Written by Michael B. Mison, DVM, Diplomate ACVSR. Avery Bennett, DVM, MS, Diplomate ACVS
General Surgical Considerations
A complete thorough history including signalment, diet and appetite, and physical examination should be obtained before surgery. An attempt should be made to assess the level of stress that the animal is experiencing. The key to a successful surgical outcome in rabbits is minimizing stress, fear, and pain. Stresses associated with surgery have profound effects on their ability to survive surgical procedures. Anorexia, depression, and potentially death may occur following relatively minor surgical procedures. This is believed to be a result of increased catecholamine release. Also, this catecholamine release can influence the effects of various anesthetic agents making anesthesia challenging. The use of analgesics, anti-anxiety medications, and shorter hospital stays will help minimize the negative effects of the increased catecholamine release.
Rabbits are hindgut fermemters and a complex population of gastrointestinal microflora is re-sponsible for normal digestion. Diet change, antibiotic administration, and stress can alter ga-strointestinal function predisposing the patient to serious postoperative gastrointestinal complica-tions. Rabbits are unable to vomit making aspiration pneumonia of little concern. Since rabbits have a relatively large GI volume, many recommend a fast of 6-12 hr prior to laparotomy. This is intended to decrease the GI volume improving the surgical exposure and the ability to manipulate GI structures. This is unlikely to be of much benefit since it takes longer than this to significantly decrease cecal volume and fasting can have serious negative effects on blood glucose and GI motility. Because rabbits eat almost constantly, a short fast (1 hr) will empty the mouth reducing the risk of carrying food down the trachea during intubation.
Perioperative antibiotics may be administered just prior to perform¬ing the surgical procedure and maintained for a period of 24 hours postoperatively. Therapeutic antibiotics should be adminis-tered to rabbits with pre-existing evidence of infection such as snuffles. Since subclinical infec-tions can become clinical following the stress of even minor procedures, it is recommended that all rabbits undergoing a surgical procedure be placed on an antibiotic therapy for 7-10 days. An-tibiotics such as enrofloxacin, trimethoprim-sulfa combinations, sulfa drugs and aminoglycosides may be used safely in rabbits.
In most circumstances venous access for fluid therapy is recommended during surgery at a stan-dard anesthesia rate of 10 ml/kg/hr. A 20-24 gauge catheter can be placed in the cephalic vein of most rabbits for fluid support intraoperatively. As an alternative an intraosseous catheter may be placed in the femur in a normograde fashion inserting the spinal needle in the trochanteric fossa. The average blood volume of a rabbit is 57 ml/kg BW and loss of 15-20% of the blood volume results in a dangerous catecholamine release. Hemodynamic collapse and shock occur after loss of 20-30% of the blood volume.
Because of their small size and large surface to volume ratio rabbits are prone to development of hypothermia during general anesthesia. Attention must be paid to maintaining the patient’s body temperature which should be monitored throughout the procedure. A heated surgery table or cir-culating water blanket is necessary during long procedures on small patients.
Rabbits have very thin skin and very fine dense fur which is difficult to clip. Clippers often cut the skin and the blades become clogged with the fine dense hair. It is best to spread the skin flat, placing the #40 blade flat along the surface of the skin. It is important not to rush and not rake the blade across the skin as this will cause lacerations. The blades should be lubricated and cleared of the fine hair frequently.
Postoperative analgesia is recommended for rabbits. The success of surgery is often dependent on minimizing pain, fear and stress. Butorphanol may be administered at 1-5 mg/kg q 4-6 hrs SQ or 0.1-0.5 mg/kg q 4 hrs IV. Buprenorphine may be given at 0.02-0.10 mg/kg SQ or IV. It is best to discharge the patient to the owner as soon as is medically feasible to decrease the pa-tient’s stress associated with hospitalization.
