ANAESTHESIA AND POST-OPERATIVE CARE

Transcription

1 1 Anaesthesia Anaesthetic risk Rabbits have a reputation for dying under general anaesthesia, risk, which makes owners and vets apprehensive about anaesthetising them. While it is true that the mortality rate during or after anaesthesia is higher in rabbits than in dogs and cats, it does not mean that the risk is high. Many rabbits have repeated anaesthetics for dentistry without any obvious detrimental effects. When a rabbit does die during or after a general anaesthetic, it is usually the anaesthetic agent or protocol that is blamed, yet this is unlikely because modern anaesthetic agents are inherently safe. Instead, it is the anatomy of the airway, the rabbit's susceptibility to stress and their ability to hide signs of serious disease that cause problems. Pre-anaesthetic examination Conditions that compromise respiration or circulation can be missed easily in rabbits, unless they are so severe that dyspnoea is obvious. Rabbits are not taken for walks so poor exercise tolerance is not evident. Coughing is not a feature of serious lung or cardiac disease. Instead, there is usually an increase in respiratory rate or effort, which may be subtle and could be due to other causes, such as stress or ketoacidosis. Watching a rabbit breathing for a few moments is as important as auscultation. It can be revealing, although a thick coat can mask an increase in respiratory rate. Respiratory noise is an indicator of respiratory disease although it is very difficult to differentiate between upper respiratory tract noise and lower respiratory tract noise. Listening carefully without the stethoscope or placing the stethoscope over the trachea or nose sometimes helps to locate the source of respiratory sounds. Sneezing is a feature of upper respiratory tract disease, which is significant because rabbits breathe through their noses and only mouth breath if their nasal passages are almost completely blocked. Rhinitis, nasal foreign bodies or tumours increase the risk of hypoxia and cleaning the nostrils and pre-oxygenation prior to anaesthesia can be helpful in rabbits with a nasal discharge. Auscultation of the heart is recommended even though cardiomyopathy or mineralisation of the aorta, rather than valvular lesions, are the heart conditions that rabbit suffer from. Heart murmurs are rarely heard but are always significant. Other signs of heart disease include periodic bilateral exophthalmos, dysrhythmias and pleural effusion. Bilateral exophthalmos is a sign that can easily be checked during pre-anaesthetic assessment. It is seen in conditions that compromise venous return to the heart and result in engorgement of the large orbital venous sinus. The exophthalmos becomes more marked if the body is raised higher than the head. It is often associated with thymic masses but is also seen in some cases of congestive heart failure. Underlying renal disease can be difficult to rule in or rule out pre-operatively. Blood urea and creatinine values are not reliable indicators and polydypsia and polyuria can go unnoticed. Renal disease is manifested by weight loss but appetite can remain good despite major renal pathology. Radiology can be helpful as soft tissue mineralization, osteosclerosis or nephrolithiasis can be seen radiographically. Stress At the time of anaesthesia, many rabbits are already stressed. Their routine has been disrupted by a journey to the vets and travelling in itself can be stressful. Diseases such as dental disease or urine scalding are painful and therefore stressful. Once the rabbit is at the surgery, unfamiliar surroundings, transport, rough handling and the proximity of potential predators, including humans, can add to stress levels.

