11 May 2009
William Lewis
Job Title
William Lewis shares his protocol for spaying rabbits – a technique he has refined over many years, and one that he believes is reliable and repeatable
THE rabbit spay is now regarded as a routine operation for veterinarians, yet few colleges actually teach the theory or practice, leaving young vets to discover their own method of performing this common procedure.
In my view, few texts describe the operation adequately, with many leaving out some vital steps to performing it quickly, safely and easily. In this article I will suggest a protocol that provides simple and safe anaesthesia with adequate pain relief, a small wound, easy location of the uterus, simple exteriorisation of the ovary, rapid recovery from anaesthesia and minimal postoperative complications.
Rabbits are spayed to prevent unwanted pregnancies, reduce aggression and, most importantly, to prevent the inevitable uterine adenocarcinomas from developing. Spays are routinely performed at five to six months of age and, as with all patients undergoing anaesthesia and surgery, a thorough clinical examination should be performed.
Confirming the sex is vital, as many an attempt has been made to spay a buck rabbit. Special attention should be paid to the respiratory system. Any nasal discharge, flared nostrils when breathing or exaggerated breathing efforts should be noted, as this may affect anaesthesia and the safety of the procedure. Remember that rabbits breathe with their diaphragm and not their ribs, so breaths may not be as visible as in dogs and cats.
All spays I perform involve an intravenous catheter placed in the marginal ear veins. With a little practice, they are very easy to place. The veterinary nurses at our practice routinely place these catheters when patients are admitted for surgery in the morning. The hair is clipped off the lateral aspect of the ear and lidocaine is sprayed on the skin overlying the vein – it seems to provide a local anaesthetic effect and, in my experience, is more rapid in its onset of action than Emla cream.
A 26-gauge winged catheter is inserted into the vein. Because the vein is very superficial and immobile, the catheter is easy to insert. Be careful to choose a part of the vein that is as straight as possible; this allows a good run at advancing the catheter without encountering a corner. The catheter can be glued or taped into place. We glue a wing of the catheter to the pinna and cover it with tape. A cap with an injection port can be placed on the end of the catheter. These are quite heavy, so an alternative is to place the rubber bung from a 1.0ml syringe into the open end of the catheter. A pre-operative dose of analgesia – using meloxicam at 0.3-0.6mg/kg subcutaneously – is administered. This is off licence; therefore, the owner’s consent should be obtained.
Various anaesthetic protocols can be used and, if you have a protocol that works well for you, then stick to it. My current aim is to use as small a dose of intravenous anaesthesia as possible and to intubate the patient.
If we have been successful at placing the IV catheter, I use a cocktail of three drugs, administered intravenously, to induce anaesthesia. Tiny doses are used, so I draw them up individually in an insulin syringe. This way, I can ensure they are accurate, so can administer small doses and top up to effect. I use a combination of medetomidine at 0.1ml/kg (100µg/kg), ketamine at 0.03ml/ kg (3mg/kg) and butorphanol at 0.03ml/kg (0.3mg/kg).
I have drawn up a dosage chart for rabbits of different weights using a spreadsheet, which makes calculating doses quicker (email [email protected] if you would like a copy).
I inject approximately threequarters of the cocktail intravenously and top up to effect. If it is not possible to insert an IV catheter for some reason, the anaesthetic may be injected directly into the marginal ear vein, lateral saphenous vein or cephalic vein. If, for some reason, you cannot access any of these veins, then consider intramuscular combinations of agents. My favourite combination, and one that I have used successfully on many hundreds of rabbits, is xylazine at 5mg/kg and ketamine at 25-30mg/kg. I draw them up in separate syringes and give one injection in each hindlimb. The patient can then be intubated.
If intubation is not successful, I use a mask – ensuring that the nares are included, but never compressed against the front edge of the mask. If xylazine is not available at your practice, consider a combination of medetomidine (0.15-0.25mg/ kg) and ketamine (10-15mg/kg) given subcutaneously. Fentanyl and fluanisone may be used at 0.2-0.5ml intramuscularly and can be reversed with buprenorphine. The patient may then be masked to allow deepening of anaesthesia and intubation. Remember to use lubricant in the eyes as rabbits do not blink under ketamine anaesthesia and the corneas can rapidly dry out, leading to corneal ulceration.
Most rabbits are quite easily intubated using the visual method. There are two important factors: the rabbit needs to be deeply enough anaesthetised, and it needs to be held in the correct position. The assistant should place the rabbit in ventral recumbency and lift the patient up by the head, so that the feet are clear of the table. Once the head is adequately elevated it should be tilted backwards, so the open end of the mouth is pointing towards the ceiling.
I pull the tongue out to the right side of the rabbit’s mouth (the left side as I face the rabbit) with my left hand and insert an auriscope – with the largest head over the base of the tongue – and push it as far back as possible. This way, the opening to the larynx is easily visualised. An assistant then holds the handle of the auriscope, which points to my right side, while I insert a 2.5-3mm tube with an introduction stylet down the auriscope. At this point, the tube should not have the blue connector attached.
The introducer is inserted into the opening of the larynx and the tube is advanced. If there is a reaction from the patient and closing of the larynx then the rabbit will need to be topped up with a little more of the “cocktail” or gas applied with a mask.
