Principles and techniques in exotic-mammal surgery (Proceedings)

Soft tissue surgery is commonly performed on small exotic mammals for preventative health, control of reproduction, and to manage conditions warranting surgical intervention.  The principles of surgery for dogs and cats also apply to cases involving exotic pets.  However, paying attention to certain principles becomes more critical due to the small patent size and characteristics.  Preparing the patient and owner for surgery is important for a successful outcome.  Pre-operative patient assessment should include an accurate weight determination, evaluation of hydration status, optimizing body condition, and in some cases, an evaluation of pre-operative blood parameters.

Surgical preparation

Fasting of the patient is dictated by its gastrointestinal anatomy and physiology.  Small exotic herbivores, especially those that have hind-gut fermentative digestion, are rarely fasted.  As a general rule, these species cannot vomit and have slow GI transit times.  The goal of fasting in these species (3-6 hours) is a relative emptying of the mouth to prevent aspiration during anesthetic induction and intubation.  Small mammal carnivores, such as ferrets, have short GI transit times and are often fasted prior to surgery (4-6 hours).  Young and old animals that may be affected significantly by hypoglycemia should not be fasted more than 6 hours.

Whenever possible, the surgical patient should be well hydrated, calm, and normothermic.  Pre-operative blood work, when necessary, should be performed prior to the day of surgery as long as the condition of the animal is not likely to change.  This will prevent unnecessary blood loss that might compromise the patient during surgery.  Fluid administration performed orally or parenterally prior to surgery will allow the practitioner to be confident that the patient is well hydrated and that blood pressure will be optimal.

Pre-operative concerns

Pre-operative medications are aimed at keeping the patient pain-free and stress-free.  Buprenorphine provides excellent analgesia and mild sedation for small mammals.  Butorphanol has rapid effect but doesn't last as long as buprenorphine.  Combining an opiod analgesic with midazolam provides excellent sedation for the small mammal patient.  Parasympatholytic medications are beneficial if patients become bradycardic during induction.  Atropine is the drug of choice for most small mammals but glycopyrolate is indicated for rabbits as they have increased atropinase levels.

Obtaining vascular access for surgical patients is optimal.  Intravenous (IV) catheter placement is routinely possible in most small mammals using 24-26 gauge IV catheters.  Some patients, such as ferrets and guinea pigs, have tough skin requiring that the skin be nicked over the vein of choice prior to catheter placement.  When an IV catheter cannot be placed, the clinician will need to weigh the risk of not having vascular access during surgery against the potential morbidity associated with an intraosseous catheter.  IO catheters are easily placed in the proximal tibia of most small mammal patients.  IO and IV catheter placement is often facilitated by placing the patient under anesthesia prior to placing the catheter.  Fluids should be provided during surgery at a rate of 10 ml/kg/hr and ideally are warmed prior to administration.  A syringe pump is a useful tool for providing slow administration of fluids to small patients.

Anesthetic induction

Several injectable anesthetic protocols are published for small mammal surgery.  However, small patient size and the need for finely tuned control over anesthetic depth make inhalant anesthesia options preferred.  Isoflurane and sevoflurane have both been used with excellent results.  Induction is often achieved by mask administration of anesthetic gas or by placing the patient in an induction chamber.  Once anesthetized, intubation should be performed if possible (routinely performed with rabbits and ferrets).  If intubation is not feasible, continuing anesthetic administration by mask is required.  Intubation of small mammals requires small non-cuffed endotracheal tubes (2.0 ID).  Alternately, a red-rubber tube can be modified to serve as an endotracheal tube.  Visualization of the larynx can be facilitated by use of endoscopy equipment or a small laryngoscope when necessary.

Surgery

Surgical preparation of small mammal surgery patients is identical to that of domestic species.  Rabbits have thick fur and thin skin.  A #50 clipper blade will effectively clip the hair in most cases.  Achieving and maintaining hemostasis is critical for small mammal patients.  Many times the patient is less than 2.0 kg and they have a small total blood volume (~50-80ml/kg).  Electrosurgical units, surgical clips, and clot-promoting materials are extremely useful in limiting blood loss intra-operatively.  Small patient size speeds the rate of heat loss during surgery.  Heat producing products such as water-circulating heat pads, heat lamps, and warm air blowers help maintain the patient's body temperature.  Clear plastic surgical drapes allow for patient visualization but also help insulate the patient to prevent heat loss through the drape material.

Visualization of the surgical site is hampered by the small patient size.  Surgical magnification is ideal for all clinicians, even those who have excellent vision.  Operating loops or surgical glasses allow the surgeon to achieve precise movements and conserve time in surgery.  A focused light source is also useful.  The surgical field is often very small and visualization is optimized by the use of surgical retractors.  Microsurgical instruments not only allow for precise tissue handling but are also ergonomic.  All of these factors affect the length of time the patient will be under anesthesia.  Because of their high susceptibility to hypotension, heat loss, and other negative effects of anesthesia, it is crucial that small mammal surgical times be kept to a minimum.

Closure of surgical incisions is performed with small monofilament suture (3-0 – 5-0) and skin is closed in buried suture patterns to prevent premature self-removal by the patient. This is especially important in the case of rabbits and rodents.  Stainless steel suture and skin staples can also be used and are not easily removed by the patient.

Post-operative concerns

Small mammals recovering from surgery are often hypothermic and benefit from thermal support post-operatively.  Temperature controlled incubators, heating discs, and heating pads can be used to this end. Of note, many small mammal species are susceptible to heat stress and hyperthermia and as such should be monitored hourly while receiving supplemental heat.  Once recovered, it is critical to provide nutrition to small mammal patients.  Many of these patients will not self-feed making assisted feeding necessary.  Gruel based diets are available to facilitate assisted feeding (Oxbow Carnivore Care and Critical Care, etc).  Post-operative antimicrobial therapy should be considered for small mammals when the incision will be in contact with bedding or excrement around the caged enclosure.

Conclusion

The basic principles of surgery apply to surgical care of small mammal patients.  The small patient size does necessitate that some measures be taken to ensure a safe recovery.  By providing surgical care to small exotic mammals, the veterinary practice can grow while providing professional growth and enjoyment for the clinician. 

Resources

Current Techniques in Small Animal Surgery, 4th ed. Bojrab M.J., ed. 1998. Lippincott, Williams, & Wilkins, Philadelphia, PA.

Ferrets, Rabbits, and Rodents; Clinical Medicine and Surgery, 2nd ed. Quesenberry K.E., Carpenter J.W., eds. 2004, Saunders, Philadelphia, PA.

The Veterinary Clinics of North America – Exotic Animal Practice; Soft-Tissue Surgery. Bennett R.A., ed. 2000. W.B. Saunders Co., Philadelphia, PA.