Extra care needs to be taken for procedures that require the horse to be turned over from one side to the other during surgery, as the lower lung (when laying in lateral recumbency) becomes heavy with fluid and less oxygenated. If the horse is turned over too quickly this heavier lung lobe becomes the upper lung lobe and can compress the lower lobe due to its increased weight and compromise the amount of air that can be inhaled. By holding the horse in dorsal recumbency (on its back) until it takes a good breath, the risk of respiratory compromise is reduced as it allows the heavy lung to become better aerated and reduces the pressure placed on the other lung lobe when turned over.
MINIMISING THE RISKS
Can we eliminate the risk of a horse dying under anaesthesia?
The best we can do is minimise the risks and we can do this by being adequately prepared before the horse is anesthetised. Whilst this may not always be feasible in cases of an emergency, as much preparation that can be done prior to induction to maximise the safety of the horse, should be done. In field anaesthesia, this involves checking the environment in which the horse is to be induced, ensuring adequate room for the horse to lie down in, allowing for movement of the horse during the induction and space to recover and stand without the danger of obstacles to stumble onto or into. Keeping the animal as quiet as possible prior to the anaesthesia is important, as highly strung and excitable horses are much harder to anaesthetise due to the adrenaline circulating through their body. Try and keep noise levels to a minimum during induction and recovery as a horse reacts to a threat with a flight response and sudden loud noises can cause the release of adrenaline resulting in the horse trying to move when not fully anaesthetised.
Except in emergency situations, horses should be well hydrated and not suffering with infections or injuries that compromise their ability to go down or get up readily. If there are injuries that require anaesthesia, then adequate thought should be given into how the horse will be treated and prepared to enable the safest induction and recovery. This may require employing extra people and equipment to help the horse stand on recovery, rather than allowing the horse to get up on its own. Using pulleys and ropes to assist the horse to recovery is fine, provided everything is planned carefully and prepared prior to the horse being induced.
For emergency surgeries where time is crucial, the administration of intravenous fluids can begin while the horse is being prepared for the anaesthesia and can continue throughout the surgery to improve the quality of the anaesthesia. The use of appropriate pain relief pre-surgery and, if necessary, during surgery can also have a positive effect on the quality of the anaesthesia and the recovery. Extremely fit horses often make better candidates for surgery if allowed to “let down” for a couple of days or weeks prior to the anaesthesia — so delaying surgery for a short period to allow this to happen can be beneficial provided the surgery is elective.
In summary, anaesthetising a horse is not something to be taken lightly, but nor is it something to shy away from. It is a vital part of veterinary medicine, and provided adequate care and forethought are given to the procedure before the horse is anaesthetised, the risks can be greatly reduced. Unfortunately, the risks can never be eliminated as even with the best of care and planning by experts there is an inherent risk of death or severe complications, and if these occur it is devastating for everyone. EQ
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