Ideally, the tube should go in with no resistance. The tube is advanced through the auriscope, which can then be gently withdrawn. I always pluck a bit of the rabbit’s fur and place it over the end of the tube to ensure the tube is correctly placed in the trachea. The blue connector is then attached and the tube tied in place. As the tubes are very narrow, tape is attached around them and one piece of tube is secured around each ear. This keeps it straight and prevents it kinking or pulling to one side.
The patient is then connected to the anaesthetic machine. Isoflurane in oxygen is used routinely, but alternative products, such as desflurane or sevoflurane, may also be used. At this stage, I usually give a bolus of intravenous fluids slowly. Hartmann’s is adequate – about 5ml for a 2.5kg rabbit. The patient is then placed in dorsal recumbency on a heat mat and prepared for surgery. The hair is clipped from the pubis to the xiphoid bone and the skin is prepared aseptically – taking care to use warm water and not too much surgical spirit to avoid over-cooling the patient.
Most of the texts advise making the incision from the umbilicus to the pubis. However, in my experience, these landmarks are not always easy to find and can result in an incision that is made too large or in the incorrect position; thus, not allowing for easy retrieval of the uterus or, possibly, leading to the caecum or other parts of the GI tract popping out of the wound. My landmark of choice is the last pair of nipples.
I make an incision about 2-3cm long with two-thirds of the incision cranial to a line drawn through the last pair of nipples and one-third caudal. This creates a wound in exactly the correct position for easy retrieval of the uterus (Figure 1). This is my most important tip in this article.
Many rabbits seem to have non-symmetrical nipples and, in these cases, the incision is from the more caudal to the more cranial of the last pair of nipples. The skin is incised and the linea alba identified. The linea is raised using toothed forceps, and a stab incision is made with the sharp edge of the blade pointed to the ceiling (Figure 2). The wound is then elongated in the usual fashion – taking care to elevate the linea to avoid damaging the intestines, caecum or bladder.
The uterus will be found immediately under the incision at this point (Figure 3). There is no need to look for it by inserting instruments, and no gut segments will be visible. The fat around the cervical area of the uterus is grasped and elevated, which raises the double cervix out of the wound (Figures 4 and 5). One of the uterine horns is followed until its cranial end, where it continues as the fallopian tube (Figure 6). The fallopian tube courses ventrally and then curves back upwards to join the ovary (Figure 7). This is another critical stage of the procedure. If the end of the uterine horn is elevated to try to lift up the ovary, the thin mesovarium will tear, resulting in an ovary that drops down into the wound and is difficult to locate. Instead, you should walk your fingers along the length of the fallopian tube until it curves around to the ovary. At this point, the ovary, together with its large pad of fat, should be elevated, and two clamps placed beneath it (Figure 8). A small window is made in the thin mesovarium between this thick pad of fat and the cranial end of the uterine horn (Figure 9). Make sure the loop of fallopian tube is elevated upwards to avoid leaving a section behind (Figure 10). The tissue below the ovary is ligated using vicryl or polydioxanone suture (PDS) and the mesovarium is transected.
The mesovarium is then ligated in a couple of sections until the cervix is reached. There is a large blood vessel on either side of the cervix and this should be ligated. The vagina is clamped as far cranial as possible and a transfixing suture is placed (Figures 11 and 12). The tract is then removed.
My preference for closure of the linea is to use a continuous pattern of vicryl; PDS leaves a large knot, which is easily visible through the thin skin of a rabbit. An intradermal layer of vicryl is then used to close the midline. In fatter rabbits, a row of subcutaneous sutures may also be placed.
The wound is cleaned and then the patient is placed in ventral recumbency. The isoflurane is switched off and atipamizole is administered at 500µg/kg (the same volume as medetomidine administered).
I routinely send rabbits home post-spay with a 10ml bottle of meloxicam to be used at 0.3mg/kg bid for three to five days. Metaclopramide may also be injected and some rabbits are sent home on oral paediatric drops of this at 0.5-1.0mg/kg tid if there is any concern about gut motility. This comes in a handy 15ml bottle, which is enough to last three to four days following most rabbit spays.
The majority of rabbits are fully recumbent within four to 10 minutes using this anaesthetic protocol. Following this procedure allows rabbit spays to be performed quickly and safely with minimal complications.
• Visit www.vetsonline.com for more of our published clinical articles by this author.
Figure 1. The incision position. The rabbit’s head is situated to the right of the picture.
Figure 10. Loop of the fallopian tube running down towards the kidney and then back up to the ovary.
Figure 11. Transfixing the cranial vagina.
Figure 12. Resecting the uterus.
Figure 2. Tenting the muscles up and extending the incision.
Figure 3. Opening the incision reveals the uterus and surrounding fat.
Figure 4 (far left). The uterus, fallopian tube, ovary and ligament are revealed.
Figure 5 (middle). The ovaries are removed and the double cervix is visible.
Figure 6 (left). The uterus, fallopian tube and ovary with surrounding fat.
Figure 7. The uterus is to the left, with the fallopian tube running across and round the ovary and back to it.
Figure 8. Clamp below the ovary on large fat pad.
Figure 9. The mesovarium.
William Lewis
Job Title