19 Sep International Rabbit Day: Abdominal Surgeries in Rabbits

STAT ABDOMINAL SURGERIES IN RABBITS

Lauren V Powers, DVM, DABVP (Avian Practice), DABVP (Exotic Companion Mammal Practice)
Avian and Exotic Pet Service
Carolina Veterinary Specialists
Huntersville, North Carolina

INTRODUCTION

The exotic companion mammal practitioner is occasionally presented with rabbits (Oryctolagus cuniculus) that may require immediate surgical intervention for acute abdominal disease. Liver lobe torsion, intestinal obstruction, inguinal urinary bladder herniation, and endometrial venous aneurysm are some of the diseases that may warrant a rapid diagnosis and surgical intervention for a successful clinical outcome.

CLINICAL PRESENTATION

Rabbits with acute abdominal diseases often experience severe pain. Scoring systems for pain in rabbits have not yet been developed, but several studies have investigated methods of evaluating rabbits for pain.1,2 Signs of pain in rabbits can be quite subtle to the average observer, even for rabbits experiencing extreme pain. Clinical signs of acute pain in rabbits include anorexia, decreased fecal production, lethargy, reluctance to move, hunched body position, tooth grinding, increased respiratory rate, and defensive aggression. Behaviors and postures in rabbits postoperative for ovariohysterectomy include back arching, skin twitches on the back, contraction of the abdominal muscles, and belly pressing.2 These abnormal behaviors and postures may be missed by many observers.2 Changes in facial expression due to pain such as grimace can be subtle in rabbits.2 The physical examination should include assessment of rectal temperature, hydration status, heart rate and rhythm, mucus membrane color and capillary refill time, and pain score. Low rectal temperature was a major predictor of fatal outcome for 316 hospitalized rabbits in a recent prospective cohort study.3 Older age, presence of systemic disease, and gastrointestinal stasis were also significantly associated with increased risk of death.3 Four quadrant abdominal auscultation for borborygmus should be performed. Abdominal palpation may reveal gastric distension with fluid or gas or an empty stomach, cecal dilation or contraction, and abdominal masses.

DIAGNOSTICS

A minimum data base should be obtained for rabbits undergoing surgical procedures, such as measurement of the packed cell volume and total solids (PCV/TS), glucose, BUN, and creatinine. Full hematology and biochemical testing is preferred when possible.4 A complete urinalysis should be performed for rabbits with urogenital disorders.

Radiography

Survey radiographs can be helpful for the diagnosis of abdominal disorders in rabbits. The presence of a large, fluid or gas filled stomach in a rabbit that has not eaten in several days is suggestive of GI stasis and ileus or obstruction.5 Gaseous dilation of the small intestines can be seen with ileus and mechanical obstructive disease. Gastrointestinal stasis and ileus can be challenging to differentiate from intestinal obstruction using plain survey radiography. Contrast radiography (eg. upper GI contrast radiography, colonography) may be helpful to further assess rabbits for obstructive GI disease.6

Ultrasonography

Abdominal ultrasound is a sensitive and noninvasive diagnostic modality for the detection of acute abdominal pathology despite the presence of significant amounts of interfering ingesta and gas in normal rabbits. Abnormal ultrasonographic findings include free peritoneal fluid, organomegaly, GI obstruction, organ torsion (eg. hepatic lobe torsion, uterine torsion), and abdominal masses.6,7

SELECTED DISEASES

Gastrointestinal

Stasis and Ileus

Because gastric stasis and ileus generally responds well to aggressive medical therapy and since exploratory surgery carries significant risks in rabbits, surgical intervention is generally contraindicated.5,8 Surgery is indicated for known or strongly suspected foreign body ingestion and obstruction and for rabbits who fail to respond to medical therapy after roughly three to five days.4,5 A thorough working knowledge of the rabbit gastrointestinal anatomy is absolutely essential for a positive surgical outcome.9
Care must be taken not to damage the cecum during the initial surgical approach.5 For the rabbit gastrotomy, an incision is made in the avascular area between the greater and lesser curvatures.5

Enterotomy or intestinal resection and anastomosis may be indicated for intestinal foreign bodies (eg. trichobezoars), adhesions and strictures, mesenteric abscesses, intussusceptions, and neoplasia.4,5,10,11 In a retrospective study of 76 rabbits with gastric dilation, intestinal obstruction was observed in 64 animals, 49 of which were obstructed with fecal pellets comprised of re-ingested, compressed hair.11 Other causes of intestinal obstruction in this study included ingested locust bean seeds, neoplasia, postspay adhesions, ingested carpet fibers, tapeworm cysts, and strangulated hernia.11 For the 40 rabbits that underwent abdominal exploratory surgery in this study, ten (25%) died intraoperatively, three (7%) were euthanized due to intestinal neoplasia, eight (20%) died postoperatively, and 19 (48%) made a full surgical recovery.11 Surgery of the colon is primarily performed for obstructions at the fusus coli.5 The surgical approach to the fusus coli at the root of the mesentery is challenging at best.5

