Rabbit GI Case Challenge Discussion

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Introduction

Gastrointestinal disorders are common in rabbits. Most gastrointestinal obstructions are located in the pylorus, upper duodenum, mid-duodenum, or less commonly the ileocecocolic junction, as these are the narrowest regions of the rabbit gastrointestinal tract. In rare cases, obstruction involves the cecum (Schumann 2014, Oglesbee 2012).

 

Pathogenesis

The most common cause of obstruction is a mat of compressed fur hair (Schumann 2014, Oglesbee 2012, Meredith 2008, Harcourt-Brown 2007). This trichobezoar is theorized to be all that remains after a fur-filled cecotroph is ingested during normal cecotrophy (Oglesbee 2012, Harcourt-Brown FM 2007, Harcourt-Brown TR 2007). Long-haired rabbits or individuals housed with long-haired breeds are at increased risk due to social grooming (Mondal 2006). Other potential causes of gastrointestinal obstruction include a dried clump of ingesta or foreign bodies such as carpet, cloth fibers, rubber, or plastic. Locust bean seeds have also been implicated as a cause of intestinal blockage (Harcourt-Brown FM 2007, Harcourt-Brown TR 2007). In rare instances, obstruction can develop secondary to post-operative adhesions or mass lesion such as a tumor, abscess, or tapeworm cyst (Oglesbee 2012, Harcourt-Brown FM 2007, Harcourt-Brown TR 2007). Strangulations, intussusceptions, and diverticulitis have also been described (Harcourt-Brown TR 2007, Weisbroth 1975).

The normal rabbit stomach possesses a very tight, very well-developed cardiac (or upper esophageal) sphincter that prevents vomiting or even eructation. The outflow tract of the normal rabbit stomach also has a particularly acute angle (Oglesbee 2012, Meredith 2008). Unfortunately these anatomic features can quickly prove disastrous if gastric outflow becomes blocked, even briefly. The large amounts of saliva and gastric secretions normally produced by the rabbit can rapidly cause gastric dilatation. The distended stomach further compresses the sharp angle of the pyloric outflow tract creating a vicious cycle of distension and obstruction (Oglesbee 2012, Meredith 2008). Fluid that accumulates within the stomach can also undergo fermentation to produce large volumes of gas, worsening bloat (Oglesbee 2012). High intragastric pressure and the severely dilated stomach can place excess pressure on the diaphragm, compressing the relatively small lung volume of the rabbit and putting the patient at risk for respiratory failure with respiratory acidosis. Other potential effects of bloat and obstruction include: marked increases in intestinal bacteria and their toxins, mechanical occlusion of the vena cava resulting in decreased venous return to the right side of the heart, reductions in cardiac output and blood pressure, and metabolic acidosis (Schumann 2014).

 

History

Obstructed rabbits are acutely ill (Schumann 2014). Anorexia and depression are the chief complaints (Oglesbee 2012). Fecal pellet production suddenly stops in affected rabbits, and unlike rabbits afflicted with hypomotility or ileus, there is no history of a recent stressful or painful event. Dietary history may also be unremarkable (Meredith 2008).

 

Physical exam findings

If evaluated early, the rabbit is often quiet, alert and responsive. Tachypnea and tachycardia are observed. As disease progresses and metabolic derangements and shock develop, the patient becomes depressed or minimally responsive to external stimuli (obtunded), severely dehydrated, hypotensive (< 90 mmHg), and bradycardic (< 130-180 bpm) (Huynh 2013, Hedley 2011, Meredith 2008). The patient may even present in lateral recumbency and a large, fluid-filled or tympanic stomach is often palpable caudomedial to the last rib (Oglesbee 2012, Harcourt-Brown TR 2007). Most rabbits exhibit signs of severe abdominal pain such as immobility, hunched posture or lying down in a stretched-out position, and tooth grinding or bruxism (Schumann 2014). Obstructed rabbits are often hypothermic (< 98°F or 36.7°C) while most stasis rabbits are normothermic (Schumann 2014, Huynh 2013, Oglesbee 2012, Meredith 2008). If the condition continues, the patient can die from hypovolemic shock and electrolyte/acid-base imbalances or from peritonitis after the gastrointestinal tract ruptures (Schumann 2014, Oglesbee 2013, Meredith 2008). In severe cases, death can occur within 8 hours from the onset of clinical signs (Harcourt-Brown TR 2007).

 

Minimum database

The complete blood count is often unremarkable. Anemia, panleukopenia, or thrombocytopenia can be observed when there is gastrointestinal blood loss due to ulceration or perforation (Ritzman 2014).

