CRITICAL CARE OF Eric Klaphake, DVM, DABVP (Avian), DACZM, DABVP (Reptile-Amphibian) , Springs, CO

The term “emergency” obviously means different things to different people. My definition of an emergency is an issue which requires immediate intervention to prevent death, irreversible disease/injury progression, or pain. However, a client’s definition(s) of emergency often include: they “just noticed the problem,” “this was a convenient time to come in,” they “starting to feel guilty about the issue,” they “thought it would die a long time ago, and it has not,” and of course anything involving blood. Another possibility to consider is something normal appearing to an individual not aware that such things are normal in that species. Trying to summarize all the emergencies that might be seen is beyond the scope of a one hour lecture, however; the most common presentations for rabbits will be covered. With exotic animals, problems may present at a very advanced stage or clients may not have the finances/desire to pay for the more advanced diagnostics and therapeutics that can be provided with what they view as a disposable pet. Therefore, you may need to have The Quality of Life Talk sooner than one might expect. While one should always offer the highest level of care or referral, many times this is the first time an individual has brought a into a veterinarian and they often expect cost of care to reflect size of animal. As with all animals, emergencies often place the client into a very emotional state. As a veterinary team, our first job is to manage the welfare of the patient, however, we also have to be very careful about discounting or not receiving proper payment for our services. Once stabilized, clients should be provided both the short term picture and prognosis, but also provided a longer term view of where things may be headed. A common question asked to both the veterinarian is “If it was your ….” I prefer to always answer this honestly and often provide two forms of answer: “if this pet means everything to me (or my child)”, and “if I care about the animal’s well-being and do not want it to suffer, but there are limits to where I want to go.” Unfortunately, euthanasia as an option becomes the gorilla in the room, but should be discussed from the very beginning if it is a viable option. With some of these presenting conditions, providing client guidance as to

determining points of exit can be helpful, along with providing hospice care versus hospitalized care or euthanasia options only. A finally challenge with many exotics are owner-present euthanasias. Many times, the final injection will be delivered intracardiac, so preparing a client for this is critical. It goes without saying that intracardiac injections without prior general anesthesia are considered inhumane in any animal.

GENERALITIES

The following are general recommendations for common issues that clients may call the clinic regarding and suggested advice to provide.

* Minor bleeding- apply direct pressure to the area for 5-10 minutes. Come in if not stopping.

* Major bleeding - apply direct pressure to the area and come in immediately.

* Minor bleeding from the toe nail - apply kwik stop, cornstarch, flour or a bar of soap to the nail. Come in if not stopping.

* Diarrhea-If allowed to go untreated, the animal can become dehydrated quickly.

* Decreased appetite/fecal production- If a drop in the animal’s weight, decreased interest in food, decreased amount of fecal production, or increased salivation, come in sooner versus later.

* Hyperthermia- Most small mammals cannot tolerate high temperatures above 85-90 F. The animal will be collapsed and panting. Mist with cool water and put ice packs near the animal. Soaking an animal in cold water can send them into shock and further complicate the situation. Bring in immediately.

* Coughing, sneezing, runny nose, eye discharge, and open mouth breathing are symptoms of respiratory distress. Keep the animal warm (75-80 F) and quiet with minimal handling, and bring in immediately.

BIG 3 PRESENTATIONS

While not completely correct, remember that rabbits are basically “stomachs wrapped in fur” and that their gastrointestinal systems function most closely to that of a horse, so triage and treat in a similar manner. Rabbits are considered geriatric at five years of age. Like ferrets, pet rabbits are often allowed free roam of the house, there is no such thing as “rabbit proofed,” they often interact directly with dogs/cats, and they love to eat/chew on bad things. Three common presentations of pet rabbits are described below.

