A comparison of two ketamine doses for field anaesthesia in horses undergoing castration

Abstract

Summary Background Ketamine at 2.2 mg/kg given i.v. is often used to induce anaesthesia for surgical procedures in horses under field conditions. Commonly, additional doses are needed to complete the surgery. We hypothesised that surgical conditions would be improved when 5 mg/kg of ketamine was used to induce anaesthesia, while induction and recovery qualities would not differ from those when 2.2 mg/kg ketamine was used. Objective To compare the anaesthetic effects of two ketamine doses (5 and 2.2 mg/kg) during field anaesthesia for castration of horses. Study design Prospective, randomised, blinded, clinical study. Method Seventy‐seven client‐owned Icelandic horses presented for castration under field conditions were studied. Pre‐anaesthetic medication was xylazine (0.7 mg/kg) butorphanol (25 μg/kg) and acepromazine (50 μg/kg) injected i.v. Anaesthesia was induced with either 2.2 mg/kg (K2.2) or 5 mg/kg (K5) i.v. of ketamine mixed with diazepam (30 μg/kg). The quality of induction, surgical conditions and recovery were compared using subjective and objective measures, and the number of additional ketamine doses recorded. Results Ketamine 5 mg/kg provided better surgical conditions and a more rapid induction. Recovery quality was subjectively better in K2.2. Five horses in K2.2 and two in K5 required additional ketamine doses. Main limitations While the pre‐anaesthetic sedation and benzodiazepine doses were consistent among horses, the level of sedation and muscle relaxation achieved differed. Conclusion A ketamine dose of 5 mg/kg can be used to improve the quality of field anaesthesia for castration in Icelandic horses. Although recovery quality is subjectively better when using 2.2 mg/kg, no adverse events were observed during recovery with either dose The Summary is available in Portuguese – see

Early castration in foals: Consequences on physical and behavioural development

“…After a catheter was placed in the jugular vein and warm saline infusion (sodium chloride solution 0.9%, 5 ml/min, Virbac) was started, the following I.V. injections were given at 5‐min intervals: (i) diazepam for neonates (Valium, 0.08 mg/kg bwt, Laboratoire Roche) for sedation and muscular relaxation (in the case of excessive foal agitation, the dose of Valium was increased) 7 ; (ii) romifidine for yearlings (Sedivet, 0.05 mg/kg bwt, Boehringer Ingelheim) for sedation; (iii) butorphanol (Dolorex, 0.015 mg/kg bwt for neonates, 0.02 mg/kg bwt for yearlings, Intervet) for analgesia 8 (this injection was repeated immediately after the operation) 9 and (iv) ketamine (Imalgene 1000, 3‐5 mg/kg bwt for neonates, 2.2 mg/kg bwt for yearlings, Merial SAS) for the induction of anaesthesia 10 …”

Recovery of horses from general anaesthesia: A systematic review (2000–2020) of the influence of anaesthetic protocol on recovery quality

“…Excitation and ataxia were common features of recovery from anaesthesia in horses administered high doses of ketamine (6.6 mg/kg) 139 . Elsewhere, QR was subjectively better when lower doses of ketamine (2.2 vs 5 mg/kg IV) combined with diazepam (0.03 mg/kg IV) were administered 31 . The administration of S‐ketamine (2.5 mg/kg IV) for induction of anaesthesia in horses did not offer any advantages in terms of QR 33 .…”

Immobilisation with intramuscular ketamine as part of the anaesthetic protocol in three companion horses

“…Eighty minutes may be considered a long recovery time which the authors think could have been attributed to the possible ketamine overdose and exhaustion due to maximal exercise intensity followed by a stressful event. Recovery quality was reported to be subjectively better when using low doses (2.2 mg/kg) compared to high doses (5 mg/kg) in a published study 33 . Weight estimation methods in adult horses have been previously described in the veterinary literature and an established formula has been developed; weight (kg) = (heartgirth2 × body length) / (11.880 cm 3 ), 34 although in the cases described visual estimation was the method used and measurement would have been impossible to perform.…”

“…Recovery quality was reported to be subjectively better when using low doses (2.2 mg/kg) compared to high doses (5 mg/kg) in a published study. 33 Weight estimation methods in adult horses have been previously described in the veterinary literature and an established formula has been developed; weight (kg) = (heart-girth2 × body length) / (11.880 cm 3 ), 34 although in the cases described visual estimation was the method used and measurement would have been impossible to perform. Acepromazine (0.77 mg/kg) via the oral route was administered as part of premedication in Case 1 with no significant effects.…”