Introduction

Gastrointestinal stasis is a common syndrome in pet rabbits and is characterized by anorexia, lack of fecal production, a large/doughy stomach, gastrointestinal pain, and tympanism in some cases. It is not a disease in itself, but rather a functional ileus associated with a myriad of potential causes, the most common being dietary issues (lack of fibers), dental disease, gastrointestinal diseases, dysbiosis, urolithiasis, liver lobe torsion, encephalitozoonosis, otitis, and any other disease leading to dysorexia. The pathogenesis of gastric stasis is beyond the scope of this presentation, which will mainly discuss its medical management. A major conundrum in these clinical situations is determining whether surgical intervention is necessary, especially to relieve a gastrointestinal obstruction. Diagnosing gastrointestinal obstructions is challenging in rabbits, as severe medical functional ileus may be hard to differentiate from mechanical ileus and extrapolating from dog and cat medicine frequently leads to unnecessary surgeries. The author’s experience and opinion are that, while gastrointestinal obstructions do occur in rabbits, the vast majority of gastrointestinal stasis cases are medical in nature. The minority of cases that are surgical include the occasional gastrointestinal obstruction and non-gastrointestinal surgical cases such as urolithiasis and liver lobe torsion. Advanced treatment options and management for medical cases are not well summarized in the literature overall. The author has also found that nasogastric tubes, while frequently advocated in the literature, are seldom necessary in the management of this condition.

We propose to go through the standard medical management process of these cases by first discussing initial assessment and stabilization followed by diagnosis of underlying causes and finishing with treatment across various severities.

Step 1: Initial Assessment and Stabilization

Any rabbit presented for gastrointestinal stasis and anorexia should at least get an initial database that will allow an evaluation of the severity of the presentation and the need for more aggressive therapy. First, in addition to determining hydration status, the volemia and perfusion status should be estimated. An indirect blood pressure measurement should be performed. It is reliable to diagnose hypotension in rabbits with Doppler measurements <80 mm Hg or oscillometric measurements <60 mm Hg (for MAP). A general idea of the perfusion status of the patient may be acquired by assessing the femoral pulse, heart rate, capillary refilling time, and body temperature (cold when hypotensive). Urinary specific gravity should also be obtained if possible. Finally, a blood gas and electrolyte panel is essential in understanding acid-base disorders, assessing prognostic indicators, and devising an initial therapy plan. Blood glucose, lactates, and hematocrit (or hemoglobin) are usually also part of the standard blood gas/electrolyte panel. The i-STAT portable analyzer may be useful, but lacks a cartridge with a comprehensive panel to the author’s knowledge. When collecting blood for blood gas analysis, enough volume should be collected for a CBC/biochemistry panel. Fast ultrasound examination should also be performed to screen for free fluid and obvious masses such as T-fast and A-fast.

With this initial database, several poor prognostic indicators may be detected, which have been identified in rabbits in the scientific literature or through the author’s experience. Hypothermia (<38°C [100.4°F], for each 1°C lower, the odds of death double for all causes of mortality) is a well-known prognostic indicator in rabbits.¹ Other poor prognostic indicators include hyperglycemia (especially >20 mmol/L [360 mg/dl],² mainly associated with obstruction, but also hypotension), hypoglycemia (associated with sepsis), hypochloremic metabolic alkalosis (suggestive of obstruction), high lactate (>20 mmol/L, much higher than in domestic carnivores, especially concerning in non-struggling animals), hyponatremia (especially <129 mmol/L),² hypotension (<80 mm Hg on Doppler), and hypoxemia (PvO₂<30 mm Hg, svO₂<50%, spO₂<90–94). Detecting one or several of these values should trigger a more aggressive therapeutic approach.

In terms of treatment, the hypovolemia and hypotension absolutely need to be addressed first. If there is evidence of hypovolemic shock or sepsis, an intravenous (or IO if not possible) should be placed and fluid resuscitation started. An initial bolus of 10 ml/kg of crystalloids can be given followed by a rate of 10 ml/kg/h. Then, endpoints are reassessed (CRT, body temperature, blood pressure, mentation, urine output, blood gases, lactates). If no or minimal response is seen, a vasopressor should be added. Norepinephrine at 0.5–1 μg/kg/min is the vasopressor of choice in rabbits as dopamine has shown not to be effective in this species.^3,4 Most hypovolemic shock cases are poorly responsive to fluids alone in rabbits and norepinephrine should be used frequently, especially if sepsis is suspected (most of these patients are refractory to fluid resuscitation). Rabbits are also prone to fluid overload.