Biochemistry panel results may indicate dehydration and a variety of acid-base and electrolyte disorders (Oglesbee 2012). The clinical significance of high lactate levels in the rabbit with bloat and gastrointestinal obstruction is unknown (Hunyh 2013). Harcourt-Brown (2012) has described a significant relationship between blood glucose and severity of clinical disease. Rabbits showing signs of stress had higher blood glucose than rabbits showing no signs of stress. Rabbits with total anorexia also displayed higher blood glucose values than those eating normally or with partial anorexia. Severe hyperglycemia (> 360 mg/dL or 20 mmol/l) was associated with conditions that carry a poor prognosis. Rabbits with confirmed intestinal obstruction had a mean blood glucose of 445 mg/dL (24.7 mmol/l) (n=18). This was significantly higher than rabbits with confirmed gastrointestinal stasis, which had a mean value of 153 mg/dL (8.5 mmol/l) (n=51).

Survey radiographs are helpful in distinguishing between gastrointestinal obstruction and gastrointestinal hypomotility or ileus. Outflow obstruction may be indicated if the stomach is distended (Ritzman 2014). The stomach can appear severely distended with gas, fluid, or both (Oglesbee 2012). The bubbles of gas within the stomach should not be confused with the halo of gas sometimes seen with ileus. Gaseous distension of intestinal loops proximal to the obstruction is sometimes observed within the mid-duodenum or ileocecocolic junction. Pneumoperitoneum suggests rupture of the stomach or intestinal tract (Oglesbee 2012, Meredith 2008).

Sonography or serial radiographs can be used to further elucidate the obstruction or when the results of survey radiographs are equivocal. Serial radiographs can also document patient response to urgent care measures. If the obstruction passes through the ileocecocolic junction, gas will become visible in the cecum and more gas-filled intestinal loops are also seen radiographically.

Contrast studies are rarely useful for emergent cases because the normal gastrointestinal transit time is relatively slow in rabbits. If utilized, select a water-soluble contrast medium and proceed with caution as the bloated stomach is at risk for rupture due to the risk of focal mucosal necrosis from extreme distension. Consider first emptying the stomach with the help of a stomach tube to reduce the risk of complications (see urgent care below).

 

Differentials

Unfortunately gastrointestinal obstruction is not uncommon in the pet rabbit. This condition must be distinguished from non-obstructive gastrointestinal (GI) hypomotility or ileus (Table 1). The onset of clinical signs is acute with obstruction (over 24-48 hours) and more gradual or insidious with GI stasis (days to weeks). On survey radiographs of obstruction, the stomach is classically distended with fluid and/or air. In GI stasis, the stomach is usually the last segment of the gastrointestinal tract to become distended (Meredith 2008).

Table 1. Differentiation of obstructive and non-obstructive gastrointestinal disease in the rabbit (Meredith 2008)
	Obstructive	Non-obstructive
Clinical signs	Acute onset (24-48 hours)	Gradual onset (days, weeks)
	Fecal output halts suddenly	Gradual reduction in fecal output and size
Exam findings	Quiet early >> profound depression	Alert and responsive early >> gradual onset of depression
	Severe dehydration	Mild to moderate dehydration
	Abdominal pain
	Reluctance to move
	± Signs of shock
Radiographic findings	Fluid and gas observed cranial to obstruction	As disease progresses, gas can fill entire GIT, stomach usually last to distend
		Fluid only present late in disease process
	Bubbles of gas in stomach, not halo	Often a halo of gas surrounds compacted material
	If cecum obstructed, fluid and bubbles of air seen within cecum	Compacted material in stomach and sometimes cecum
GIT: gastrointestinal tract

Other causes of gastric dilation include mucoid enteropathy and dysautonomia (Varga 2014).

 

 

Key points of urgent care

Gastrointestinal obstruction can rapidly become life threatening if left untreated, and rabbits often present severely compromised and extremely painful. This condition is considered a surgical emergency and initial treatment goals strive to stabilize the patient through analgesia, decompression when indicated,, and supportive care (Schumann 2014, Oglesbee 2012, Harcourt-Brown 2007). Cautiously, yet aggressively warm the hypothermic patient.

 

Fluid therapy

Use fluid therapy to treat shock when present and correct fluid and electrolyte imbalances. Subcutaneous fluids may be sufficient for rabbits with early disease, but intravenous catheter placement is often indicated (Oglesbee 2012).

 

Analgesia

Buprenorphine (0.02-0.05 mg/kg SC, IV q 6-12h) is a popular choice to manage pain (Oglesbee 2012). Although there is potential for opioids to slow gastrointestinal motility, this is infrequently noted in most exotic companion mammals (Ritzman 2014). Non-steroidal anti-inflammatory drugs (NSAIDs) such as meloxicam should be administered only to well-hydrated patients. Further, the use of NSAIDs as a pre-anesthetic drug in the critically ill small mammal (in which blood pressure is not monitored) carries some controversy (Ritzman 2014).

