THE PITFALLS OF EQUINE REPRODUCTIVE
PRACTICE- A young practitioners experience
Dr Robin James Moore
Ketamine is not your friend
Ketamine is an NMDA receptor antagonists and a ssociative anaesthetic. It is
very commonly used in equine ambulatory practice, usually for induction and
maintenance of short surgical procedures. These include periosteal strips,
umbilical hernia repair, castrations etc. When used appropriately, ketamine is
highly effective and safe, and contributes to good postoperative analgesia.
Cardiovascular and respiratory depression are minimal.
When used on its own, or inappropriately, however, it can result in
seizures and mania, causing serious injury to horses and handlers. In
large part this is due to the horse’s flight behavior prompting the animal to
stand prematurely (i.e. before anesthetic agents and their depressant
effects on mental, proprioceptive, and motor function have worn off). Limb
fractures have been reported during rough ketamine recoveries. It is
therefore essential to ensure that it is not accidentally given before the
sedative.
The most common scenario is when insufficient premedication is utilized
prior to induction. When ketamine is administered to inadequately sedated
horses, extreme excitation and muscle rigidity may occur, followed by
rough induction and a very unpleasant anaesthetic and recovery.
The following practical guidelines will facilitate smooth induction,
maintenance and recovery of ketamine-based field anaesthetics:
•
Be generous with your α2 sedation and combine it with butorphanol. If the
horse doesn’t look sedated, don’t give the ketamine! Although the horse
becomes unconscious after the induction agent is given, the course of
induction is extremely dependent on the premedication
•
Calculate your induction dose of ketamine accurately: Too little will give
you a rough induction, and too much will give a rough recovery
•
Add an equal volume of diazepam to your ketamine syringe for induction.
This causes excellent muscle relaxation and counteracts the rigidity
typically associated with ketamine. Without the benzodiazepine,
anaesthesia and relaxation are sometimes inadequate and recovery
abrupt. It must be remembered that benzodiazepines alone cause marked
ataxia and muscle weakness, and the ketamine must be given
immediately after / with the diazepam.
•
Relaxation may be slow to develop and the horse should be allowed to
settle for at least 30 seconds after it has gone into lateral recumbency. If
15-‐18
February
2016
East
London
Convention
Centre,
East
London,
South
Africa
70