2 2 As well as its effects on gut motility and renal function, stress can cause catecholamine release that increases the risk of cardiac arrhythmias, especially if the animal is hypoxic. Providing food and a quiet, secluded environment away from barking dogs can help to reduce stress levels. Gentle restraint is also helpful. Fluid therapy It is important to make sure that rabbits have eaten and drunk prior to anaesthesia. If there is any doubt about whether the rabbit has eaten or not, syringe feeding is indicated. Intravenous fluid therapy is not essential for healthy rabbits undergoing anaesthesia although but many practitioners prefer to place an intravenous catheter as part of their anaesthetic protocol and routinely give intravenous fluids to all anaesthetised patients, including rabbits. This is a matter of personal preference. Intravenous fluids are indicated for shocked or hypovolaemic rabbits although they must be given slowly at the outset because of the risk of sudden cardiac overload. Overperfusion is also a risk if excessive amounts of fluid are given too quickly. Flow rates of 5-10mls/kg/hour are sufficient. Anaesthetic equipment Accurate scales. Knowing the correct weight of the rabbit means that accurate doses of all medications are given. Oxygen. Even if anaesthesia is induced with injectable agents and no inhalational agent is used, the availability of oxygen is essential, as there is always a risk of hypoxia. A clear face mask that fits tightly around the nose. This can be used for pre-oxygenation, induction, maintenance and, in an emergency, assisted ventilation. A range of endotracheal tubes and water soluble lubricating jelly. V-gel tubes can be very useful Local anaesthetic. Application of local anaesthetic, such as lignocaine, to the larynx aids intubation. A circuit with low dead space and low resistance. Circuits such as a T-piece are essential for rabbits. They can be used for intermittent positive pressure ventilation if necessary. Good lighting and some crocodile forceps. Some rabbits will chew newspaper or eat caecotrophs just before anaesthesia and these may need to be removed from the oral cavity rapidly. Rodent gag, cheek dilators and curved scissors (or dental spatula). Not only are curved scissors useful for clipping off hair over veins but when closed they are the ideal instrument for moving the tongue out of place during examination of the oral cavity, which may need to be done quickly if there is an obstruction to the airway A set of dedicated clippers (or blades) for rabbits. This will reduce anaesthetic time. Cold hardened, tungsten-coated blades are recommended. A heat pad or other suitable heat source. Rabbits easily become hypothermic during and after anaesthesia. Minimising heat loss throughout the anaesthetic period by placing rabbits on towels or heat pads may be necessary. The rectal temperature of rabbits should be between 38.5 ο ο C. EMLA cream. If an intravenous cannula is to be placed in most or all patients, clipping the fur off and applying EMLA cream over the marginal ear vein is useful. It can be done on admission. The worst that can happen is that the area is anaesthetised unnecessarily and the rabbit has the minor discomfort of a bandage (or finger from a disposable glove) on its ear for an hour or two.

3 3 Nitrous oxide. The use of nitrous oxide is controversial, especially in herbivores. It can contribute to hypoxia and diffuse into closed-gas spaces but nitrous oxide appears to be useful and effective in rabbits. It is analgesic, has minimal effect on cardiovascular and respiratory function and reduces the amount of the volatile agent. In rabbits, a 50/50 percent mixture of nitrous oxide and oxygen aids smooth induction and helps to achieve balanced anaesthesia. Once a satisfactory plane of anaesthesia is reached, the nitrous oxide can be switched off. If nitrous oxide is used, when the surgery ends 100% oxygen is administered for at least ten minutes to prevent hypoxia. Endoscope. A small (preferably 1.2 mm) rigid endoscope in a sheath can be extremely useful in rabbits. It allows visualization of the pharynx and larynx and facilitates intubation in rabbits that are hard to intubate or have upper airway problems. A small endoscope is also invaluable for rhinoscopy, otoscopy and other endoscopic procedures in rabbits. Monitoring equipment. Pulse oximeters, capnographs and blood pressure monitors, oesophageal stethoscopes are all very useful, especially for larger rabbits in which probes can be placed easily. In small rabbits, there can be problems with detecting a signal or a pulse. The pharynx may be too small to accommodate an oesophageal stethoscope and an endotracheal tube. The time spent adjusting equipment diverts attention away from the animal and increases the anaesthetic period, which increases anaesthetic risk. Compromises are often required. The use of monitoring equipment is a matter of personal preference. Tips for the anaesthetist. Keep anaesthetic time as short as possible. Although the nursing staff cannot make a surgical procedure faster, they can help reduce anaesthetic time by making sure the correct equipment is well maintained and to hand and that the rabbit is anaesthetised sufficiently for surgery. Trust the anaesthetic agents. It is extremely difficult, or even impossible, to kill a rabbit with modern inhalation agents, such as isoflurane. Respiratory arrest occurs before cardiac arrest so the rabbit will stop breathing and stop inhaling the gas before the heart stops. Injectable agents are safe if they are given in the correct dose so weigh the rabbit accurately in order to calculate dosages. A ready reckoner that has calculated doses for all the common drugs that are used for treating rabbits, including anaesthetic agents, is extremely useful. The drugs are safe and there is a wide range of dose rates for most of them. Be confident and keep the rabbit asleep. In general, more problems result from a rabbit that is too lightly anaesthetised rather than too deeply. However, the instinctive reaction of an anaesthetist who is not confident is to switch off the anaesthetic gases or at least reduce the concentration. This can make matters worse because a lightly anaesthetised rabbit is more likely to breath-hold or move in response to surgery. Watch the rabbit, not the surgery. Do whatever you need to maintain concentration. Anaesthetic charts can be helpful to maintain the anaesthetist s concentration. Keeping a hand gently across the chest allows the apex beat to be monitored. Provide analgesia. Pain is stimulating and decreases the plane of anaesthesia. Prevent hypoxia. Rabbits are prone to hypoxia. They do not cough or retch in response to pharyngeal obstruction and their lungs are small in comparison with dogs and cats. Their tidal volume is only 4-6mls/kg. Hypoxia can develop easily as a result of breath holding, occlusion of the airway, upper respiratory disease, increased weight of viscera on diaphragm, pre-existing lung disease or firm restraint around chest.

