Constipation is a common issue seen in small animals, especially cats, and is defined as difficulty with fecal evacuation. Obstipation is a subset of constipation where fecal material is unable to be evacuated, often resulting in a mass of dry, hard feces that accumulates within the colon, and can lead to impaction of retained fecal material from the distal colon to the ileocolic junction. This can further progress to megacolon, characterized by hypomotility and large intestinal dilation with increasing risk for chronic recurrent constipation and obstipation.
There are a variety of causes for constipation and obstipation, with the most common considerations including:
- Chronic kidney disease
- Previous constipation events
- Electrolyte abnormalities (hypercalcemia, hypokalemia)
- Pelvic narrowing or orthopedic disease (trauma, arthritis)
- Intra- or extra-luminal colonic compression (such as masses)
- Caudal neurologic abnormalities (Manx breed cats)
- Medication administration (opiates, sucralfate)
- Dietary intake/indiscretion (high fiber, sand/rock/bone ingestion)
- Idiopathic megacolon
Dogs have similar causes for constipation, but often have less frequent incidents compared to their feline counterparts. Constipation in dogs is most often related to dietary indiscretion with sand, rocks, or bone (raw food diet or chewed bone pieces) as high-risk substances for fecal impaction. If primary causes are readily identifiable, they should be addressed to help correct and reduce the likelihood of recurrent constipation issues.
When first identified, classic signs of constipation include tenesmus, passing small quantities or firm or ribbon like stool, vomiting, vocalization in the litter box, abdominal distention, or anorexia. Fecal accumulation resulting in obstipation can take days to weeks—during that time animals may have a slow onset of appreciable signs with an acute change once complete impaction has occurred.
Initial physical exam will reveal a large, firm tube of feces palpable within the caudal abdomen. Patients may be uncomfortable on abdominal palpation and shows signs of dehydration. Rectal examination should always be performed to further confirm a firm fecal impaction as well as assess pelvic canal size and presence of any mass lesions within the distal colon. Often, a distal, firm fecal plug can be palpated on initial rectal exam and removed that may help alleviate more simple cases of constipation. It is important to also palpate urinary bladder size on intake as signs of constipation can be confused for an actual urethral obstruction by owners. Alternatively, animals can have a secondary functional urethral obstruction from fecal impaction due to colonic compression on the pelvic urethra.
A minimum database is recommended at initial evaluation to determine any predisposing causes of constipation as well as survey radiographs to assess distention of the colon and density of the fecal material. Radiographic findings alone cannot differentiate constipation, obstipation, and megacolon.
Bony impaction in a cat leading to obstipation and functional urethral obstruction.
Obstipation in an overweight cat can result in difficulty of palpation and fecal manipulation during any manual deobstipation procedure.
Treatment options are variable, based on degree of impaction, clinical signs associated, and recurrence of disease. Initial treatment goals include correction of dehydration and electrolyte derangements. Enemas, laxatives, and prokinetics are easy first-line oral therapy options to help encourage passage of impacted stool. If these show limited effect, then more aggressive management can be considered in the form of manual deobstipation or polyethylene glycol 3350 (PEG3350) treatment. In severe, recurrent cases of idiopathic megacolon, surgery may be the only adequate way to prevent recurrent fecal retention through a subtotal colectomy, however this should only be considered in refractory cases where medical management and dietary modification have been exhausted. In a recent retrospective (Benjamin et al, 2020), adjunctive treatments increased the likelihood of success for fecal passage, with older, overweight cats with a history of constipation or CKD more likely to present to the ER for constipation issues.
At-home management can include long-term laxative therapy and dietary modifications. Multiple highly digestible diets exist that are targeted for a moderate fiber to enhance fecal bulk and provide psyllium, including Science Diet® GI Biome and Royal Canin® GI Fiber Response. If diet cannot be changed, psyllium powder can be mixed into the diet directly to encourage fecal passage. Water intake should be encouraged to maintain adequate hydration, as well as weight loss as indicated.
