Midazolam and ketamine induction before halothane anaesthesia in ponies: cardiorespiratory, endocrine and metabolic changes

Abstract

Six Welsh gelding ponies were premedicated with 0.03 mg/kg of acepromazine intravenously (i.v.) prior to induction of anaesthesia with midazolam at 0.2 mg/kg and ketamine at 2 mg/kg i.v.. Anaesthesia was maintained for 2 h using 1.2% halothane concentration in oxygen. Heart rate, electrocardiograph (ECG), arterial blood pressure, respiratory rate, blood gases, temperature, haematocrit, plasma arginine vasopressin (AVP), dynorphin, beta-endorphin, adrenocorticotropic hormone (ACTH), cortisol, dopamine, noradrenaline, adrenaline, glucose and lactate concentrations were measured before and after premedication, immediately after induction, every 20 min during anaesthesia, and at 20 and 120 min after disconnection. Induction was rapid, excitement-free and good muscle relaxation was observed. There were no changes in heart and respiratory rates. Decrease in temperature, hyperoxia and respiratory acidosis developed during anaesthesia and slight hypotension was observed (minimum value 76 +/- 10 mm Hg at 40 mins). No changes were observed in dynorphin, beta-endorphin, ACTH, catecholamines and glucose. Plasma cortisol concentration increased from 220 +/- 17 basal to 354 +/- 22 nmol/L at 120 min during anaesthesia; plasma AVP concentration increased from 3 +/- 1 basal to 346 +/- 64 pmol/L at 100 min during anaesthesia and plasma lactate concentration increased from 1.22 +/- 0.08 basal to 1.76 +/- 0.13 mmol/L at 80 min during anaesthesia. Recovery was rapid and uneventful with ponies taking 46 +/- 6 min to stand. When midazolam/ketamine was compared with thiopentone or detomidine/ketamine for induction before halothane anaesthesia using an otherwise similar protocol in the same ponies, it caused slightly more respiratory depression, but less hypotension. Additionally, midazolam reduced the hormonal stress response commonly observed during halothane anaesthesia and appears to have a good potential for use in horses.

Evaluation of the use of midazolam as a co‐induction agent with ketamine for anaesthesia in sedated ponies undergoing field castration

“…Midazolam has been shown to act synergistically with other induction agents [20] and is reported to reduce the induction dose of propofol in both dogs and cats [21,22]. Reduced respiratory rates associated with midazolam have been previously reported in horses and rabbits [8,25] along with increased post-induction apnoea in horses and goats [26,27], although these are not consistent observations [26,28]. Nishimura et al [23] demonstrated that midazolam has no intrinsic analgesic properties but when co-administered with dexmedetomidine it enhanced analgesia in rats [24].…”

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

“…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.…”

The effects of ephedrine on intramuscular blood flow and other cardiopulmonary parameters in halothane-anesthetized ponies

“…Cardiopulmonary parameters in the horse change throughout the course of anesthesia, even when the end tidal concentration of volatile agent is kept constant. The degree and exact timing of these changes depends on a number of factors including the pre‐medicant and anesthetic induction agents employed, and whether or not the animal was breathing spontaneously (Luna et al. 1997, Raisis et al.…”