4 4 The trachea is narrow and short, so small endotracheal tubes are required, which kink or dislodge easily, especially during dental procedures or surgery around the head. These risks can be reduced by making sure that the rabbit is well oxygenated and that endotracheal tubes are correctly placed throughout the surgery. Remember resuscitation works if respiratory or cardiac arrest is recognised promptly. Drugs and protocols There is a multitude of protocols for rabbit anaesthesia, which is constantly changing as new products come on to the market. Different combinations of medetomidine, ketamine, benzodiazepines, Alfaxan, propofol, butorphanol, buprenorphine, tramadol, acepromazine, fentanyl, morphine and xylazine at various doses are recommended for sedation and/or general anaesthesia in various texts and everyone has their favourite and least favourite. Anaesthetic induction Masking down with no premedication. This can work well with sevoflurane because it is odourless. If isoflurane is used, it smells unpleasant and the rabbit is likely to breath-hold or struggle. Fast recovery is an advantage. Struggling can be a problem with this method of induction. Wrapping the rabbit in a towel can help but makes it hard to observe respiration. Masking down with premedication. This was my preferred method of inducing rabbit anaesthesia. Although it can be time consuming, it has the advantages of good control over anaesthetic depth, a smooth quiet induction and rapid recovery. The rabbits are premedicated with a combination of 0.05mls/kg (50µg/Kg) of medetomidine, 0.05mls/kg (5mg/kg) ketamine and 0.05mls/kg (0.5mg/kg) butorphanol mixed in the same syringe and given subcutaneously. Tramadol (0.1mls/kg) is given intravenously or subcutaneously preoperatively to all rabbits that are undergoing surgery that is likely to be painful. Once the rabbit is sedated (usually after 5-15 minutes), it is placed on the table and a tightly fitting mask is used to administer oxygen for a few minutes. The rabbit is held gently, without a towel, so that its respiration can be seen clearly. Nitrous oxide can be introduced before the anaesthetic agent. After a few more minutes, isoflurane is introduced, initially at 0.5% and then slowly increasing it over 5 minutes to 2.5-3% by which time the rabbit is in a surgical plane of anaesthesia and ready for endotracheal intubation or insertion of a V-gel device. Maintaining anaesthesia with a facemask is also an option. Intravenous induction with alfaxone gives a faster induction, although it can be difficult to get the dose just right for intubation. The rabbit needs to be breathing but immobile. Apnoea can occur at higher doses or if the injection is given quickly. The amount of induction agent depends whether the rabbit has been pre-medicated or not. The recommended dose rate of alfaxalone 0.5-2mg/kg. Endotracheal intubation Endotracheal intubation is safe in rabbits and does not traumatise the larynx if it is done carefully. The ability to intubate rabbits makes a huge difference to anaesthetic safety because it maintains a clear airway and prevents hypoxia. It makes dentistry and abscess surgery much, much easier. Careful examination of the mouth prior to intubation is recommended, especially in rabbits with a respiratory noise or those that have been chewing their bedding material prior to anaesthesia. Usually the mouth is empty but any material that might be pushed into the trachea by the endotracheal tube needs to be removed.