The most common presentation is the rabbit that is not eating nor defecating, with variations such as: eating, not defecating; not eating, but defecating; or eating and defecating but not in a normal manner. The most common issue is usually dehydration. However, other rule outs include: trichobezoars, foreign bodies, toxins, incorrect diet, incorrect use of antibiotics, dental disease, and neoplasia. Once the rabbit is stable, initial diagnostics should include: a complete blood cell count, serum chemistries, and radiographs. Placement of an IV or IO catheter may be warranted, but can be challenging to maintain in these rabbits unless they are extremely lethargic, as they often chew through the catheter lines. In many cases, SQ fluids are a better way to go, however, if the rabbit is shocky, this may not be the best method to attempt. I generally administer 150 mL/kg as a bolus, and if absorbing well, repeat every 6-8 hours as indicated. If gastrointestinal motility is a concern, injectable treatment versus oral medication is preferred. Nutritional support (a fine grind herbivore critical care) should be initiated. If a foreign body seems unlikely, then metoclopramide should be considered. Supplementation with famotidine and maropiant may of benefit. Pain management should be an important component of managing the case, considering that gastrointestinal distention can be extremely painful, including the use of NSAID’s and/or opioids (remember the latter can have gastrointestinal motility effects). With rabbits, it is critical to be aware that certain drugs can cause severe problems in rabbits, including: systemic corticosteroids, fipronil, and oral penicillins/cephalosporins.

A second common presentation in rabbits is ocular discharge/facial swelling. Clinical signs can include: unilateral or bilateral ocular discharge and soft or firm swellings on the face. Rule outs include: pasteurellosis, tooth root abscess, nasolacrimal duct blockage, allergies, an ocular foreign body, neoplasias, and overgrown molars/premolars. Initial diagnostics should include: a complete blood cell count, serum chemistries, radiographs, bacterial and fungal culture sensitivity and cytology of discharge and/or swelling, an oral examination under anesthesia, and a nasolacrimal duct flush. Fluid therapy may be necessary as described previously. If the teeth appear abnormal with an anesthetic exam or via dental radiography, trims and/or

extractions may be necessary. As rabbit pus does not drain well, surgical excision of defined abscesses or neoplasias may be warranted. For difficult locations of abscesses, incomplete removals, or in critical patients, the use of honey or super-saturated sugar packing techniques may be of value. For cultures, it is of greatest value to submit a piece of the abscess wall rather than aspirated pus, as the latter is often actually sterile. When culture is not an option, parenteral penicillin can be considered, as it will not influence GI dysbiosis as much as oral treatment. Antibiotic-impregnated polymethylmethacralate beads can be effective to pack an infected site, with antibiotic selection based on culture and ability to be incorporated into the beads. Pain management needs to be considered as well for both the disease as well as for potential treatments.

A final common presentation is the rabbit with a head tilt, ataxia, or circling. Clinical signs can include the aforementioned, along with nystagmus, rolling, and hyperesthesia. Rule outs include: pasteurellosis, trauma, Encephalitozoan cuniculi, toxoplasmosis, heat stroke, neoplasia, hepatic disease, and ear mites. Initial diagnostics should include: a complete blood cell count, serum chemistries, radiographs, and an otic examination under sedation—rabbits are extremely touchy about ear evaluation. If available, a CT scan may provide a better evaluation of more subtle disease. Other tests to consider include a Pasteurella titer, an E. cuniculi titer, and toxoplasmosis titers (IgG and IgM). While these can all be run, the value and interpretation of single values is debatable. Ideally, paired titers (two to four weeks apart) sent in together are the gold standard, but of little use in the here and now. Again the benefits of injectable treatments, nutritional support, fluids, metaclopramide, and pain management should be assessed. Other medications, such as corticosteroids (despite the extreme sensitivity of rabbits to this class of drugs), albendazole, and prophylactic antibiotics such as enrofloxacin or a sulfa drug may be considered by the veterinarian.

