ABSTRACT. Seven Thoroughbred horses were castrated under total intravenous anesthesia (TIVA) using propofol and medetomidine. After premedication with medetomidine (5.0 g/kg, intravenously), anesthesia was induced with guaifenesin (100 mg/kg, intravenously) and propofol (3.0 mg/kg, intravenously) and maintained with constant rate infusions of medetomidine (0.05 g/kg/min) and propofol (0.1 mg/kg/min). Quality of induction was judged excellent to good. Three horses showed insufficient anesthesia and received additional anesthetic. Arterial blood pressure changed within an acceptable range in all horses. Decreases in respiratory rate and hypercapnia were observed in all horses. Three horses showed apnea within a short period of time. Recovery from anesthesia was calm and smooth in all horses. The TIVA-regimen used in this study provides clinically effective anesthesia for castration in horses. However, assisted ventilation should be considered to minimize respiratory depression.KEY WORDS: equine, propofol, total intravenous anesthesia.
Anesthetic and cardiorespiratory effects of total intravenous anesthesia (TIVA) technique
using propofol-guaifenesin-medetomidine (PGM) and alfaxalone-guaifenesin-medetomidine
(AGM) were preliminarily evaluated in Thoroughbred horses undergoing castration. Twelve
male Thoroughbred horses were assigned randomly into two groups. After premedication with
intravenous (IV) administrations of medetomidine (5.0 µg/kg) and
butorphanol (0.02 mg/kg), anesthesia was induced with guaifenesin (10 mg/kg IV), followed
by either propofol (2.0 mg/kg IV) (group PGM: n=6) or alfaxalone (1.0 mg/kg IV) (group
AGM: n=6). Surgical anesthesia was maintained for 60 min at a constant infusion of either
propofol (3.0 mg/kg/hr) (group PGM) or alfaxalone (1.5 mg/kg/hr) (group AGM), in
combination with guaifenesin (80 mg/kg/hr) and medetomidine (3.0
µg/kg/hr). Responses to surgical stimuli, cardiorespiratory values, and
induction and recovery characteristics were recorded throughout anesthesia. During
anesthesia induction, one horse paddled in group PGM. All horses from group AGM were
maintained at adequate anesthetic depth for castration. In group PGM, 3 horses showed
increased cremaster muscle tension and one showed slight movement requiring additional IV
propofol to maintain surgical anesthesia. No horse exhibited apnea, although arterial
oxygen tension decreased in group AGM to less than 60 mmHg. Recovery quality was good to
excellent in both groups. In conclusion, TIVA using PGM and AGM infusion was available for
60 min anesthesia in Thoroughbred horses. TIVA techniques using PGM and AGM infusion
provided clinically acceptable general anesthesia with mild cardiorespiratory depression.
However, inspired air should be supplemented with oxygen to prevent hypoxemia during
anesthesia.
To evaluate the bispectral index (BIS) as an indicator of anesthetic depth in Thoroughbred horses, BIS values were measured at multiple stages of sevoflurane anesthesia in five horses anesthetized with guaifenesin and thiopental following premedication with xylazine. There was no significant difference between the BIS values recorded at end-tidal sevoflurane concentrations of 2.8% (median 60 ranging from 47 to 68) and 3.5% (median 71 ranging from 49 to 82) in anesthetized horses. These BIS values during anesthesia were significantly lower (P<0.01) than those in awake horses (median 98 ranging from 98 to 98) or sedated horses (median 92 ranging from 80 to 93). During the recovery phase, the BIS values gradually increased over time but did not significantly increase until the horses showed movement. In conclusion, the BIS value could be useful as an indicator of awakening during the recovery period in horses, as previous reported.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.