5 5 Endotracheal tubes Uncuffed, clear tubes are the most satisfactory endotracheal tubes. A 2mm tube is the smallest size that is available and is suitable for rabbits weighing 1-2kg although it can also be used for larger rabbits if a bigger tube will not enter the trachea easily. Most pet rabbits weigh about 2.5kg and take a 2.5mm tube. A 3mm tube can be used in larger rabbits (3-3.5kg) with a 3.5 mm tube for the larger ones. Clear tubes are useful because condensation caused by exhalation can be seen within the tube. Lubricating the endotracheal tube with water soluble lubricating jelly prior to insertion aids atraumatic intubation. Condensation in the tube or from the end of the tube on the surface of the operating table confirms correct positioning. Blind intubation, without visualisation of the larynx, is satisfactory in the majority of cases although a rabbit that is difficult to intubate can be encountered. For blind intubation, the rabbit is placed in sternal recumbency with its neck extended and a few drops of lidocaine (without adrenaline) is instilled into the back of the mouth so it trickles over the tongue and on to the larynx. After a few moments, a lubricated tube is inserted through the mouth and into the pharynx. An idea of the position of the end of the tube can be gained by putting an ear to the end of the tube and listening for breath sounds while watching the rabbit's respiratory movements. Once breath sounds are heard, the tube is slowly advanced during each inspiration. The breath sounds become louder until the tip is situated at the entrance of the larynx. At this point, the breath sounds are at their loudest. Rotating the tube at this point may move the epiglottis and allow the tube to enter the larynx. Also, dropping 3-4 drops into the endotracheal tube when it is positioned above the larynx delivers local anaesthetic directly onto and into the larynx, which can help intubation. If breath sounds are lost when the tube is advanced further, then it has almost certainly passed into the oesophagus. Resistance is felt if this is the case. If the tube passes into the oesophagus, it needs to be withdrawn until breath sounds are heard again. When endotracheal intubation is successful and the tube goes through the rima glottidis into the larynx, the rabbit will usually cough and breath sounds can still be heard through the tube. If the first attempt is unsuccessful, then the procedure can be repeated using a smaller tube. Direct visualisation of the larynx with an endoscope is by far the easiest, quickest and safest way to intubate rabbits but requires an expensive, fragile piece of equipment. A small (1-2mm) sheathed endoscope is inserted into the endotracheal tube before locating the larynx endoscopically. Once, the scope and tube are in the trachea, the scope is withdrawn. Suitable endoscopes for inserting into endotracheal tubes are available from MSD-VET. If a small endoscope is not available, a 2-3mm scope can be used to visualise the larynx while an endotracheal is inserted into it. V-gel devices V-gel tubes are supraglottid devices or laryngeal masks. They are used in human anaesthesia. They prevent laryngeal trauma. The device has a non-inflatable soft-gel cuff to create a seal over the glottis and also incorporates an oesophageal seal to prevent aspiration of any gastric reflux. Unlike endotracheal tubes, V-gel devices are easy to place. They seal the larynx effectively. The devices are quite expensive to buy and come in range comes in six sizes, with the smallest designed to fit rabbits down to 600g in body weight. Their disadvantages are that they occupy too much of the oral cavity to be used during dentistry and they can become dislodged during anaesthesia. The use of capnography to make sure they are still in place is recommended by the manufacturers.