Other emergency rabbit presentations can include: caudal paresis, heat stroke, ripped off limbs, fractures, bloat, severe pruritis, overgrown/broken off incisors, screaming rabbits, fecal matting of the perineal region (usually diarrhea), urine scald, “sandoliths” (rabbits tend to get calcium sand obstruction of the urethra vs a stone form), maggots (and a slight permutation—Cuterebra), and broken off toenails. With neurologic presentations, do not forget they are mammals and rabies can occur.

NORMAL GI ANATOMY AND PHYSIOLOGY

Rabbits in the wild use their sensitive lips to grasp their food. These have specialized receptors that help to compensate for the fact that because of rabbit ocular positioning, they can not see what is happening by the

mouth. They have a long diastema, rostrally positioned incisor teeth and a cleft upper lip (‘‘hare-lip’’). The food is then ground by the premolars and molars. The teeth in each of the four arcades, function as a single occlusive surface, as if there are only four cheek teeth. The margins of each tooth, and the ridge running from the labial to the vestibular surface across the occlusal surface of each tooth, are composed of enamel, with the remaining tooth surface formed from ‘softer’ dentin. The pattern of wear on soft versus hard maintains a file- like occlusal plane on each arcade, Actual mastication is a complex interplay of the jaws, teeth, and tongue. Masticatory actions are divided into three types. The stomach has a thin-walled cardia and fundus and a thicker pyloric region, in total comprising 15% of GI volume, with a well-developed cardiac sphincter that disallows vomiting. Churning of food material in the cardia occurs because of large intestinal movements and locomotion. The stomach is normally never empty, even with a 24-hour fast, it is still 50% full, food/hair surrounded by fluid. Gastric pH in adults is 1–2, which destroys most organisms, maintaining an almost sterile stomach and small intestine. Food stays 3–6 hours here. Gut motility can be divided into several different processes. At the distal end of the ileum, dorsal to the large intestine in the left caudal abdominal quadrant, there is a round, muscular ampulla referred to as the sacculus rotundus that has an immunological role, is only found in rabbits, and is one of the most common sites for foreign body obstruction. An ileocecal valve between the ileum and the sacculus slows reverse flow of fluid into the ileum, and directs chyme via the sacculus rotundus to the cecum. The rabbit’s cecum is proportionally the largest of any mammal, being twice the length of the abdominal cavity and 40–60% of the total GI volume. It is a blind sac that folds into four complex parts (gyri). The appendix secretes bicarbonate into the cecum to buffer the volatile fatty acids produced by cecal fermentation. A low fiber and high fermentable carbohydrate diet leads to an enlarged appendix. The cecum provides an anaerobic fermentation chamber. Coliforms are rarely isolated, though likely present in low numbers. Lactobacillus spp. are absent from the normal intestinal flora of the rabbit. Many nonpathogenic protozoa are found in the cecal contents. The yeast Saccharomyces guttulatulus is often seen in fecal smears, appearing as if an unusual coccidia. Volatile fatty acids (VFAs) are actively absorbed and used as energy sources like ruminants. Rabbits differ in that butyric acid exceeds propionic acid. Proportions are 60–70% acetic, 15–20% butyric, and 10–15% propionic acid. Both increased fiber and fasting increase the proportion of acetic acid. Butyric acid may inhibit peristalsis, thus reduced butyric acid level may be why increased fiber promotes motility. The ascending colon is very long, and divided into five limbs extending forwards and back separated by flexures with taeniae and haustrae. Fecal pellets form at the end of the ascending colon. The transverse colon is short, and ends in a muscular thickening known as the fusus coli, again unique to rabbits, which often changes the terminology from three colon parts to two—proximal and distal. The fusus coli is a differential pacemaker for the initiation of peristaltic waves in the entire colon and regulates the separation of fermentable material from indigestible fiber.

