This prospective, randomized, blinded study by Hulda Harðardóttir and colleagues in the UK and Iceland compared two doses of ketamine (2.2 mg/kg and 5 mg/kg i.v.) for induction of anesthesia in 77 Icelandic horses undergoing field castration. Prior to induction horses were sedated with xylazine (0.7 mg/kg), butorphanol (25 μg/kg) and acepromazine (50 μg/kg) i.v. and sedation quality was assessed 5 minutes later. Horses were randomly allocated one of the two ketamine doses and induced with intravenous ketamine and diazepam (30 μg/kg). Induction quality, surgical conditions and recovery were assessed using subjective and objective measures.
Horses that received the higher dose of ketamine became relaxed more rapidly after induction, and surgical conditions were better; however, recovery quality was subjectively worse. Five horses that received the lower dose of ketamine required additional ketamine doses during anaesthesia compared to only two that received the higher dose.
Bottom line: A ketamine dose of 5 mg/kg i.v. may result in better surgical conditions but adversely affects recovery quality for field surgery.
The authors of this study were Harðardóttir, H.; Murison, P.J.; Blissitt, K.; Olason, S.; and Clutton R.E.