6 6 Monitoring anaesthesia Ideally, monitoring equipment should be used for every anaesthetic but, in general practice, the correct equipment for rabbits may not be available or may be difficult and time consuming to set up. It is possible to monitor anaesthesia effectively without additional equipment but it does require someone to concentrate on the rabbit at all times. This is a reliable method of monitoring anaesthesia. Monitoring parameters The colour of the mucous membranes can be assessed by looking at the nose, lips or tongue. Feeling the temperature of the ears or feet is a guide to body temperature although a thermometer or probe can be set up. The rate, depth and pattern of respiration are useful indicators of depth of anaesthesia. Respiratory depression can be considered to be severe at less than 4 breaths per minute. The heartbeat can be felt by placing a finger on either side of the chest. Typical heart rates are bpm, although rates of bpm can occur in rabbits that have received medetomidine. A sudden fall in heart rate is significant and can precede respiratory or cardiac arrest. The absence of an ear pinch reflex and loss of jaw tone are reliable indicators of surgical anaesthesia. The toe pinch, leg withdrawal reflex is more reliable using the hind rather than the fore feet. As in other species, the eye gives a guide to the depth of anaesthesia although the reflexes are slightly different. The palpebral reflex cannot be relied upon to give an accurate assessment of the depth of anaesthesia although rabbits that are blinking are light and those with no corneal reflex or palpebral reflex are deep. An eye that is up and wide open denotes a dangerous depth of anaesthesia especially if it is bulging slightly. This is due to engorgement of the venous sinus, which occurs in heart failure. The pupillary reflex can be hard to assess and is affected by induction agents, such as ketamine. If respiratory or cardiac arrest occurs, prompt resuscitation will often be effective, but only if the person monitoring the anaesthetic has recognised that there is a problem as soon as it happens. Resuscitation Protocol Rabbits seem to go into respiratory arrest more readily than dogs or cats. If someone is watching and notices that the patient is not breathing, the rabbit can often be resuscitated in the following way Check the plane of anaesthesia - respiratory arrest may be due to breath holding because the rabbit is light. In these situations, the rabbit needs more anaesthetic drugs, not less, even though it is instinctive to switch the anaesthetic gas off. Check the airway is clear. The neck may need to be stretched out. There may be a problem with the equipment, such as twisting the exit from the bag or a surgeon gripping the rabbit tightly around the neck or leaning on the chest. Make sure patient is oxygenated. IPPV can be used if the rabbit is intubated or use the face-mask if the patient is not intubated. If the mask fits tightly it is still possible to inflate the lungs by filling the reservoir bag with oxygen and compressing it. The lungs can be inflated in rabbits that have a V-gel in place.

7 7 Gently compress the chest between finger and thumb to move air in and out of the lungs and stimulate respiration. The chest can be compressed at a rate of once per second. If cardiac arrest has occurred, use external cardiac massage over the heart at rate of approximately times per minute. Find the emergency drugs. Some people draw up doses in advance. We have a box handy, with all the drugs that might be needed as well as a dosage chart. Recovery from anaesthesia Careful observation is necessary for rabbits recovering from anaesthesia. If their airway is occluded, e.g. by food, blood or pus in the larynx, the rabbit s response is not to cough or show respiratory effort. Instead, they stop breathing and die. Positioning them so they have a clear airway is beneficial. A low body temperature can prolong recovery but hyperthermia can also be a risk, so discretion is required about which rabbits require heat pads and which do not. Comfort, a quiet recovery area, good food, water and analgesia are essential for all rabbits that have undergone surgery. Analgesia Non-steroidal preparations (NSAIDs) NSAIDS, such as carprofen (3mg/kg) or meloxicam (0.3mg/kg) are useful in rabbits. They can be given orally, post-operatively and can be used in conjunction with opioids, such as fentanyl or buprenorphine (0.03mg/kg). NSAIDS appear to be safe in rabbits and have not been linked with gastric ulceration. Their benefits outweigh any risk although it is prudent to give them at the end of surgery rather than the outset. It is important to make sure that subcutaneous injectable products are administered properly beneath the skin and area massaged to dispel the product. Injection reactions are common and injectable NSAIDS are often the culprits. Opioids Opioids have an inhibitory effect on gut motility and are respiratory depressants. Theoretically, these properties could pose a risk in a species, such as rabbits, in which slow gut motility is such a problem. However, in practice, the analgesic properties of these drugs outweigh the risk of slowing gut motility because the rabbit is more likely to eat if it is not in pain. Respiratory depression is not a problem so they are a useful class of drugs. Buprenorphine can be used. Its effects persist for 7 hours after administration. It can be used at the outset of anaesthesia to provide pre-emptive analgesia or postoperatively or for the treatment of painful conditions. Butorphanol provides a mild degree of analgesia and mild sedation but does not cause respiratory depression unless high dose rates are used. The effects last longer if the drug is give subcutaneously rather than intravenously. Tramadol is a synthetic analogue of codeine that does not possess the adverse effects of respiratory depression, slow gut motility or sedation although it can cause dysphoria in humans and cats. It is useful in rabbits and can be given alongside opioids and NSAIDS. Fentanyl patches (12.5mcg/kg/hour for most rabbits) are useful for animals in severe pain. The fur must be shaved close to the skin and wiped with methylated spirit before stretching the skin, applying the patch and holding it in place for a minute or two. An area where the skin does not wrinkle on the dorsum between the shoulder blades is the best site to choose.