 

Decompression

Orogastric intubation is indicated to decompress the moderately or severely distended stomach (Huynh 2013, Harcourt-Brown TR 2007, Bourne). There are several potential complications. If the rabbit chews the tube, it can inhale or swallow a foreign body. It is also possible to traumatize the larynx or even pass the tube into the trachea causing breathing difficulties or aspiration pneumonia (Varga 2014, Bourne).

Despite the difficulty of endotracheal intubation in anaesthetized rabbits it is surprisingly easy to pass a stomach tube into the trachea. Selection of a large tube should prevent this happening…—Molly Varga, Textbook of Rabbit Medicine (2014)

 

Equipment needed (Bourne):

• 16- or 18-Fr red rubber catheter – Additional fenestrations may be needed to allow larger volumes to pass.

• Mouth gag or speculum to prevent the rabbit from chewing through tubing, such as a piece of wood with a hole drilled through the middle

The tube can be passed…without a gag, if the mouth is gently held closed so the rabbit cannot chew –TR Harcourt-Brown (2007)

• Water-soluble lubricant
• Syringe
• + Stopcock
• + Sedation or general inhalant anesthesia – Patients are usually moribund but can be sedated (midazolam 0.5-1.0 mg/kg IM, IV) or anesthetized with isoflurane or sevoflurane as needed. An endotracheal tube should ideally be in place during the procedure.

To pass an orogastric tube, place the anesthetized or moribund patient in left lateral recumbency. Maintain others in sternal recumbency. Measure the distance from the nose to last rib (distance to stomach), then mark and lubricate the tube. Place the mouth gag in the diastema and pass the tube over the tongue and into the esophagus. Minimal force should be used to pass the tube, although slight resistance may be appreciated as the tube passes through the upper esophageal sphincter (Harcourt-Brown TR 2007). After placing the tube, monitor respirations for a few seconds and assess mucous membrane color.

Once the tube is in the stomach, high intragastric pressure can force some gas or fluid out of the stomach, however further decompression requires gentle massage of the stomach. Although the tube can become clogged, remove as much fluid and gas as possible. Difficult cases may require light suction and intermittent retropulsion (Harcourt-Brown TR 2007). Afterwards, gently remove the tube unless the rabbit will immediately go into surgery (Varga 2014, Oglesbee 2012, Bourne).

Nasogastric intubation to relieve tympany has also been described (Huynh 2013). Although tempting, percutaneous trocharization is not recommended as there is significant risk of gastric rupture (Oglesbee 2012).

 

Monitoring

Monitor rabbits receiving supportive care and decompression closely (Table 2). Depending on the underlying cause of obstruction, it is possible for the blockage to resolve with medical management alone (Oglesbee 2012, Meredith 2008). Palpate the abdomen and auscult gut sounds frequently. Repeat survey radiographs as needed to see if changes in the gas pattern suggest movement of the gastrointestinal tract and monitor the patient for production of formed fecal balls, ideally in moderate to large amounts (Ritzman 2014).

 

Table 2. Parameters to monitor in the rabbit with gastrointestinal obstruction

Abdominal palpation Gut sounds Serial survey radiographs Eliminations

 

As clinical signs improve, the rabbit should begin to eat, drink and seem more comfortable. If the condition has not resolved within a short period of time surgical intervention is indicated. A monitoring period of approximately 2-6 hours may be appropriate when clinical status allows.

 

 

Case management

Surgery

If the obstruction is not moving, as determined by clinical signs and serial radiographs, then the case becomes surgical and an exploratory laparotomy is indicated. As a general rule, rabbits do not tolerate gastrointestinal surgery as well as other species and high complication rates of up to 50% have been described (Harcourt-Brown FM 2007). Many patients die during surgery or within 48 hours after surgery from peritonitis, endotoxemia, acute renal failure, and/or severe post-operative gastrointestinal stasis (Oglesbee 2012).

The abdomen is carefully opened with a midline incision from sternum to umbilicus. Inspect the retroperitoneal space for fluid and ingesta that might indicate peritonitis or gastric rupture. Gently palpate the stomach for the presence of foreign material (Harcourt-Brown TR 2007). An intestinal obstruction can often be identified by following gas-filled intestinal loops to the blockage (Varga 2014). Remember the proximal duodenum is the most common site of obstruction. Carefully inspect the obstruction site for evidence of devitalization or any pathology that could increase the risk of obstruction (Harcourt-Brown TR 2007). When an intestinal foreign body is identified, gently manipulate the material into the stomach whenever possible. Gastrotomy is better tolerated with a lower risk of post-operative complications (Oglesbee 2012). The rabbit intestinal tract is relatively thin-walled and there is increased risk of stricture, leakage or ileus with enterotomy when compared to gastrotomy (Harcourt-Brown FM 2007). Alternatively a more distal foreign body can be carefully milked through the ileocolic valve and into the hindgut (Harcourt-Brown TR 2007). If an enterotomy is necessary, carefully incise the anti-mesenteric border distal to the foreign body and close the incision with fine (4-0 to 6-0) monofilament suture. Carefully check the enterotomy site for leakage. Omentalization is usually not feasible due the relatively small rabbit omentum (Varga 2014, Harcourt-Brown TR 2007). If no gastrointestinal foreign body is found, explore the abdomen for evidence of other potential causes like neoplasia, abscess, or adhesions.