Prostaglandins inhibit the motility of the proximal colon and stimulate the distal colon, aiding cecotroph production. The autonomic nervous system and adrenal glands in the regulation of the fusus may be why rabbits are prone to stress related gastrointestinal disease. Cecotrophs are produced at the anus from partially fermented matter rather than from unwanted fiber, so they are not true feces and therefore the ingestion process is not truly coprophagy. Cecotrophs are ingested due to response to a number of factors, including rectal mechanoreceptor stimulation, olfactory stimuli, and blood concentrations of various metabolites and hormones. In wild rabbits cecotrophy occurs in the day in their burrows, while in captivity, ingestion occurs at night. Cecotrophy usually follows about 4 hours after ingestion of food. The degree of cecotroph ingestion is directly related to fiber content. Cecotroph ingestion is highest when rabbits are fed on a diet high in nondigestible fiber. Most important to rabbit digestion is the regulation of colonic and cecal motility to allow the separation into indigestible and fermentable, being divided into a hard and soft feces phase.

DIET

Rabbits are biologically built to be folivores, ideally eating succulent plants. Their metabolism is contradictorily high for an animal on a high fiber diet. This balancing act takes a high food/energy intake system that partitions out the digestible and easily fermentable nutrients and quickly eliminates the slowly fermentable fibrous components. However, the same stuff the rabbit is trying to get rid of, is essential for keeping the gastrointestinal system happy. As most of us know, the most common cause of gastrointestinal problems is lack of this quickly eliminated fiber. In captivity, the succulent folivore grazing rabbit is generally not feasible, whether due to climate or environmental limits. Instead, they are fed a combination of dry leafy hay, extruded pellets, and some leafy greens that are meant to simulate those leafy plants. Many clients focus exclusively on pellets, even adding in seeds, nuts, dry starches, fruits, and starchy vegetables. Often, these rabbits surprisingly seem to process these diets adequately; however, over time these abnormal diets are a version of ultimate Russian roulette, with the rabbit eventually developing diarrhea and potentially deadly complications. Alfalfa, the most common type of pellet and quite commonly offered as hay, is actually a legume, like beans or peas rather than an actual grass. There are three issues with alfalfa for rabbits, especially as a significant portion of the diet. First, it is extremely high in calories, which is great if one is raising a rabbit for fur, meat, or research and therefore long life expectancy is not critical. However, obesity is a significant problem in house rabbits, and one of the contributing factors obviously is too many calories. Secondly, alfalfa has a lower level of fiber than grasses and grass pellets. Finally, alfalfa is very high in calcium. While not within the scope of this topic, another critical aspect of diet is the calcium content, particularly the pellets. Unfortunately, veterinary medicine

is still uncertain what levels of calcium at different lifestages are beneficial or harmful in rabbits, when considering the skeletal and urinary systems among others. Ideally, an alfalfa-based pellet is at most fed during the early growth stages of the rabbit, and that by six months of age and beyond, the rabbit is converted to a timothy hay-based pellet. Even this component of the diet needs to be monitored to provide the correct amount and to avoid unneeded calories. Likewise, hay should be limited to only grass hays, such as timothy and orchard grass. Be aware that many hay fields for horses can contain a component of alfalfa, so it is prudent to determine the percentages of types of grass. The final aspect of diet for the typical indoor rabbit is the leafy greens. There is a large laundry list of potential greens, but to provide variety and make it easier for the owner, the pre- packaged spring mix greens should be considered. There have been concerns that feeding too many greens can lead to diarrhea, however, as discussed previously, succulent leaves are the normal core component of wild rabbit diets. Where problems seem to arise is introducing this component of the diet to a rabbit previously not exposed to greens, in large volumes, versus gradual introduction. Thicker vegetables, fruits, nuts, and the colorful cereal components of some “deluxe” pelleted diets should NOT be fed to rabbits. The primary concern is that all of these items are starches. In the GI system, they are broken down from complex carbohydrates to simple sugars. Sugars are acidic. This acid wash hits the normally basic pH of the lower GI and can significantly alter the microflora. Problems include death of normal organisms, leading to overgrowth of undesired organisms or the release of endotoxins from dying commensal organisms. In most cases, the rabbit manages this GI upset with no obvious outward clinical signs. However, over time the odds that this will cause a problem do rise. As stated before, most causes of diarrhea in the rabbit can be attributed to incorrect diet.

