Total intravenous anaesthesia with ketamine, medetomidine and guaifenesin compared with ketamine, medetomidine and midazolam in young horses anaesthetised for computerised tomography

Abstract

Summary Background There is no information directly comparing midazolam with guaifenesin when used in combination with an alpha‐2 agonist and ketamine to maintain anaesthesia via i.v. infusion in horses. Objectives To compare ketamine–medetomidine–guaifenesin with ketamine–medetomidine–midazolam for total intravenous anaesthesia (TIVA) in young horses anaesthetised for computerised tomography. Study design Prospective, randomised, blinded, crossover trial. Methods Fourteen weanlings received medetomidine 7 μg/kg bwt i.v. and anaesthesia was induced with ketamine 2.2 mg/kg bwt i.v. On two separate occasions horses each received infusions of ketamine 3 mg/kg bwt/h, medetomidine 5 μg/kg bwt/h, guaifenesin 100 mg/kg bwt/h (KMG) or ketamine 3 mg/kg bwt/h, medetomidine 5 μg/kg bwt/h, midazolam 0.1 mg/kg bwt/h (KMM) for 50 min. Cardiorespiratory variables and anaesthetic depth were assessed every 5–10 min. Recovery times after the infusions ceased were recorded and recovery quality was assessed using a composite score system (CSS), simple descriptive scale (SDS) and visual analogue scale (VAS). Multivariable models were used to generate mean recovery scores for each treatment and each recovery score system and provide P‐values comparing treatment groups. Results Anaesthesia was uneventful with no difference in additional anaesthetic requirements and little clinically relevant differences in cardiopulmonary variables between groups. All horses recovered without incident with no significant difference in recovery times. Quality of the anaesthetic recovery was significantly better for the KMM group compared with the KMG group using the CSS (P<0.001), SDS (P<0.001) and VAS (P<0.001). Main limitations No surgical stimulus was applied and study animals may not represent general horse population. Conclusion Midazolam is a suitable alternative to guaifenesin when co‐infused with ketamine and medetomidine for anaesthesia in young horses undergoing noninvasive procedures. Both infusions produce a clinically comparable quality of anaesthesia; however, recovery from anaesthesia is of a better quality following an infusion of ketamine–medetomidine–midazolam.

Effect of Intramuscular Medetomidine Administration on Tear Flow in Rats

“…In addition to medetomidine, other α 2 -adrenoceptor agonists such as detomidine [9][10][11], dexmedetomidine [1,[12][13][14], xylazine [4,7,9,14,15], and romifidine [9,10,[16][17][18][19][20] are also used clinically in many domestic species. Furthermore, some α 2 -adrenoceptor agonists, including medetomidine, are administered not only alone, but also in combination with other drugs, such as opioids, benzodiazepine, phenothiazine, and ketamine [3,5,6,8,[21][22][23][24][25][26][27]. Although medetomidine and the other α 2 -adrenoceptor agonists used alone or in combination with other drugs have potent sedative or analgesic effects, they have been reported to significantly decrease tear flow in dogs [28][29][30][31][32], cats [33,34], horses [35,36], and pigs [37].…”

Recovery after General Anaesthesia in Adult Horses: A Structured Summary of the Literature

“…Benzodiazepines could be used as central muscle relaxants as well. Midazolam instead of GGE might have a dose-dependent influence on recovery, and therefore, an antagonist may be considered [171,176,201,206,211].…”

Total Intravenous Anaesthesia with Ketamine, Medetomidine and Midazolam as Part of a Balanced Anaesthesia Technique in Horses Undergoing Castration

“…This research group recently compared an infusion of ketamine, medetomidine and midazolam with an infusion of ketamine, medetomidine and guaifenesin to maintain anaesthesia for 50 min in 14 young horses undergoing computerised tomography (CT) in a randomised, blinded, cross over study [ 9 ]. Both infusions produced a clinically comparable quality of anaesthesia, however, recovery from anaesthesia was of a better quality following the infusion of ketamine, medetomidine and midazolam [ 9 ].…”

“…This research group recently compared an infusion of ketamine, medetomidine and midazolam with an infusion of ketamine, medetomidine and guaifenesin to maintain anaesthesia for 50 min in 14 young horses undergoing computerised tomography (CT) in a randomised, blinded, cross over study [ 9 ]. Both infusions produced a clinically comparable quality of anaesthesia, however, recovery from anaesthesia was of a better quality following the infusion of ketamine, medetomidine and midazolam [ 9 ]. While both infusions appeared equipotent, a major limitation of this study was that horses were not subjected to a nociceptive stimulus, as would be common in clinical practice, and there are currently no reported studies investigating this infusion for surgical procedures in horses at these infusion rates.…”

“…This balanced anaesthetic approach also enables a reduction in individual anaesthetic agent doses, minimising their associated undesirable side effects [ 11 ]. In addition to the anaesthetic technique previously reported [ 9 ], to provide clinical applicability for equine veterinarians, this study included additional premedication and co-induction drugs and intra-testicular local anaesthetic, as commonly used in the field when performing such castration procedures. We hypothesised that an infusion of ketamine, medetomidine and midazolam, when used as part of a balanced anaesthetic technique at the current infusion rates, would be suitable to maintain anaesthesia in colts for routine surgical castration.…”