Introduction

As the popularity of rabbits, ferrets, rodents, and other small mammals grows in the United States, more of these animals will be presented to veterinary hospitals for medical care. Unfortunately, whether they are presenting to an emergency clinic or a general practitioner, often these animals are presented to the veterinarian in advanced disease states and should be considered emergency cases. Critical care medicine for these species should follow the same protocols and guidelines described for domestic species. The purpose of this lecture is to provide veterinarians with an introduction to the management of emergent cases, critical care, and associated techniques that can be applied to exotic small mammal species.

History and Initial Assessment

On presentation, a thorough history should be taken that includes information pertaining to the signalment, the care and management of the animal, duration of illness, and other pertinent information that can be used to guide initial diagnostics and assessment. Specific information regarding husbandry of the animal can be crucial in determining the etiology of many disease states. While this initial information is being gathered, the animal should be placed into a warm, quiet, clean enclosure. If the animal is in respiratory distress, supplemental oxygen therapy is recommended.

Prior to a thorough physical examination, a visual examination should be performed. A hands-off visual examination will not only provide an initial triage assessment, but can also help dictate prognosis. This can allow for an open line of communication with the owners addressing the risks of restraint and diagnostics prior to handling. Observe the animal's general demeanor, respiratory rate and pattern, and ambulation. Overall appearance of the animal including hair coat, mentation, and cleanliness should also be noted. Signs of respiratory distress include open-mouth breathing, increased respiratory rate, change in depth and effort, and possible discharge from the nares. Rabbits and rodents are obligate nasal breathers, so open-mouth breathing can be a sign of both upper and lower respiratory disease. Abnormal sounds, including gurgling and clicking, are also indicators of respiratory disease. Animals with these clinical signs should be provided supplemental oxygen and handled only when necessary. The physical examination should be thorough and rapid. The animal should only be manipulated for short periods of time and given breaks if it appears weak or compromised.

Cardiopulmonary Resuscitation (CPR)

Cardiopulmonary resuscitation for an exotic small mammal should follow standard protocols that would be used in canine or feline medicine. Animals in respiratory arrest should be intubated and provided intermittent positive pressure ventilation when possible. Unfortunately, intubation in many of the exotic small mammal species may be difficult. Ferrets are the most easily intubated. The approach to intubating a ferret is similar to a cat. Most ferrets take a 2–4-mm endotracheal tube. Rabbits can be intubated; however, they are often intubated blindly, which requires active respiration. Alternatively, an endoscope may be used to assist in intubation. For many other rodents such as guinea pigs, chinchillas, or rats, intubation may not be possible. Doxapram (2–10 mg/kg) may be used as a respiratory stimulant in these cases.

The heart should be thoroughly evaluated by auscultation. If available, an ECG can be helpful in monitoring and further assessment. Bradycardia may be managed with atropine (0.05–0.5 mg/kg). However, keep in mind that many rabbits possess an endogenous atropinase. For this reason, it is often recommended to treat rabbits in an emergency situation with glycopyrrolate (0.01–0.1 mg/kg). In cases of asystole, epinephrine (0.1 mg/kg) should be administered via intracardiac injection or intratracheally. Chest compressions should also be initiated with asystole. The heart of most mammals is located at the point of the elbow. The ferret is an exception, with the ferret heart located more caudally due to a long thorax.

Fluid Therapy

Fluid therapy is a necessity in emergency medicine. Exotic small mammals that are moderately (6–8%) to severely (> 9%) dehydrated require intravenous (IV) or intraosseous (IO) fluid therapy. In larger exotic mammals, such as the rabbit or ferret, an intravenous catheter can be placed into the cephalic or lateral saphenous veins. However, the auricular vein, located on the lateral aspect of the pinna, is another appropriate catheter site in the rabbit. The catheter should be secured to the limb or ear using appropriate splint/bandage material. Tissue glue may also be used to secure the catheter. Intraosseous catheters are generally placed in the femur, but can also be placed in the tibia. These catheters generally require sedation/analgesia. With that in mind, if an animal is severely dehydrated or hypovolemic, it may be difficult to place an IV catheter. In an emergency situation it may be prudent to immediately place an IO catheter if the animal is obtunded, moribund, or arresting on presentation. This will allow for quicker access. An IO catheter should also be attempted in smaller animals needing emergency attention such as guinea pigs, rats, or sugar gliders. Animals that are mildly dehydrated (< 5%) and considered stable can be given fluids via the subcutaneous (SC) or oral route. Subcutaneous fluids can be given over the dorsum between the scapulae or along the lateral body wall. Oral delivery of fluids (PO) is the preferred route of administration when the animal is mildly dehydrated (< 5%) and has a functional gastrointestinal tract. This is often achieved in conjunction with syringe feeding.

The choice of fluids for a patient should be based on the animal's physiologic needs. When these needs are not immediately clear, a balanced electrolyte solution is preferred. Crystalloids, such as Normosol-R or M and lactated Ringer's solution (LRS), are non-protein-containing fluids often used with success in these animals. Crystalloid mixtures have also been recommended including the addition of dextrose to Normosol or LRS. Colloids such as hetastarch may be considered in cases with severe hypoproteinemia or shock and are often administered as an initial bolus prior to administration of crystalloids for treatment of hypovolemia. When attempting to rehydrate a patient, it is important to keep daily fluid requirements in mind. Rabbits, for example have a much higher daily fluid requirement than many small mammals at 100 ml/kg/day. Rodents are also slightly higher at 75 ml/kg/day, and ferrets are often treated more like a dog or a cat with a maintenance fluid rate of 40–60 ml/kg/day.