DENTITION AND DENTAL DISEASE

After diet, this is second most common cause of GI disease in rabbits. With open-rooted, constantly growing teeth, there is obviously good cause for problems. Throw in a diet that is different from in the wild and the fact that biologically, these animals are not meant to live as long as they do in captivity, and such problems are explainable. Generally, dental disease in rabbits consists of one of two forms—that above the surface of the gingiva, and that below—the proverbial “iceberg.” So skull radiographs are critical to evaluate both parts of each tooth. A recent paper by Boehmer in 2009, developed an objective scale to evaluate the tooth roots. Starting in the front of the arcade, there are four maxillary incisors (two obvious and two “peg teeth” directly caudal to the obvious ones) and two mandibular incisors. Problems can include mandibular prognathism, due to genetic issues that are a concerning issue because of the lack of an occlusal surface for constantly growing teeth. While the incisors can be of great importance for the wild rabbit for slicing leaves off the plant, the

captive diet tends to render these incisors of questionable necessity, hence the reason that those teeth can be reasonably extracted with little detriment to the rabbit. If instead, an owner would prefer to have abnormal incisors “trimmed,” general anesthesia with masked isoflurane, followed by the use of a cutting disc on a dremmel can be used to reshape normal dental anatomy, though this will likely need to be repeated on a regular basis. However, it is extremely important to recreate the normal occlusal surfaces, which are actually cut edges, not smoothed off on the top. Normal healthy incisors do not need routine trimming. The cheek teeth are more challenging to address, and thorough evaluation requires general anesthesia and rabbit-specific dental implements to better visualize the teeth. Dremmels can be used for managing some dental overgrowth, however, as complete a dental evaluation as possible, mimicking those in dogs and cats should be performed including probing of gingival. Excellent PDF dental examination sheets are available on the Web. In some cases, extraction of these teeth may be necessary and are facilitated by special rabbit dental extraction instruments. Below the surface, roots can abscess, cause pain or impinge upon critical structures such as nerves, nasolacrimal ducts, and even the nasal passage. Initial clinical signs may present as non-GI in nature. Sharp points on the tongue can lacerate or entrap the tongue, however also consider electrical burns from cord chewing.

CATHETERS

The first question that arises on this topic is, does the rabbit need an intravenous (iv) catheter or not? Often, if there is not a high comfort level in placing these, the answer is that it does not. However, as with any animal, problems can occur, and when the veterinary team does not have ready vascular access during a crisis, regrets are common. As a veterinary technician, one of your most important jobs is to be an advocate for the patient and to double-check (overrule) the veterinarian on these issues. Often, the technician is the one performing the anesthetic monitoring during a procedure, and while the veterinarian makes the ultimate decisions on what is done to a patient, the technician is the one feeling guilty if anesthetic complications arise and they can not adequately try to address the problem. On the flip side, if it takes 20 minutes to finally get a catheter in, and the procedure would have taken 15 minutes, was that a worthwhile ancillary procedure to perform? When first starting to place catheters, it is often a good idea to set limits on the number of tries for catheter placement— two for the primary technician, one try for the “ace” technician, and one try for the veterinarian to make them realize how hard it really is on that particular animal. Everything should be ready to go before attempting placement to minimize handling stress. It also can often be very frustrating when first trying to place catheters to do so without some form of sedation or anesthesia.

