Knowledge
Vet Insight: General Anaesthesia
David Blakey BVetMed CertAVP(EM) MRCVS started playing polo with The Wilton Hunt Pony Club at the age of 10 and went on to both play and groom in South Africa and the U.K, before setting off for The Royal Veterinary College. He graduated in 2010, and currently works at the Three Counties Equine Hospital in Gloucestershire, the practice that looks after the Polo Times string. He deals with everything from miniature Shetlands to performance sport horses, although he does have a particular interest in anesthesia and older horse management. David regularly plays polo at Edgeworth’s Wednesday evening chukkas and once held a 1 goal handicap, but lack of time and money has curtailed his polo habit
Why, and what are the risks?
A catheter is paced into an artery for direct blood pressure monitoring
An increasing number of veterinary procedures can be performed on horses under heavy sedation, such as wound repair, dentistry, stem cell injections into tendons, wind surgeries and even the repair of some fractures. It is aided by the administration of local anaesthetics, either around nerves to block out whole regions (such as the lower limb) or by injecting under the skin to desensitise the immediate area. If it is possible to perform so many procedures under sedation with the horse remaining on its feet, why would you need to perform general anaesthesia? What is General Anaesthesia? General anaesthesia (G.A.) involves giving a patient a combination of drugs so that they become so deeply asleep that their protective reflexes are abolished – a medically induced coma. This is ideal for surgical procedures as the patient is immobile and cannot consciously feel or remember the procedure. There are two types of G.A. – field and hospital. A field anaesthetic is usually used for relatively quick procedures on yard such as a castration. Typically, the horse is heavily sedated and then given another intravenous 28
Polo Times, May 2020
injection containing ketamine which induces G.A. lasting for 20-30 minutes. This is a very safe form of anaesthesia as it is for a short period and the horse is allowed to recover to its feet in a wide, open space. Hospital anaesthetics are used for longer and more complicated surgeries. The horse is “induced” in the same way as a field anaesthetic, but a tube is placed via the mouth into the trachea and the horse connected to breathing circuit. This delivers a mixture of oxygen and an anaesthetic gas (isoflurane or sevoflurane) that maintains the G.A. once the ketamine has worn off. At the end of surgery, the horse is moved to a padded recovery box where it can breathe off the anaesthetic gas, waking up before getting to their feet.
A horse undergoing castration – this gives better access and safety for the vet
Why? Colic surgery is one procedure that requires general anaesthesia, as the horse must be placed on its back so that the surgeons can open up the abdomen to explore its contents to its fullest extent and correct the cause of the pain. Surgical exploration of delicate structure, such as joints, is only really possible under anaesthesia. The patient can be positioned optimally to allow the joint to be fully assessed with an arthroscope (key-hole camera) and the joint flexed and extended to open up different areas of the joint. This is particularly important when trying to find fragments of bone or foreign objects due to a wound. Some horses will not tolerate procedures even after very heavy sedation. For instance, I know of two horses who require general anaesthesia for hock medications as they cannot be prevented from kicking the clinician any other way. Additionally, the risk of sudden movement in some sedated horses presents a danger to the operating team, equipment and the horse itself – a bit like trying to change a tyre if the car might drive away at any moment. www.polotimes.co.uk
Photography courtesy of David Blakey
General Anaesthesia