At the same time, all other homeostatic disorders should be corrected such as core body temperature (placement in an incubator or active rewarming), oxygen therapy if dyspneic, a bolus/CRI of dextrose if hypoglycemic (2.5–5% dextrose IV), a CRI of calcium if ionized hypocalcemia, bicarbonates for persistent metabolic acidosis, and pain medications. Hypoglycemia is relatively uncommon in rabbits, which tend to show the opposite trend. Therefore, dextrose administration should not be done without measuring the glycemia first. Ionized hypocalcemia is relatively uncommon in rabbits and may be caused by sepsis. Note that the ionized calcium in rabbits is much higher than in domestic carnivores (around 1.7–1.8 mmol/L), so dog and cat cut-off should not be used for triggering therapy. The use of bicarbonates is controversial. Initially, pain should be addressed with opioids such as buprenorphine SC (0.05 mg/kg at least), hydromorphone 0.1–0.3 mg/kg SC or fentanyl CRI at 3–5 μg/kg/h (more effective than buprenorphine). CPR should follow general guidelines and will not be covered here.

If sepsis is suspected (hypoglycemia, ionized hypocalcemia, fever, hypotension) or enterotoxemia (shock and liquid diarrhea), then norepinephrine should be started right away at high doses in combination with IV antibiotics (enrofloxacin/metronidazole or other combinations). A blood culture is also recommended if possible. Pasteurella multocida is a common culprit in septic cases. Toxin binders can be used in case of enterotoxemia such as Bio-sponge® (if the rabbit can swallow).

A gastric obstruction should be suspected with hypochloremic metabolic alkalosis, hyperglycemia, very large stomach (larger than for usual gastric stasis), intense pain, and regurgitation (does occur in rabbits, it is usually a bad sign). Obstruction may also be identified on abdominal ultrasound. In case of small intestinal obstruction, a hypochloremic metabolic alkalosis may not be present as the chloride is reabsorbed in the small intestines. When the rabbit is obstructed or in severe functional ileus (that will mimic obstruction), the stomach may be decompressed through passing an orogastric red rubber catheter. The patient should generally be sedated for this to facilitate placement. It may not be very rewarding as the tube frequently obstructs with stomach content.

In general, it is not recommended to force-feed unstable, dehydrated, or obstructed rabbits. Lidocaine should not be given at this stage as it has hypotensive effects in rabbits.⁵ Percutaneous gastrocentesis is never recommended and is rarely rewarding when performed.

When the patient is stabilized and the shock reversed, then protocols for maintenance therapy and comprehensive diagnostic workup should be started (see below).

Step 2: Diagnosing the Cause

Except for milder cases, a complete workup is recommended as soon as possible to pinpoint the cause. Staging diagnostic tests on severe cases is not necessarily a good idea as getting to the diagnosis as quickly as possible will lead to better outcomes. Rabbits also have a high ability to compensate for severe diseases and disease severity may not be appreciated early in case management. If a cause is identified early such as dental disease, other diagnostic tests should still be offered as comorbid diseases are not uncommon. In case of financial limitations from the owner, tests should be prioritized based on a problem-oriented approach. In general, the following tests are recommended (in addition to the initial database including a blood gas/electrolyte panel):

• CBC, biochemistry: To screen for general health, azotemia, and increased liver values (liver lobe torsion, hepatic lipidosis).
• Fecal floatation: mainly for young rabbits, in which intestinal and hepatic coccidiosis are common.
• Urinalysis
• Imaging: whole-body CT scan is best to assess otitis, dental disease, dental abscesses, rhinitis, liver lobe torsion, hepatic lipidosis, gastric volvulus, gastric obstruction, cecal impaction, uterine adenocarcinoma in females, and thymoma or whole-body radiographs (but less sensitive for most of these diseases). Abdominal ultrasound has also a high sensitivity for liver lobe torsion, small intestinal obstruction, abdominal masses, cystitis, and other conditions. It should be noted that small animal ultrasonographers frequently misdiagnose gastric obstruction based on motility disorder, gastric dilation, and presence of gastric content. However, small intestinal obstructions are readily diagnosed and ultrasound can also be useful to rule out a gastric outflow obstruction when the pylorus is clearly seen as patent.
• Stomatoscopy: as part of the dental disease workup.
• Sign- and lesion-specific tests such as deep nasal swab for rhinitis, ophthalmologic assessment, skin biopsies, fine-needle aspirate of masses, E. cuniculi diagnosis, urinary culture and so on.

Step 3: Treatment

Generalities

As mentioned above, most gastrointestinal cases are medical cases. Gastrointestinal obstruction should not be misdiagnosed on the sole basis of an enlarged stomach on imaging, abdominal palpation, and the degree of pain. While hyperglycemia has been implicated as a marker of gastrointestinal obstruction in rabbits, it should only be considered as a risk factor as it also occurs with hypovolemic rabbits, stressed rabbits, and overall increased sympathetic tone. In gastric obstruction, there is generally a strong hypochloremic metabolic alkalosis, the stomach tends to be even larger than medical cases (but some medical cases can have a large stomach too), fluid filled, and some rabbits show regurgitation efforts. Gastric dilation and volvulus is also a possibility, but is rare. Some obstructed cases seem to unobstruct spontaneously or unobstruct with aggressive medical therapy. Therefore, if the owner is unwilling to proceed with surgery, it is still worth pursuing 24 h of aggressive supportive care. Finally, common non-intestinal surgical cases include liver lobe torsion and urolithiasis.