Liver Lobe Torsion

Hepatic lobe torsion has been reported in rabbits and is associated with acute abdomen.7 Clinical signs in a recent retrospective case series of 16 rabbits included anorexia, lethargy, and decreased fecal production.7 Anemia, red blood cell fragmentation, and elevated hepatic enzyme activities were common in this study.7 Abdominal radiographs revealed nonspecific abnormalities such as rounded hepatic margins or hepatomegaly, and increased gastric or intestinal gas suggestive of GI stasis or obstruction.
Abdominal ultrasonography was diagnostic for all cases.7 Ultrasonographic findings included hepatomegaly, rounded lobar margins, free peritoneal fluid, and reduced or absent blood flow of the affected liver lobe.7 The caudate lobe was most commonly affected, followed by the right lateral lobe, left lateral lobe, and right medial lobe.7 Hepatic lobectomy was performed in nine cases, all of which survived surgery in this report.7

Urogenital

Adhesions

Rabbits are highly prone to adhesion formation from abdominal surgeries such as ovariohysterectomy.4,5,6 In a retrospective case study of 76 rabbits with gastric dilation and intestinal obstruction, two rabbits had post-spay adhesions as the cause for the intestinal obstruction.11 Colonic obstruction in two pet rabbits due to adhesions from the transected uterine body was reported in a recent case series of three rabbits.6 Meticulous technique should be used during abdominal surgery in rabbits.6 When possible, the transected portions of the reproductive tract such as the uterine body and vagina should be oversewn with an inverting pattern and the parietal peritoneal membrane should be reapposed during abdominal incision closure. Absorbable suture should always be used for abdominal surgeries in rabbits, as adhesion formation and fistulous tracts have been reported for nonabsorbable intra-abdominal materials.

Urinary Bladder Herniation

Herniation of the urinary bladder has been reported in the rabbit and can be a cause of acute abdomen.12,13,14 In one report, a 4-month-old intact female rabbit was presented with a history of lethargy, anorexia, diarrhea, and a subcutaneous mass in the inguinal region.12 Survey radiography, excretory urography, and fluid analysis were used for the diagnosis. The hernia was successfully surgically repaired by replacement of the urinary bladder and inguinal herniorrhaphy.12 In a separate report, an 8- year-old intact male rabbit was presented with unilateral scrotal swelling. Radiography, ultrasonography, and cytology were useful for the diagnosis. The rabbit underwent successful inguinal herniorrhaphy and castration.13 In a case series of six intact male rabbits between four and eight years of age with fluctuant scrotal and/or inguinal swelling, inguinal herniorrhaphy was performed in all cases with a successful outcome in four of the six rabbits.14
Endometrial venous aneurysms (EVA) can result in life-threatening hematuria in rabbits.15,16,17 Multiple blood-filled endometrial varices (veins) periodically rupture into the uterine lumen, resulting in hematuria.18 Cylindrical blood clots formed within the uterine horn are occasionally passed and are highly suggestive of the disease.18 Since the vagina can normally store relatively large amounts of urine, the blood can be diluted with urine and appear to be arising from the urinary bladder. Red urine can be associated with porphyrin pigments that can be mistaken for blood.18 Ovariohysterectomy should be performed as soon as the rabbit is stable.18

Other

Other urogenital diseases can be associated with acute abdominal pain and warrant rapid surgical intervention, such as uterine adenocarcinoma, pyometra, dystocia, uterine torsion, and bladder calculi.18 Uterine torsion is a rare but serious condition that has been reported in the rabbit and is often associated with hydrometra, endometritis, and pregnancy.18 Bladder stones often become quite large before rabbits develop clinical signs associated with disease and emergency surgery is usually not necessary for this
condition.

PATIENT CARE

Ideally, patients should be stabilized prior to surgical intervention. Fluid therapy should be initiated prior to surgery and continued postoperatively.4,5 Intravenous catheterization and IV fluid therapy are strongly advised.4 Balanced electrolyte solutions and hydroxyethyl starch are most often used for fluid resuscitation in rabbits.

Rabbits with acute abdominal disease are often subject to severe stress and pain and should be treated with aggressive analgesic and anxiolytic therapy.4,5,19 Midazolam (0.10 to 0.50 mg/kg SQ, IM, or IV) is an excellent sedative and anxiolytic in rabbits. Analgesics commonly used in rabbits include buprenorphine (0.01 to 0.05 mg/kg SC, IM, IV), hydromorphone (0.08 to 0.20 mg/kg SQ, IM, or IV), butorphanol (0.1 to 0.5 mg/kg SQ, IM, or IV), and morphine (2 to 5 mg/kg SQ, IM, or IV).19 Adverse effects of opioid drugs on GI motility are rare in rabbits and should not be a reason to avoid their use.

Non-steroidal anti-inflammatory drugs are best avoided during the initial treatment phase for rabbits with acute abdomen due to concerns for reduced renal blood flow and the risks for GI ulceration, but are appropriate to consider for postoperative pain management once the rabbit is stable. Appropriate perioperative antibiotic therapy is often indicated for acute abdominal diseases in rabbits.4 Postoperative gastrointestinal supportive drugs such as H2 receptor antagonists (eg. ranitidine) and prokinetics (eg.
raniditine, metoclopramide, cisapride) can also be used to improve postoperative GI motility.4 Rabbits should be provided nutritional support during the postoperative period, which may include periodic assist feedings of homemade or commercially available enteral diets for small exotic mammals.5