8 8 Post-operative care Although many owners believe they can manage their rabbit at home, it can be a mistake to discharge a rabbit too soon after an operation. Close observation is necessary, as gut stasis is a risk in any rabbit that has undergone surgery. If the rabbit is bright, alert and eating post-operatively it is safe to send it home, especially if the owner is sensible and informed. Providing owners with post-operative care sheets describing the signs of gut stasis is extremely useful. If there is any doubt about the rabbit going home, hospitalisation is preferable so the nursing staff can observe the rabbit carefully, ensure that all medication is given, provide nutritional support, provide analgesia and comfort, and attend to any wounds effectively. Demeanour, food and water intake, urine and faecal output are easy to monitor and record on a hospital sheet. Hospitalising bonded companions There are disadvantages and advantages associated with bonded companions. Cage size can be a problem, especially if the rabbits are large; also two rabbits produce twice the amount of mess. It is difficult to know for certain that both rabbits are eating well and passing faeces. Sometimes they need to be split up to find out, which seems a shame for the healthy one. It is worth remembering that the healthy companion might be stressed by staying at the vets and could develop gut stasis. The advantages of hospitalising a companion are that it might reduce stress levels and it avoids the risk of the rabbits fighting when they are re-introduced. Fluid therapy It is important to provide water in an acceptable form for the rabbit. It has been shown that they will drink more from a bowl than a sipper bottle. As in other species, fluids can be given intravenously, orally, subcutaneously, intra-peritoneally or intra-osseously. Intravenous fluids are necessary for dehydrated rabbits (e.g. with diarrhoea) or for shocked rabbits (e.g. with an intestinal obstruction) but are not necessary for rabbits in the early stages of gut stasis. Oral fluids (in the form of a syringe feed) are enough to provide essential fluids and electrolytes. There are fewer complications, such as the rabbit chewing through the tubing or overperfusion. Subcutaneous fluids (10-20mls/kg) can be administered either into the scruff or into the loose skin over the chest. They are most useful to induce diuresis e.g. in rabbits with sludgy urine. Prevention of gut stasis Pain control, stress reduction and food are all important in the prevention of post-operative gut stasis. It is important to give analgesics. A comfortable quiet, warm (but not too hot) environment with plenty of tempting foods is important. Diet Good hay, freshly picked grass and dandelions or palatable vegetables such as kale, spring cabbage or carrot tops are beneficial. It is a good idea for owners to leave some favourite foods with their rabbit or fill in a menu sheet so the nursing staff know what the rabbit likes to eat. Some rabbits will eat straightaway, despite extensive surgery. Others refuse to eat, despite minimal surgery. House-rabbits may not eat just because they are away from home. Syringe feeding Syringe feeding is necessary for any rabbit that does not eat or is struggling to eat because of dental or problems or other conditions that make eating difficult. Various foods are available from syringe feeding. A 50:50 combination of Oxbow Critical Care and baby cereal works well (e.g. Heinz cereal for babies aged 4-6 months) because the cereal is fruit flavoured and palatable. It also has no lumps and goes through a syringe easily. Approximately 10-20ml/kg of the mixture four times daily is a satisfactory amount - some nurses are better at this than others.