Specific Species Considerations
Rabbits are prone to developing adhesions after abdominal surgery compared with carnivores. They are more like horses and human, and they are used as an experimental model for preventing and treating adhesions. Careful technique and gentle tissue handling are vital to prevent adhe-sions from forming. The use of calcium channel blocking agents (verapamil) and non-steroidal anti-inflammatory drugs have been used to prevent adhesion formation. It is also preferred to use suture material that is absorbed by the action of hydrolysis rather than proteolysis. Hemos-tatic clips are very useful for controlling hemorrhage from vessels within the abdominal cavity.
The primary indication for gastrotomy is removal of a foreign body. Rabbits are not able to vo-mit due to the cardia and the stomach. The pylorus is easily compressed by the stomach because it exits at a sharp angle. While the presence of a trichobezoar is considered normal, on occasion, a small chuck can break off and obstruct the pylorus or proximal duodenum resulting in severe, acute gastric dilation. Carpet fiber seems to be the most common GI foreign body in house rab-bits. Rabbits with a GI foreign body can present with clinical signs similar to those observed in rabbits with GI ileus and it can be difficult to differentiate the two. Also, these can occur simul-taneously. A GI foreign body obstruction usually causes a more acute and severe presentation than does GI ileus. The acute distention of the stomach with gas and fluid, the inability to vomit, and the poor tolerance to the pain associated with the distention make this problem a rapidly life-threatening condition in rabbits. Rabbits with a foreign body obstruction present with acute de-pression, abdominal distention, and are much more systemically ill than rabbits with GI ileus.
It is generally considered best to stabilize the patient prior to surgery; however, the rapid decline of rabbits with GI obstruction make the prognosis guarded to poor, at best. Pathophysiological-ly, rabbits with pyloric or proximal duodenal obstruction undergo changes similar to those seen in dogs with gastric dilatation and volvulus. It is vital to decompress the stomach as quickly as possible and prevent it from distending while other treatments are initiated. It is difficult to pass an orogastric tube in many conscious rabbits and the size is often small enough that the lumen plugs rapidly with ingesta. Similarly with nasogastric tubes, gas may be removed but the ingesta in the stomach often plugs the tube quickly. In many patients, trocharization with a large bore needle or catheter is needed. The procedure may need to be repeated as the lumen of the needle may also plug. In some cases, an emergency gastrostomy tube placement may be done with a local anesthetic to allow continued decompression of the stomach so the patient can be stabilized before going in to relieve the obstruction.
The incision is made from the sternum to the pubis to allow examination of the entire gastroin-testinal tract. Laparotomy sponges are used to pack off the stomach to prevent contamination of the peritoneal cavity. The gastrotomy incision is made in avascular region half way between the greater and lesser curvatures. A variety of sizes of sterile spoons should be available to assist in removing the object. Following removal of the foreign body, the stomach should be irrigated and suctioned. The gastric mucosa should be evaluated for any evidence of ulcers and the pylo-rus should be evaluated for patency. A 2 layer inverting closure using a synthetic, monofilament, absorbable suture is recommended. The first layer is a simple continuous in the submucosa and mucosa. Technically it is best if the suture penetrates the submucosa, but not the mucosa of the stomach, as the rabbit’s gastric pH (1.25-1.5) is lower than that of dogs and cats and may prema-turely weaken the suture. The second layer is an inverting pattern such as a Cushing to provide serosa-serosa contact for faster healing. The liver should be closely evaluated and biopsy taken if its appearance is abnormal (pale or yellow) to assess for hepatic lipidosis.
Postoperative management is critical. Therapy as described above is instituted including naso-gastric tube for alimentation and hydration, intravenous fluid support, metoclopramide or cisa-pride to increase gastric emptying and GI motility, and a high fiber diet. Once the patient is eat-ing on its own it may be discharged.
Enterotomy and Intestinal Resection and Anastamosis (IRA)
Enterotomy or intestinal resection is most often indicated in rabbits with foreign body ingestion. Care is taken not to damage the cecum. Enterotomy or intestinal resection is performed similarly to other small animals. Longitudinal incisions and transverse closures are sometimes used if the luminal diameter is too small. Closure is usually appositional suture technique with 4-0 to 6-0 synthetic monofilament suture.