In addition to addressing the causes, the treatment is generally aimed at reversing homeostatic abnormalities (hypothermia, electrolytes, acid-base disorders, glycemia, dehydration, hypotension, and so on), addressing pain (both GI pain and extra-GI pain), preventing existent or potential complications (dysbiosis, sepsis, bacterial translocation, further dehydration, negative energy balance leading to hepatic lipidosis), promoting gastrointestinal motility in non-obstructive cases, and limiting recurrences. All problems should be addressed, even if not primary (such as corneal ulcers, external otitis, perineal dermatitis), as they may contribute to overall pain leading to anorexia. Rabbits may take up to 5 days to start defecating again in cases of prolonged anorexia.

In any case, the following procedures or treatments are not adequate: performance of maintenance fluid therapy in unstable patients (generally SC), performance of enemas, administration of IV dextrose without knowing the glycemia (as most rabbits are normo- or hyperglycemic when in gastric stasis), going to surgery on a non-obstructed case (not uncommon).

Mild Gastric Stasis

Mild gastric stasis is characterized by subclinical dehydration in an otherwise bright and alert rabbit that is also normothermic, normotensive, with no to mild acidemia and the absence of poor prognostic indicators (see previously). In these cases, subcutaneous fluid replacement therapy is sufficient. The fluid requirement of rabbits is high at about 100 ml/kg/day. However, many rabbits become polyuric when rehydrated at this fluid dose indicating that it may be too much in some rabbits. Drugs that are frequently given include ranitidine or maropitant⁶ as a mild motility enhancer and gastric protectant at 1 mg/kg, a SC opioid (either buprenorphine or hydromorphone), meloxicam at 0.5 mg/kg PO q 12 h, and metronidazole at 20 mg/kg PO q 12 h (for possible anaerobic dysbiosis). Likewise, no scientific data are available for the clinical use of trimebutine in rabbits. Assisted feeding with a critical care formula for herbivores should also be performed at 50 ml/kg/day divided into 3–4 feedings. If possible, physical exercise in a run once to twice daily stimulates gastrointestinal motility. Most of these cases improve fairly quickly.

Moderate Gastric Stasis

It is characterized by mild-to-moderate clinical dehydration, acidemia, azotemia, depressed attitude, or as a non-improving mild gastric stasis. Treatment should be more aggressive for these cases and the prognosis is generally good but treatment may be long on some cases. Fluid replacement therapy should be given intravenously and acid-base and electrolytic disorders should be corrected. Most of these cases are acidemic, so Plasmalyte-A is the fluid of choice. Fluid requirement should be calculated and an abbreviated formula of several times the maintenance should not be used in rabbits as the maintenance rate is very high (100 ml/kg/day), which will result in fluid overload (with potential pleural effusion). Potassium should be added to the fluids like in dogs and cats.

Intravenous drug constant rate infusion (CRI) should also be instituted. Fentanyl is a more potent analgesic than buprenorphine and can be given at 3–5 μg/kg/h IV. Lidocaine is an effective gastrointestinal promotility drug, is also an analgesic, and has protective effects against toxemia. The dose in rabbits is high at 50–100 μg/kg/h IV.⁷ Lidocaine, to the author’s knowledge, is the best promotility drug in rabbits. Traditionally used GI motility enhancers, such as metoclopramide and cisapride, do not seem to have much benefit in rabbits and the author does not use them. Some rabbits will chew the IV lines and then worsen as a result, which is the main disadvantage of IV CRI therapies in this species. Antibiotic therapy is also recommended with, for instance, a combination of metronidazole/enrofloxacin (depends on causes and other clinical endpoints). Gastric protectants are also indicated as gastric ulcers are not uncommon on necropsy. Ranitidine or famotidine are favored by the author. Syringe feeding should be delayed by 12–24 h after admission as most rabbits are reluctant to swallow at that stage. If liquid diarrhea is present, oral Bio-sponge® can be given to bind potential clostridial toxins. Transfaunation may be indicated with persistent diarrhea. If the rabbit is refractory to syringe feeding, a nasogastric or esophagostomy tube may be considered, but it is seldom indicated in the author’s experience.

Severe Gastric Stasis

Severe cases are characterized by moderate to severe dehydration, moderate to severe pain, large stomach, and the presence of bad prognostic indicators. Generally, the procedures describe in Step 1 should be performed as well as the administration of norepinephrine. Once the rabbit is stabilized, it can be treated as for moderate gastric stasis. The use of lidocaine should just be delayed as it is hypotensive in rabbits.

Conclusion

In conclusion, it should be repeated that most gastric stasis rabbits are medical cases, but surgical cases nevertheless do occur and should be diagnosed as early as possible. Once the patient is stable, a complete diagnostic workup including many tests should be performed to diagnose the inciting cause in order to initiate specific treatments. In general, the treatment should be relatively aggressive in all but the mildest cases with the use of IV treatments, drug CRIs, and reversal of acid-base and electrolytic disorders with fluid additives. In particular, the use of lidocaine is strongly recommended as a GI motility enhancer and analgesic, and norepinephrine as a vasopressor.

References

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