9 9 Prokinetic therapy Prokinetic therapy is indicated for those rabbits that are not passing hard faeces or are only passing small ones. Different medications are available in different countries. In UK, domperidone (0.5mg/kg) or metoclopramide (0.5mg/kg) are used. Administration of medication It is extremely valuable to draw up a chart (a ready-reckoner) of the medications that are used in the practice for rabbits. It means that dose rates are already calculated according to the rabbit's weight so arithmetical mistakes are less likely. An accurate set of scales (for weights under 10Kg) are necessary. Oral Medications Many rabbits are easy to dose with oral liquids. Many of them enjoy sweet compounds and will readily accept paediatric syrups. Medicating the drinking water is unsatisfactory but rabbits can be given tablets, which can be placed in the mouth or crushed in water. Some rabbits will take oral medication mixed with favourite foods Subcutaneous injections The subcutaneous route is suitable for the administration of most parenteral medications with the exception of some anaesthetic agents. Subcutaneous injections are well tolerated and owners can easily inject their rabbit without problems, although they may need to be shown how. Occasionally subcutaneous injections of antibiotics or vaccines can result in a skin reaction that may not be noticed until a few days later. These reactions can be minimised by making sure that the needle has penetrated the skin and the medication is injected subdermally rather than intradermally. Massaging the area after giving the injection is also useful. Intramuscular Injections Although drug manufacturers often recommend the intramuscular route, there are only a few products that really have been given intramuscularly to rabbits. Subcutaneous injections are less painful. It is the anaesthetic drugs that give effects that are more predictable if they are given intramuscularly. Atipamazole should be given IM. The lumbar muscle mass or the cranial muscle mass (quadriceps) of the hind leg are the preferred sites. The caudal muscle mass of the hind leg should be avoided because of the sciatic nerve. Self-mutilation of the foot has been reported in rabbits as a result of nerve damage during intramuscular injection of ketamine and xylazine into the caudal muscle mass. If large volumes (>0.5ml/kg) are to be given intramuscularly, the dose should be divided and given in two sites. Intravenous injections The usual site for intravenous injection is the marginal ear vein that is accessible and easily visualised in rabbits. Rabbits can be restrained by wrapping them in a towel. A sharp pair of curved scissors, small gauge needles, adequate light and good eyesight are required especially in dwarf breeds. Good blood pressure makes life easier. It can be difficult to find a vein in collapsed or shocked rabbits. An alternative site is the cephalic vein similar to the dog or cat but the rabbit's short legs sometimes makes raising the vein difficult. Other veins such as the jugular or femoral veins can be used and the choice is largely a matter of individual preference. Intravenous fluid therapy The choice of sites is more limited for intravenous catheterisation and fluid therapy. The femoral or jugular veins are impractical. Usually the marginal ear vein or cephalic vein is used due to the ease of keeping the rabbit in the correct position for intravenous fluids to run once the drip is set up. Some practitioners favour the cephalic vein. Intravenous catheters or cannulae can be held in place with adhesive tape

10 10 No bandaging is required to keep the intravenous cannula in place in sedated or moribund patients, although a piece of bandage tied around the rabbit s neck can be used to hold the giving set out of the way. If the rabbit is well enough to chew through the tubing, it probably does not need intravenous fluids anyway. Intravenous fluids into the ear vein can cause problems. Some products are irritant and can cause tissue necrosis. Diazepam and carprofen are examples. Indwelling catheters are not recommended. They can introduce infection and are uncomfortable. Nose drops Rabbits tolerate nose drops well. They are a useful way to administer topical antibiotic therapy for rhinitis. Generic gentamicin drops are very useful (also for abscesses). Intranasal midazolam (0.5-2mg/kg) can be given to rabbits that are having seizures. Nebulisation Nebulisation can be used as an adjunct to treatment of upper and lower respiratory tract disease in rabbits. A variety of medications, such as antibiotics, can be mixed with warm saline (38 C) and administered twice a day, via a nebuliser, into the air space of a small cage containing the rabbit. Nasogastric or nasoesophageal tubes Although many authors describe the use of a nasoesophageal or nasogastric feeding tube to administer nutritional support, they are rarely, or never, necessary. The tip of the tube is placed either in the oesophagus or in the stomach and the tube is usually kept in place by suturing it to the nares and/or skin on the face or head. Although these tubes permit easy administration of liquid food, they have many disadvantages: Nasogastric tubes create an opening in the cardiac sphincter that can allow reflux of acidic gastric contents into the oesophagus that may cause inflammation and possible stricture formation Nasoesophageal tubes deliver food into the oesophagus rather than the stomach so there is a risk of regurgitation or overflow of food into the pharynx. Choking or inhalational pneumonia may be the result. It is impossible to administer long particles of fibre through nasoesophageal or nasogastric tubes without blocking them, so only liquid food can be administered. The nasal mucosa of rabbits is very sensitive so inserting the tube and suturing it to the nostril can be stressful, even after the administration of local anaesthetic drops or gel. Placing the tube can damage the nasal mucosa and cause epistaxis. Nasogastric or nasoesophageal tubes are contraindicated in rabbits with upper respiratory tract problems. They can cause further irritation to the nasal mucosa and exacerbate infection. After the tube has been placed, an Elizabethan collar is often necessary to prevent the rabbit removing the tube. Elizabethan collars add to the stress levels of the rabbit, and prevent caecotrophy. Stress increases the risk of anorexia and gut stasis.