Comparison of thiopentone/guaifenesin, ketamine/guaifenesin and ketamine/ midazolam for the induction of horses to be anaesthetised with isoflurane

Abstract

Forty-eight horses subjected to elective surgery were randomly assigned to three groups of 16 horses. After premedication with 0.1 mg/kg acepromazine intramuscularly and 0.6 mg/kg xylazine intravenously, anaesthesia was induced either with 2 g thiopentone in 500 ml of a 10 per cent guaifenesin solution, given intravenously at a dose of 1 ml/kg (group TG), or with 100 mg/kg guaifenesin and 2.2 mg/kg ketamine given intravenously (group KG), or with 0.06 mg/kg midazolam, and 2.2 mg/kg ketamine given intravenously (group KM). Anaesthesia was maintained with isoflurane. The mean (sd) end tidal isoflurane concentration (per cent) needed to maintain a light surgical anaesthesia (stage III, plane 2) was significantly lower in group KM (0.91 [0.03]) than in groups TG (1.11 [0.03]) and KG (1.14 [0.03]). The mean (sd) arterial pressure (mmHg) was significantly lower in group KG (67.4 [2.07]) than in groups TC (75.6 [2.23]) and KM (81.0 [2.16]). There were no significant differences in the logarithm of the heart rate, recovery time or quality of recovery between the three induction groups. However, pronounced ataxia was observed in the horses of group KM, especially after periods of anaesthesia lasting less than 75 minutes.

Anesthetic and Cardiopulmonary Effects of Total Intravenous Anesthesia Using a Midazolam, Ketamine and Medetomidine Drug Combination in Horses

“…The tendency to display ataxia after standing is relatively common in horses pre-medicated with midazolam [5]. Similar observations have been made after short-term anesthesia of horses administered other benzodiazepine combinations, such as tiletamine and zolazepam [19].…”

“…Endotracheal intubation had been maintained without strong swallowing reflex in all horses during MKM infusion. Midazolam is a centrally acting muscular relaxant similar to guaifenesin, however, it produces more potent anesthetic and muscular relaxant effects in horses, compared to guaifenesin [5]. Midazolam might provide the depression of swallowing reflex during MKM-TIVA.…”

“…We observed minimal cardiovascular changes using MKM-TIVA in horses, such as mild decreases in heart rate, cardiac output and cardiac index and mild increases in stroke volume and systemic vascular resistance. Midazolam produces minimum cardiopulmonary effects [16] and minimal decreases in arterial blood pressure in horses [5,12]. Medetomidine produces decreases in heart rate, cardiac output and increase in systemic vascular resistance by activating central and peripheral α 2 -adrenoceptors [16,27].…”

“…The central muscular relaxation produced by guaifenesin can be replaced by benzodiazepines, including diazepam [4], climazolam [1] and midazolam [5,9,12]. Midazolam may be one of the most useful injectable benzodiazepine because it is water-soluble.…”

Anesthetic and Cardiovascular Effects of Balanced Anesthesia Using Constant Rate Infusion of Midazolam-Ketamine-Medetomidine with Inhalation of Oxygen-Sevoflurane (MKM-OS Anesthesia) in Horses

“…However, diazepam is not suitable for infusion because it has a non-water soluble property. Midazolam is a water soluble benzodiazepine that produces similar pharmacologic effects to guaifenesin and diazepam in horses [8]. Therefore, it is expected that the infusion of midazolam, ketamine and medetomidine drug combination will provide similar effects to that of guaifenesin, ketamine and medetomidine drug combination during inhalation anesthesia.…”