Anaesthesia provides a temporary loss of sensation and/or awareness, enabling us to safely perform a variety of different medical and surgical procedures. Nowadays many of these procedures can be carried out under standing sedation, often combined with local anaesthesia to provide loss of sensation to a given area.
There are, however, certain surgical and imaging situations for which general anaesthesia is essential.
Routine general anaesthesia requires careful planning. The horse must be fully assessed to ensure good health before surgery - if any abnormalities are detected on examination, they will be investigated to ensure they do not increase the anaesthetic risk.
During preparation for surgery, the horse will be weighed (allowing drugs to be given at the appropriate dose), brushed off, shoes will be removed and an intravenous catheter is placed into the neck to facilitate the administration of drugs and fluids.
First, a ‘premedication’ will be given. This will most likely include antibiotics, pain relief and a sedative. The horse will then be moved into a padded ‘knock-down’ room for induction of anaesthesia.
General anaesthesia is achieved by injecting medication into the pre-placed catheter and allowing the horse to fall to the floor. Often this ‘fall’ will be assisted by the surgery team (one person at the head, one person at the shoulder and a couple behind, to encourage the horse down bottom first to avoid any injuries) however it will vary depending on the size and temperament of the horse.
Once on the ground, an endotracheal tube is placed through the mouth and into the lungs, and the horse is hoisted onto a specially designed, padded table. Careful positioning on the table is essential to ensure that there is no uneven pressure applied to the horse’s muscles.
We take a ‘multi-modal’ approach to anaesthesia, meaning that we use a number of different drugs, given by a variety of methods to achieve the smoothest anaesthetic possible. We will connect the endotracheal tube to a machine which allows oxygen and anaesthetic gas to be inhaled and this machine is also connected to a mechanical ventilator which will support respiration whilst the horse is asleep. Other drugs and supportive fluids are given through the intravenous catheter. This means that each drug is given at the lowest dose possible and easily monitored, making the anesthetic as safe as possible.
Careful monitoring is essential, this will be done both manually - checking the respiratory and heart rate at all times, but we will also monitor many other parameters including the horse’s ECG, oxygenation levels and blood pressure. Blood pressure monitoring is achieved by inserting a small catheter into one of the facial arteries (the face is used as it is logistically the closest to the anesthetist). This provides invaluable information about the stability and depth of anaesthesia, this may be why your horse comes home with some clipped patches on their face after surgery.
Once the procedure is complete, the horse is moved, on the hoist, from theatre and into a recovery box - another padded room. Recovery can be challenging, and therefore we attempt to keep the horse lying down until they have regained sufficient levels of co-ordination and are able to stand relatively easily. The room is kept dark and quiet, and it is likely that additional sedation will be given. Again, they are closely monitored until they are standing safely, when they will be moved back to their stable.