At this point, the next question is where to place a catheter? There are a number of different options, and everyone has their own personal preferences based on expertise and experience. It may also depend on where a vein can actually be visualized or palpated. The most common sites for typical catheter placement in rabbits include the cephalic, lateral saphenous, and auricular (ear) veins. With the latter it important to realize a large artery runs next to vein and can lead to hematomas if lacerated. Stabilization by the rabbit holder and patience/confidence of the catheter placer are extremely important. Remember that many anesthetic agents decrease blood pressure peripherally, so that great veins seen during examination may become non-existent at catheter placement time. Often a single try on each vein is realistic. I usually start with the cephalic veins, move to the lateral saphenous veins before approaching the auricular veins. Others may start with the auricular veins, it just comes down to personal preference. Rabbit skin is quite thin like a kitten, but can still be surprisingly tough. I usually use a 24 gauge, 3/4th inch IV catheter, nicking the skin just lateral to the vein with a 22 gauge needle to avoid dulling the catheter. Start low on the vein, remembering that the catheter is 3/4th inches long, so forcing it to kink at the elbow or knee or having to keep part of the catheter outside the vein can lead to complications. In threading the vein, it is often more shallow than people think and is very fragile and therefore easy to go through. Many times, a small amount of blood will flash into the catheter, to indicate advancement of the catheter, though once it is in, blood may not flow as seen in dogs or cats, necessitating a small amount of heparinized flush to confirm. Do not try to aspirate back with blood, as this often clogs the catheter. Then secure the catheter to the skin with surgical glue, followed by the typical tape and self-adhesive wrap stabilizers. Reconfirm flow through the catheter, then either bolus desired amount of fluid or connect to fluid pump. Flush catheter at least every four hours. These catheters are often positional and seem to be more likely to be lost within several days, however; it is recommended to change iv catheters every three days if they do remain viable that long.

In cases where a catheter is critical but veins are blown or hard to locate, other options include a cutdown for cephalic, lateral saphenous or jugular veins or placement of an intraosseous (io) catheter. The author usually selects the latter, and utilizes the femur. The site is prepared as if for a bone marrow biopsy. Pre-measure the length of the catheter so it does not enter the knee joint. The distal femur is stabilized with the non-sterile hand and the bone isolated so that the io catheter can be guided down the middle of the femur, not coming out through one of the cortices. Once placed, do not try to pull blood back, instead flush the catheter (often flows slower than iv), if it is resisting, try replacing the stylet to remove any bone fragments. Place a tape butterfly on the hub of the needle and suture on each side to the skin. Obviously, these catheters pull out easily and if they are bent, become non-functional, but they are meant to be a short-term remedy anyways.

When awake, rabbits are notorious for chewing through iv lines, so monitor closely, and if otherwise bright, alert, and responsive, protect catheter and do not keep connected to a constant rate infusion system. Be careful about overflushing a catheter leading to heparin toxicity in these small mammals! Fluid rate and type obviously depend on the animal’s situation, but if performing a routine surgery, I start at 10 mL/kg/hr. If the rabbit presents in shock, I have no other information, and I cannot detect any overt evidence of cardiopulmonary disease, then I administer fluids at 100 mL/kg/hr to start and monitor respiratory sounds, eventually decreasing as the patient hopefully stabilizes. I personally will use a balanced electrolyte solution, spiking the potassium to 10 MEq/ L unless clinical signs or laboratory results suggest otherwise.

PHLEBOTOMY

Obviously, blood can be collected from the aforementioned vessels, but rabbit blood clots very quickly and the outflow rate of these vessels is often minimal. You can use a warm wash cloth applied to these vessels to try to increase local vasodilation. Some individuals are extremely skilled at jugular vein phlebotomy on rabbits, but the vessels are short and rabbits dislike head manipulation. Pre-heparinization of the syringe (1 mL or occasionally 3 mL syringe with either a 25 gauge or occasionally a 22 gauge needle) when performing phlebotomy in an awake or in shock rabbit is almost a must. If I need to save the previous vessels for catheter placement, need a larger quantity of blood, or the rabbit is being difficult/critical, I often will mask down the rabbit with gas anesthesia as described below and access either the jugular vein, or preferably perform a jugular notch stick. To do this, the rabbit is placed in dorsal recumbency, keeping the mask on the nose, straighten the body, pull the forelegs back towards the hind legs and insert a 25 gauge needle at the sternal notch towards one of the hind legs at no greater than a 45 degree angle. This is a blind stick and you are attempting to enter one of several major vessels in that area. Use the same care one would with a cystocentesis. Apply gentle back pressure to the syringe as you carefully enter deeper and shallower to find a vessel. If using gas anesthesia, even venous blood can appear bright red due to the increased oxygenation. There is no point in trying to hold often after removal, as the vessels are too deep. I have never lost any small mammal using this technique under anesthesia. With each new attempt, use a new needle. Often pre-heparinizing may not be needed, but can be helpful. Up to 1% body weight can be collected from a healthy rabbit (10 mL in a 1 kg rabbit).