Rabbits are prone to develop post-surgical adhesions so consider the use of verapamil (200 μg/kg PO q 8h for 9 doses) or carboxymethylcellulose to minimize the risk (Meredith 2008).

 

Post-operative period

Continue supportive care postoperatively including nutritional support, fluid therapy, and pain management (Oglesbee 2012). Meloxicam can be used in the stable and hydrated small mammal patient when they begin eating (Ritzman 2014). Prokinetic medications, such as metoclopramide (0.5 mg/kg PO, SC, IM q6-8h), cisapride (0.5 mg/kg PO q8-12h), and ranitidine (2-5 mg/kg PO q12h), are also frequently used (Ritzman 2014, Oglesbee 2012, Hedley 2011). Cisapride is more potent, with broader prokinetic activity than metoclopramide, however the manufacturer has voluntarily placed cisapride under a limited-access program as a result of arrhythmias and deaths reported in human patients. This drug must be obtained for veterinary patients through compounding veterinary pharmacies in the US (Ritzman 2014). In the UK, access to cisapride requires a Special Treatment Certificate from the Veterinary Medicines Directorate (Hedley 2011). Domperiodone (0.5 mg/kg PO q12h) has recently shown promise as a prokinetic in rabbits (Hedley 2011), however like cisapride this drug has been associated with increased risk of cardiac death in human patients (Hondeghem 2013).

 

Homecare recommendations

Instruct owners to monitor patient appetite, attitude, activity, and eliminations. Anorexia, absence of fecal droppings, diarrhea, and blood or mucus in the stool, limited movement or reluctance to move, liquid or sloshing abdominal sounds, and/or abdominal swelling or soreness are all cause for alarm. The rabbit should be evaluated as soon as possible if any of these signs are observed (Ritzman 2014).

 

If surgery is not possible…

If surgery not possible for financial or clinical reasons, Schumann (2014) has described the successful medical management of gastric dilatation cases (diagnosed via clinical signs and survey radiographs) with a combination of prokinetic drug (metoclopramide 0.5 mg/kg SC TID), analgesia (metamizole 50 mg/kg SC TID), and crystalloid fluids (25 ml/kg plus deficits BID SC). After 30-60 minutes of stabilization the animals were started on nutritional support and supplemental heat was provided as needed. Medical treatment was successful in 130 cases (89%) with a mean treatment time of 3 days. For obvious reasons, prokinetics are generally contraindicated prior to surgery and the risk involved in this clinical decision should be thoroughly discussed with the owner (Meredith 2008). Any delay before surgery is generally expected to reduce the chance of survival (Schumann 2014).

 

 

Prognosis

There is a good chance of recovery when gastrointestinal obstruction is diagnosed early, however as the condition progresses the rabbit will decline quickly and therefore the prognosis is often guarded (Oglesbee 2012).

 

 

Prevention

Review the rabbit’s diet and particularly dietary fiber levels. The adult pet rabbit diet should maximum hay and minimize pellets. Regular grooming may also reduce the risk of obstruction and some clinicians recommend regular clipping of long-haired breeds, particularly individuals that have suffered from bloat (Schumann 2014). If gastrointestinal obstruction recurs, more in-depth diagnostics such as ultrasound or contrast radiography is indicated to look for underlying mechanical defects like neoplasia.

 

 

Summary

Gastric dilatation or “bloat” and gastrointestinal obstruction is an acute and life-threatening condition of pet rabbits commonly caused by an obstruction with pellets of compressed hair. Presentation and clinical signs of gastrointestinal disease in rabbits are often non-specific and this emergency condition can sometimes be difficult to distinguish from non-obstructive disease or gastrointestinal ileus. Laboratory tests, always nice to have before surgery, are not always helpful in distinguishing stasis from obstruction, although severe hyperglycemia may be suggestive. Fortunately the radiographic appearance of a rabbit with acute gastrointestinal obstruction differs greatly from that of a normal rabbit or a rabbit with gastrointestinal hypomotility. Radiographically, the stomach is filled with gas and/or fluid and ingesta with upper gastrointestinal obstruction. Dilated loops of bowel may also be visible proximal to the obstruction. Surgery is generally considered the treatment of choice.

Visit LafeberVet’s handout Bloat and Gastrointestinal Blockage in Rabbits for helpful client education.

 

References and further reading