Removal of calcium carbonate sludge or stones is probably the most common indication for cys-totomy in rabbits. Rabbits excrete excess dietary calcium as calcium carbonate through the kid-neys. This material may accumulate in the urinary bladder. In some cases, this sludge like material can be removed using fluid diuresis and manual expression. Occasionally, this material becomes firm enough that it will not pass or it may actually form a stone. This may then cause an obstruction. Other indications for cystotomy include neoplasia, diseases that require histologic evaluation of the urinary bladder, or for evaluation of the patency of the ureters.
The fraction excretion of calcium is less than 2% in most mammals, whereas the range for rabbits is 45-60% (20-30 times greater than in dogs and cats). This material looks like chalk in the urine. It is usually passed in the urine. Sometimes it accumulates in the bladder and forms a sludge-like material that is not excreted during urination. In some rabbits, cystic calculi of calcium carbonate form. These calcium carbonate crystals are often noted on radiographs or sonograms as an incidental finding. Clinical signs of problems associated with calcium carbonate urolithiasis include stranguria, pollakiuria, anorexia, and decreased stool production. If there is lower urinary tract obstruction, signs can be more serious and include lethargy and depression.
Cytotomy in rabbits is analogous to that in other species. The bladder is exposed through a caud-al ventral midline approach and isolated using moist sponges. Stay sutures are placed around the area of the proposed cystotomy incision. An incision is made on the ventral aspect of the bladder in a relatively avascular region. The stones or sludge are removed and the bladder irrigated to remove all calcium carbonate. A tom cat catheter is inserted into the neck of the bladder and sa-line irrigated to assure patency of the urethra. The bladder wall is closed with a simple inter-rupted pattern of 4-0 monofilament synthetic absorbable material. While the submucosa is the holding layer and some sources recommend that sutures not penetrate the mucosa, this is techni-cally difficult. Therefore, full thickness suture bites are placed.
The short term prognosis for rabbits requiring cystotomy for calcium carbonate crystaluria is good. Unfortunately, recurrence is common as the cause has not been established. Many recom-mend these rabbits receive grass hay rather than alfalfa because it is lower in calcium and reduce the amount of pellets given. Acidifiers are not effective because rabbits are herbivores with na-turally alkaline urine.
Rabbits form thick-walled abscesses that contain a caseous purulent discharge in reaction to most bacterial infection. Staphylococcus aureus, Pasturella multocida, Pseudomonas aeruginosa, Proteus species, and Bacteroides species are the most common isolates from subcutaneous ab-scesses in rabbits. Affected animals are presented with a non-painful swelling with no associated clinical signs. Abscesses in rabbits are simple to diagnose but difficult to treat. Recurrence is common if this is managed with simple lancing and drainage. Abscesses should be excised with substantial margin so that all contaminated tissue is removed. Hemostasis should be controlled with suture or hemoclips and close the skin with surgical staples. Long-term antibiotic therapy may be necessary following surgical excision.
Dermoplasty and Tail Amputation
Dermatologic problems that result from urine scald or chronic diarrhea are common in pet rabbits. Urine scald occurs when the rabbit's skin, especially around the urethra and between the hind legs remains damp with urine. This leads to moist dermatitis.bbIt may occur as a result of obesity, arthritis, or urinary tract disease. Skin around the urethra, between the hind legs, and sometimes the hock is inflamed and erythematous. The hair in the area is continually damp.
Moist dermatitis is usually managed medically. The hair is shaved from the affected area, which is then cleaned and allowed to dry. Topical products such as Desitin® or Domeboro Powder (Bayer Inc., Elkhart, IN) are often applied. Underlying causes for the condition need to be treated as well. This tends to be an ongoing problem, so owners should monitor their affected rabbits closely for signs of recurrence. In cases where medical management is unsuccessful, dermoplasty and/or tail amputation may help. Dermoplasty of the caudal abdomen allows removal of the fold of skin that interferes with the passage of urine. A combination of tail amputation and dermoplasty to lift the genital area dorsally results in passage of urine in a more caudal direction. These surgeries are adjunct and salvage procedures. Every effort should be made to correct the underlying problem before surgery is undertaken.
Published on December 3, 2007.