ANESTHESIA

I usually continue to offer food to rabbits to within one hour of surgery since they cannot vomit/regurgitate and rarely collect food material in their mouth like guinea pigs do, long after they are done eating. If there are particles in there, I use cotton-tipped applicators to gently swab the mouth before intubating. I do not normally use atropine or glycopyrolate in small mammals for several reasons. In rabbits, up to 50% are reported to have atropinase, an enzyme that breaks down atropine, preventing its effects. More importantly, if their salivary/mucous secretions are made thicker, that makes me more nervous that a small plug of that will clog the already small endotracheal tube or trachea itself. If a catheter is already placed, iv ketamine/diazepam can be given. If a catheter is not placed (often a common scenario in a healthy rabbit), then I prefer giving some midazolam im, combined with buprenorphine, then chased with some ketamine once the previous two medications are on board. In some cases, I have tried im dexmedetomidine/ketamine, with good success, as long is aware of the significant effects of dexmedetomidine and to remember to reverse those effects after at least 30 minutes (to allow the ketamine to have reduced solo effects) with atipamezole. If a catheter is placed, propofol can be given iv, but in many cases, intubation can be attempted based on effect of pre-anesthetics/sedation. Another method that can be used to induce a rabbit is through the administration of a gas anesthetic through the use of a facemask applied to rabbit wrapped in a towel. Rabbits often hold their breath with mask/chamber induction, acting as if sedated until restraint is reduced, then trying to escape. I have also seen one case where a rabbit developed a conjunctival hematoma due to self-induced trauma from a face mask. Many clinicians prefer sevoflurane for induction due a more rapid onset and lack of such a strong odor as isoflurane. Based on the cost differential, I cannot recommend that it makes that much of a difference if a practice does not already have sevoflurane. I usually induce by starting with 0% gas, 2 L of oxygen through a non-rebreathing system and increase by 0.5% every two minutes. Maintenance depends on your system, individual animal sensitivity, seal of the mask, etc….. Once induced, it is important to remember that rabbits are obligate nasal breathers, so switching to a smaller mask and keeping a tight seal on the nose if you are not intubating is key. An entire facemask can still be used, but if an oral exam is needed or gas anesthesia is supplementing the attempt to intubate, a modified 6 mL syringe case as a mask can be very helpful.

Intubation is probably the trickiest technique to perform in a rabbit and takes a lot of repetition before one should be too confident in their abilities. There are many different approaches described, and finding the technique that is right for you is important. Some people prefer to intubate with the rabbit on its back, others prefer a blind approach, listening/feeling for a puff of air through the endotracheal tube before entering the trachea. Rabbit necks are quite short, so pre-measure and mark the endotracheal tube before placement to avoid intubation of a single lung. I usually intubate with a 2.0-3.0 diameter tube depending on the animals size. It is