Therapeutics

Many of the therapeutics recommended for use in exotic small mammals are based on our understanding of these drugs in domestic species. These drugs are being administered off-label and veterinarians should account for the potential risks associated with their usage. The route of administration will depend upon drug bioavailability, owner and patient compliance, and ease of administration. In general, therapeutics are administered to small exotic mammals via intramuscular (IM) injection, subcutaneous (SC) injection, or orally. Intramuscular injections are primarily given in the large muscles of the rear legs (e.g., quadriceps) or the epaxial muscles. When giving an IM injection in the rear leg, the needle should be directed away from the femur and sciatic nerve. Subcutaneous injections are generally given over the dorsum of the patient in the area between the scapulae.

Supportive Care

Anorexia is a common problem in sick and debilitated small exotic mammal patients. Critical patients need to be provided energy/calories to meet their metabolic needs. Oral administration of medications can become increasingly difficult as animals become more intolerant of being restrained. Animals that have been anorectic for an extended period of time should be gradually provided their caloric needs over several days to prevent a re-feeding syndrome, which can cause a life-threatening hypokalemia and hypophosphatemia. It is extremely important that hindgut fermenters, such as rabbits, guinea pigs, and chinchillas, have proper nutrition at all times. A short period, such as 12–24 hours, of not eating in these animals can result in a life-threatening dysbiosis or enterotoxemia. If they are critical and are not eating on their own or with assisted syringe feedings, a nasogastric tube can be easily placed under sedation in a similar technique to a domestic mammal. When administering pre-formulated diets through these small nasogastric tubes, ensure you are using a fine grind liquid diet formulation (e.g., Oxbow Critical Care Fine Grind, Murdock, NE) and flushing the tube to avoid loss of patency.

Specific Presentations

Fracture/Trauma

When a patient presents with a fracture, it should be stabilized immediately to reduce further bone damage, soft-tissue damage, and pain. Tape splints and Robert Jones splints may be used to stabilize distal limb fractures. These splints will prevent rotation of the fracture and stabilize the injury until appropriate diagnostic tests (e.g., radiographs) can be performed. The fracture should always be stabilized by including the joints above and below the fracture. Analgesics should also be given to reduce discomfort and pain associated with the fracture. In cases of severe open fracture, amputation may be considered.

Ferrets

Ferrets will often present for metabolic emergencies such as hypoglycemia/insulinoma. This should be the primary differential for a ferret over 3 years old with weakness, collapse, seizures, ptyalism, vomiting, or posterior paresis. After initial assessment, a blood glucose should be the first diagnostic test performed. In cases of insulinoma, blood glucose is typically less than 70 mg/dL. If ferret is seizing or unconscious, an IV or IO catheter should be placed and 50% dextrose should be bolused to effect (usually 1–2 mL). Karo syrup can also be placed on the gums. After this initial bolus, corticosteroids (dexamethasone SP 0.5–1 mg/kg) should immediately be started IV. It is very important to have a high-protein/high-fat diet available at all times. If the ferret is not critical, try to avoid giving dextrose, and instead syringe feed (Hill's A/D or Oxbow Carnivore Care) if it is awake enough to swallow. If possible, dextrose or sugars should be avoided as it may stimulate the tumor to secrete more insulin.

Two other common ferret emergency presentations include gastrointestinal foreign bodies (often in young ferrets) and urinary obstruction in males secondary to adrenal disease. Foreign bodies in ferrets can often be chronic with only a partial obstruction and can present with chronic or waxing-and-waning gastrointestinal (GI) signs such as anorexia, lethargy, and diarrhea. They are not always readily diagnosed on a radiograph and may require ultrasound or clinical suspicion to dictate the decision to go to surgery. Often urinary obstruction is caused by prostatomegaly in male ferrets with adrenal disease; however, uroliths or neoplasia are other possible differentials for urinary obstruction. An obstructed male ferret should be treated similarly to a male cat, keeping in mind that urinary catheterization can be challenging. After the obstruction is relieved, the owners need to be prepared for treating adrenal disease if this is identified as the primary cause.

Rabbits and Rodents

As prey species, rabbits and rodents are commonly presented on an emergency basis since they are often masking clinical signs as long as possible. For that reason, these emergency cases can be challenging. If an animal is presenting in shock or in need of CPR, regardless of therapy prognosis is grave due to the vascular compromise of the GI tract.

Rabbits are easily stressed and handling should be minimalized in the case of these animals. A rabbit or rodent's GI tract is also very sensitive and if given the wrong antibiotic, a gram-negative or clostridial overgrowth may develop, which can be fatal. Macrolides, lincosamides, and beta lactams are unsafe to administer to rabbits and hindgut fermenting rodents such as guinea pigs and chinchillas. Some safe antibiotics include fluoroquinolones, trimethoprim-sulfa, and metronidazole.

While rabbits can present on an emergency for many reasons, gastrointestinal emergencies are the most common, which can include GI stasis, dental disease, diarrhea, or GI obstruction. Gastrointestinal stasis is commonly a clinical sign versus a primary disease process. With that in mind, regardless of the cause of GI stasis, the severity can range from mild to life-threatening. A thorough oral examination should always be performed as dental disease can often lead to decreased food intake. Clinical signs may include interest in food but inability to swallow, difficulty eating hay, and ptyalism or "slobbers." Once an obstruction is ruled out on physical examination and radiographs, therapy often includes rehydration (SC or IV fluids depending on severity), force feeding (liquid critical care diet), promotility agents that will work throughout the entire length of the GI tract such as cisapride (0.5 mg/kg PO BID), and pain management. Since these patients are often presented somewhat dehydrated, it is not initially recommended to use an NSAID due to the risk of renal damage. For this reason opioids are often used. However, since they can cause constipation and decreased GI motility in other species, they must be used with caution.