurrent drop in CO and SV is consistent with previous reports on cardiovascular effects of phenylephrine in horses using similar dose ranges to this study [9,10]. The decrease in local microvascular perfusion at all three measurement sites with phenylephrine indicates a redistribution of blood away from the intestinal measurement site due to the a-mediated vasoconstriction.…”

“…The peripheral vasodilation, indicated by a decrease in SVR, combined with an increase in CO and SV positively influenced local blood flow in this experiment. Previous studies in anaesthetised horses , cats and man using comparable doses, showed similar results regarding systemic haemodynamic parameters. In terms of altering local mesenterial blood flow or oxygen delivery, previous studies in hypotensive foals or experimental models of sepsis failed to show a significant influence on the gastrointestinal perfusion, although jejunal mucosal blood flow has been shown to improve after cardiac surgery with dobutamine infused at 2.7 ± 0.1 μg/kg bwt/min .…”

Effects of dobutamine on cardiovascular function and oxygen delivery in standing horses

“…DAP, diastolic arterial blood pressure; MAP, mean arterial blood pressure; SAP, systolic arterial blood pressure right-ventricular dP/dtmax indicating a positive inotropic effect. In contrast, most of the studies in anaesthetized horses showed an increase in SV and or Qt as the main mechanism of dobutamine improving systemic blood pressure (Craig et al, 2007;Dancker et al, 2018;Lee et al, 1998;Ohta et al, 2013;Schauvliege et al, 2008;Swanson et al, 1985;de Vries et al, 2009). These contradictory results could be attributed to the administration of inhalation anaesthetics causing vasodilation and consequently favouring a larger SV.…”

“…Hinchcliff et al (1991) reported an increase in systemic blood pressure without detectable changes in Qt and SV using a considerably lower dose of dobutamine (0.5 µg kg −1 min −1 ) in conscious horses. Conversely, in anaesthetized horses, dobutamine seems to increase systemic blood pressure primarily by improving Qt and SV (Craig, Haskins, & Hildebrand, 2007;Dancker et al, 2018;Lee, Clarke, Alibhai, & Song, 1998;Ohta et al, 2013;Schauvliege et al, 2008;Swanson, Muir, Bednarski, Skarda, & Hubbell, 1985;de Vries, Brearley, & Taylor, 2009).…”

“…Recently, dobutamine has been shown to improve local perfusion of the gastrointestinal tract in horses (Dancker, Hopster, Rohn, & Kästner, 2018). Considering the positive effects on systemic and local perfusion, dobutamine is recommended as first choice to support cardiovascular function in anaesthetized horses (Ohta et al, 2013). Effects of dobutamine in anaesthetized horses have been investigated by different researchers (Gehlen et al, 2006;Hellyer et al, 1998;Loughran, Raisis, Hosgood, Secombe, & Lester, 2017;Schauvliege, Van den Eede, Duchateau, & Gasthuys, 2008;Taylor, 1998).…”