A variety of complications exist with constipation and treatment. Although rare, life-threatening colonic perforation can occur. This is usually only seen with bony or sharp types of impaction or chronicity that can lead to the loss of colon integrity. Prolonged obstipation can result in nerve dysfunction, enhancing the likelihood of recurrence and megacolon. Colonic mucosa can be torn depending on fecal size and pressure required for removal, and electrolyte derangements can result based on treatment modality selected.
Manual deobstipation is a procedure where a combination of serial infusions of lube and water into the colon with alternating digital manipulation of the feces in the rectum and external abdominal massage is used to remove fecal material. The patient is placed under general anesthesia and intubated due to the generally prolonged nature of the procedure and to allow for complete relaxation. Because of the risk of vomiting or regurgitation under anesthesia, premedication with antinausea drugs and close attention to signs of silent regurgitation are important. A large quantity of warm water should be flushed into the rectum with an 8-12fr red rubber catheter. Enema bags exist to help with gravity flow, or a large bowl can be filled with warm water and lubricant and pulled up in 60 mL aliquots with a catheter tip syringe. Using ample lubricant and digital manipulation to break off fecal pieces with the colonic flushing helps keep the stool moving aborally down the intestinal tract. Always attempt to pass the red rubber past the fecal mass to facilitate aboral transit until digital manipulation can occur. Gentle abdominal manipulation can be performed but avoid aggressive palpation that could result in renal avulsion if a kidney is mistaken for a fecal ball. Continue to digitally remove all fecal balls until no more stool is palpable and fluid is flushing clear. A post procedural radiograph is recommended to confirm adequate removal of stool prior to patient recovery. Due to the potential for colonic wall trauma, it is not recommended to use any form of forceps during this procedure.
The use of GoLytelyTM, or PEG3350, has long been considered a preparatory tool for colonoscopy but can also be a tool to manage obstipation. This can be prioritized in patients where general anesthesia is contraindicated or high risk and simple enema therapy has not provided adequate fecal passage. A nasogastric or nasoesophageal tube should be placed with confirmation of appropriate placement location through radiograph prior to instilling the solution. The recommended dose of solution is 6-10 mL/kg/hr through the NG tube until adequate fecal passage occurs—most often seen within 24 hours of treatment induction. It is generally well tolerated with a high success rate and minimal complications, but monitoring for hyponatremia is recommended. Management with anti-emetics is also recommended due to risk of emesis with this disease as aspiration of PEG3350 can result in severe clinical compromise. It is also recommended this solution is mixed with food dye to prevent iatrogenic intravenous administration.
Example of an enema bag that can be used with a red rubber at the end to provide colonic flushing.
Once your patient is adequately evacuated, at-home oral laxative management can ensue. A common over the counter oral preparation of PEG3350 (brand name MiraLAXTM) can be given to cats in small amounts mixed in the food without any aversion. Cisapride is a pro-kinetic motility agent that is only available through compounding pharmacies due to discontinuation in human medicine for its arrhythmogenic properties. Lactulose is classically reached for as a laxative, but quantity and consistency can lead to poor patient tolerance and client compliance with long-term use. Oral laxatives are recommended to be titrated to effect with risk of diarrhea from their use. Treatment length is patient specific. First timers may not require prolonged therapy, but if a patient has a predisposing condition and an event of obstipation, careful monitoring and long-term diet and laxative management is recommended to prevent recurrence and avoid the risk of megacolon.
Benjamin S, Drobatz K. Retrospective evaluation of risk factors and treatment outcome predictors in cats presenting to the emergency room for constipation. JFMS 2020;22.2: 153-160.
Defarges, Alice. Constipation and Obstipation in Small Animals. Merck Veterinary Manual, 2020.
Little, S. The power of Microbiome: feline constipation. Hills Global symposium 2019 Conference proceedings, 17-18.
Byers C et al. Feline Idiopathic megacolon. Compendium, Sept 2006; 658-665.
Carr et al. Constipation resolution with administration of Polyethylene-Glycol solution in cats. ACVIM 2010 Conference proceedings.
Plumb’s Veterinary Drug Handbook. Ed DC Plumb. 9th edition, 2018.