The operating theatre should be free from microorganisms and spores and maintained as an aseptic environment. The horse itself is the greatest source of potential contamination of theatre and exogenous microorganisms found on the skin and coat are frequently the most common cause of contamination in a clean surgical wound (McHugh, 2012). Meticulous preparation of the patient is therefore essential and time and care must be taken during this procedure. Horses are big animals and this makes the positioning a complex process, particularly owing to the associated risks such as myopathy and neuropathy. The type of operation will determine the positioning; however, the patient's health must always be kept at the forefront of the nurse's mind.
There is always a lot to do during the pre-operative preparation of a horse and organisation is the key. In order to keep the anaesthetic time to a minimum, it is important to do as much preparation as possible prior to induction. The preparation will be determined to a certain extent by the type of operation and the surgeon in charge.
Preparing the horse
In emergency situations, there may not be time for all of the desirable pre-operative preparations. However, for elective procedures, the following should be carried out, although clipping is a matter of preference:
Starving
Horses should to be starved for at least 8 hours prior to surgery. It is normal to withdraw all food at midnight the night before (Corley and Stephen, 2008).
Obtaining the weight
Obtaining an accurate rate is vitally important in order to calculate accurate doses for preoperative medications and anaesthetic induction agents.
Shoe removal
Shoes are removed to protect the horse and the recovery box floor during recovery from the anaesthetic. The feet must then be thoroughly scrubbed clean and, after induction, covered with rectal sleeves prior to winching into theatre, to prevent contamination.
IV catheter placement
The catheter should be placed into the left jugular vein if the horse is to be positioned in dorsal recumbency, or the uppermost vein if the horse is to be positioned in lateral recumbency. An aseptic skin preparation of the catheter site is essential before placement
Grooming or bathing
The horse should be groomed thoroughly to prevent contamination of the theatre. Some horses, especially those with long coats and feathers, may require bathing to facilitate asepsis. The mane should be plaited if long and the tail tied up and covered with a bandage or rectal sleeve.
Rinsing the mouth
Rinsing the horse's mouth is vital to prevent the patient from aspirating food material on placement of the endotracheal tube.
Clipping
A large area around the surgical site should be clipped; as a guide, there should be at least a hand-span width clipped around where the incision is going to be made. A size 40 clipper blade is ideal for a close surgical clip. Care must be taken in order to not damage the skin while clipping, as this may increase the risk of post-operative sepsis (Hendrickson, 2012).
Some say that clipping prior to anaesthesia improves asepsis as loose hairs are shed before surgery, decreasing contamination of the surgical site. Others argue that it increases skin bacterial flora, therefore decreasing asepsis (Hague et al, 1997). One practical advantage is that it does significantly reduce anaesthesia time for the patient. However, the decision about whether to clip pre operatively or not is determined by the surgeon's preference.
Foot preparation
All horses’ feet are thoroughly scrubbed before surgery as there are many areas for bacteria to populate. For surgery involving the foot or a structure close to the foot, scrupulous preparation is essential. Once the shoe has been removed, the foot should be pared and nail holes opened up prior to cleaning (Figure 1). The hoof wall and sole should then be scrubbed with dilute povidone iodine solution (0.1–0.2%). Following this, gauze swabs soaked in a strong povidone iodine solution (10.0%) should be used to pack the foot and cover the hoof wall (McIlwraith et al, 2005). To finish, a foot dressing is applied and covered with an empty drip bag, secured around the cannon with adhesive tape. This provides extra protection as the aim is for the dressing to be left in place for 12–24 hours prior to surgery, to allow the iodine to soak into the hoof wall and sole. Once the horse is positioned for surgery, the dressing is removed.
Handover of the patient
It is important to communicate all necessary information about the patient to the surgical team. The anaesthetist will need to know which pre-operative drugs the patient has been given and how the patient has behaved during the preparation. This may determine whether the patient requires further pre-operative sedation prior to being induced to ensure that the induction process goes as smoothly as possible. The surgical nurses will need to know if any further clipping is required and whether the feet will need further scrubbing once the horse is induced. Both of these factors are usually the result of the patient being too fractious to carry out the task.
Positioning of the horse
The horse will either be placed on the table in dorsal or lateral recumbency depending on the operation being performed, as well as the preferences of the surgeon and anaesthetist. Owing to the sheer weight of horses, the key to success is supporting all parts of the horse's body as well as possible. This can be achieved with the use of limb supports, inflatable cushions, foam wedges and, in some cases, fluid bags, as these help to fill the small gaps that some cushions cannot.
Dorsal recumbency
The horse must be well supported at the shoulders. This will ensure that it is well balanced and lies in a central position on the mattress (Figure 2). When winching the horse into theatre, it is always a good idea to have someone assigned to guiding the withers of the horse into the centre of the bed and positioning the shoulder cushions accordingly, depending on the size of the horse. It is important not to position the horse too far back on the mattress as their gluteal muscles will not be supported well enough. For certain procedures, an example being hind-limb suspensory neurectomy, the horse needs to be positioned as far back as possible in order for the surgeon to have good access (Figure 3). However, there is a fine line between being far back enough and too far back. Therefore, the horse's best interests must always be paramount in these situations.
Once the horse is positioned on the mattress, each leg should be tied to the table to secure its position. These ropes must not be tied tightly — just enough to keep the horse in position and care must be taken to ensure the ropes do not dig into the patient's upper limbs. Finally, the anaesthetist is normally responsible for letting sufficient air out of the mattress, in order to ensure that the horse is not lying on a hard surface for the duration of the operation, resulting in a myopathy. It is important that nurses check that this is done.
Lateral recumbency
The horse may be positioned in either left or right lateral recumbency and the same principles that apply to dorsal recumbency apply here. Firstly, it is most important to have enough people on hand to help position the horse in lateral recumbency. Horses are big, heavy animals and positioning them can prove to be a tricky task. This is particularly the case if the operation being performed is a dorsal spinous process resection, as the patient is required to be positioned at the edge of the mattress for good surgical access. The manpower are often referred to as ‘the knees’ as several people are needed to act as support using their knees while the horse's legs are winched down into position.
Once the horse is safely on the mattress, the next task to perform is pulling the lower forelimb as far forward as possible to release the triceps muscle (Figure 4). This ensures that the triceps is as free as possible from the weight of the uppermost leg, as this could result in a myopathy (Dugdale, 2010).
All of the limbs must be well supported. The lower limbs should sit in a natural position with a padded cushion underneath and the uppermost limbs should either be supported by using a leg stand or an inflatable cushion that sits between the horse's legs. As with a horse in dorsal recumbency, each leg should be tied down to the table to secure its position and prevent movement. Particular care must also be paid to the horse's head and neck; they should be well supported by the mattress and not forced into an unnatural position (Lin, 2006). Finally, sufficient air should be let out of the mattress to prevent the horse from lying on a hard surface.
Preparation on the table
The following steps need to be considered once the horse is on the table:
Conclusion
The key to the success of preparing and positioning a horse for surgery is organisation. Team work goes hand in hand with organisation as does training all staff involved to a high standard. Without the meticulous preparation and attention to the finest detail when positioning, the prognosis for the patient following surgery may be affected due to an increased risk of infection and complications. When anaesthetising a horse, the role of the nurse is integral. There is a quote by James Baker, that all nurses should remember: ‘Prior preparation prevents poor performance’.