usually a small space than most people realize. A drop of lidocaine on the larynx may or may not help as in rabbits. I avoid using tubes with cuffs, as this increases the material needed to get into the tracheal, and the risk for tracheal edema is present. I used to intubate using a rigid endoscope as the stylet in the endotracheal tube, visualizing the laryngeal cartilage before advancing the tube into the trachea. This works well, but requires expensive equipment. Currently, I place the rabbit in ventral recumbency, have my technician pull the head back towards the body (at least perpendicular) and keep the head/neck straight and extended. I grab the tongue with gauge and have the restraining technician hold it out as straight as possible or hold it myself with the same hand holding the laryngoscope. I use a 00 straight laryngoscope blade to visualize the epiglottis, which is often either farther back than one expects or is overshot by the intubator. Inside the endotracheal tube, I have a plastic/rubber coated stylet. Once the glottis is seen (remember the head must be extended and perpendicular!) the stylet is advanced into the glottis, inducing a cough, at this point the endotracheal tube is advanced down the stylet (blindly due to the limit visual field) into the trachea, and the stylet removed, possibly with a cough or not. Watch the tube for signs of fogging. Attempts to insufflate the “lungs” can look the same with the lungs or the stomach. Often the rabbit is breathing extremely shallow at this time. If confirmed in, tie with gauze the tube, being careful not to pull it out or to advance it. Do not attempt more than three tries to intubate to minimize laryngeal edema, and maintain on a mask if three unsuccessful attempts. Rabbits have died from aggressive, repeated intubation attempts. Once intubated, keep the thorax/head slightly elevated to minimize the pressure applied by the large intestinal tract on the relatively small chest.

Anesthetic monitoring is the same as you do with any other patient. Use pulse oximeters on feet/legs, ears (though this often fades once the animal has been anesthetized for awhile), lip, rectum, or tail. Applying alcohol periodically to the site or covering the probe with gauze to protect it from light can be helpful. Apply EKG leads as you would any other mammal. Esophageal stethoscopes work well. Indirect blood pressure measurements on fore or hind legs with the proper cuffs can work, and the old standby of direct cardiac auscultation is often overlooked. Capnograph monitors can be tricky due to the low flow rate coming from rabbits. Temperature probes are critical along with the use of hot-water blankets (or preferably Bair Blankets ®) are helpful to prevent hypothermia, though hyperthermia can also easily occur. Intermittent positive pressure ventilation is often necessary but remember the small lung size. Base your rate on patient status, but if uncertain, breathe every 15 seconds if not sure breathing on own or at least once a minute even if doing well to avoid shallow breathing and potential hypoxemia or decreased anesthetic effect. Apply pressure until you feel a small amount of resistance when using a non-rebreathing system, watch the chest for expansion response.

Remembering how challenging the intubation was, do not remove the endotracheal tube too quickly. Rabbits often recover very sedately and may need to be assess/encouraged to speed up the process with toe pinches. Recover on the floor or in a padded cage to minimize self-trauma. Most rabbits just lay/sit there during recovery, but continue to watch closely. Once staying upright, offer food immediately. If gastrointestinal compromise is possible, consider pre-emptive metoclopramide/famotidine/maropiant injections until eating and producing stool. Stool production may not occur for 12-24 hours after a major anesthetic episode. If I am concerned a rabbit is in/going into cardiac arrest, I grab epinephrine first and administer either iv or intracardiac. Once the heart has stopped, most attempts are more for the owner than to have any real chance of success in my opinion.

EUTHANASIA

If an iv or io catheter is in, follow the same techniques as you would with a dog or cat. I will usually use 1 mL of euthanasia solution per five pounds of rabbit, and often double that if the owner is going to be present. If a catheter is not placed, then I strongly recommend masking the rabbit down as described above with isoflurane or sevoflurane, and once deep pain is no longer present, then I will inject directly into the heart based on auscultating the point of maximum intensity. Make sure to inform an owner who wishes to be present what is being done and why. Attempts by the author to inject the smaller veins outside using the sternal notch site have usually met with frustration and hematomas when trying to inject anything, particularly something as viscous as euthanasia solution.

REFERENCE

1. Boehmer E, Crossley D. 2009. Objective interpretation of dental disease in rabbits, guinea pigs and chinchillas-- Use of anatomical reference lines. Tierärztl Prax; 37 (K): 250–260.