Definition

• Constipation-infrequent, incomplete, or difficult defecation with passage of hard or dry feces.
• Obstipation-intractable constipation caused by prolonged retention of hard, dry feces; defecation is impossible in the obstipated patient.

Pathophysiology

• Constipation can develop with any disease that impairs the passage of feces through the colon. Potential causes include congenital vertebral malformation, spinal cord disease, pelvic canal narrowing (trauma), rectal mass lesions causing obstruction, and perianal disease causing painful defecation. Often in cats, no underlying etiology can be identified.
• Delayed fecal transit allows removal of additional salt and water, producing drier feces. Clinical signs are attributable to dehydration and potential toxemia resulting from fecal retention.
• Peristaltic contractions may increase during constipation, but eventually motility diminishes because of smooth muscle degeneration secondary to chronic overdistension.

Systems Affected

Gastrointestinal

Genetics

N/A

Incidence/Prevalence

Common clinical problem in older cats; less common in dogs.

Geographic Distribution

N/A

Signalment

Signs

Causes

Risk Factors

• Drug therapy-anticholinergics, narcotics, barium sulfate
• Metabolic disease causing dehydration
• Intact male-perineal hernia, prostatic disease
• Perianal fistula
• Pica-foreign material
• Excessive grooming-hair ingestion
• Decreased grooming/inability to groom-longhaired cats, pseudocoprostasis
• Pelvic fracture

Differential Diagnosis

• Dyschezia and tenesmus (e.g., caused by colitis or proctitis)-unlike constipation, associated with increased frequency of attempts to defecate and frequent production of small amounts of liquid feces containing blood and/or mucus; rectal examination reveals diarrhea and lack of hard stool.
• Stranguria (e.g., caused by cystitis/urethritis)-unlike constipation, can be associated with hematuria and abnormal findings on urinalysis (pyuria, crystalluria, bacteruria).

CBC/Biochemistry/Urinalysis

• Usually unremarkable.
• May detect hypokalemia, hypercalcemia.
• High PCV and total protein in dehydrated patients.
• High WBC in patients with severe obstipation secondary to bacterial or endotoxin translocation, abscess, perianal fistula, prostatic disease.
• Pyuria and hematuria with prostatitis.

Other Laboratory Tests

• If patient (dog) is hypercholesterolemic, consider a thyroid panel to rule out hypothyroidism.
• If patient is hypercalcemic, consider parathyroid hormone assay.

Imaging

• Abdominal radiography documents severity of colonic impaction. Other findings may include colonic or rectal foreign body, colonic or rectal mass, prostatic enlargement, fractured pelvis, dislocated hip, or perineal hernias.
• Pneumocolon (after enemas to clean colon) may better define an intraluminal mass or stricture.
• Ultrasonography may help define extraluminal mass and prostatic disease.

Diagnostic Procedures

Colonoscopy may be needed to identify a mass, stricture, or other colonic or rectal lesion; rectal/colonic mucosal biopsy specimens should always be obtained.

Appropriate Health Care

• Remove or ameliorate any underlying cause if possible.
• Discontinue any medications that may cause constipation.
• May need to treat as inpatient if obstipation and/or dehydration present.

Nursing Care

Dehydrated patients should receive IV (preferably) or SC balanced electrolyte solutions (with potassium supplementation if indicated).

Activity

Encourage activity

Diet

Dietary supplementation with a bulk-forming agent (bran, methylcellulose, canned pumpkin, psyllium) is often helpful, though they can sometimes worsen colonic fecal distension; in this case, feed a low-residue-producing diet.

Client Education

Feed appropriate diet and encourage activity.

Surgical Considerations

• Manual removal of feces with the animal under general anesthesia (after rehydration) may be required if enemas and medications are unsuccessful.
• Subtotal colectomy may be required with recurring obstipation that responds poorly to assertive medical therapy.

Drug(s) Of Choice

• Emollient laxatives-docusate sodium or docusate calcium (dogs, 50–100 mg PO q12–24h; cats, 50 mg PO q12–24h).
• Stimulant laxatives-bisacodyl (5 mg/animal PO q8–24h). Ensure that animal is not obstructed prior to use of stimulant laxatives.
• Saline laxatives-isosmotic mixture of polyethylene glycol and poorly absorbed salts; usually administered as a trickle amount via nasoesophageal tube over 6–12 hours.
• Disaccharide laxative-lactulose (1 mL/4.5 kg PO q8–12h to effect).
• Warm water enemas may be needed; a small amount of mild soap or docusate sodium can be added but is usually not needed; sodium phosphate retention enemas (e.g., Fleet; C.B. Fleet Co., Inc.) are contraindicated because of their association with severe hypocalcemia.
• Suppositories can be used as a replacement for enemas; use glycerol, bisocodyl, or docusate sodium products.
• Motility modifiers can be administered-cisapride (dogs, 0.3–0.5 mg/kg PO q8–12h; cats, 2.5–10 mg/cat PO q8–12h may stimulate colonic motility; indicated with early megacolon.

Contraindications

• Lubricants such as mineral oil and white petrolatum are NOT recommended because of the danger of fatal lipid aspiration pneumonia due to their lack of taste.
• Fleet enemas.
• Anticholinergics.
• Diuretics.

Precautions

Cisapride, and cholinergics-can be used with caution; contraindicated in obstructive processes. Avoid the use of metoclopramide because it does not affect the colon.

Possible Interactions

N/A

Alternative Drug(s)

• Ranitidine causes contraction of colonic smooth muscle in vitro.
• Newer generation cisapride-like drugs may be available soon.
• Pilot studies in Europe demonstrate improved ease of defecation following the administration of multistrain probiotic bacteria.

Patient Monitoring

Monitor frequency of defecation and stool consistency at least twice a week initially, then weekly or biweekly in response to dietary and/or drug therapy.

Prevention/Avoidance

Keep pet active and feed appropriate diet.

Subcutaneous fluids to ensure hydration can help reduce the frequency of constipation, particularly in cats.

Possible Complications

• Chronic constipation or recurrent obstipation can lead to acquired megacolon.
• Overuse of laxatives and enemas can cause diarrhea.
• Colonic mucosa can be damaged by improper enema technique, repeated rough mechanical breakdown of feces, or ischemic necrosis secondary to pressure of hard feces.
• Perineal irritation and ulceration can lead to fecal incontinence.

Expected Course and Prognosis

Varies with underlying cause

Associated Conditions

Vomiting-with severe/prolonged obstipation

Age-Related Factors

N/A

Zoonotic Potential

N/A

Pregnancy/Fertility/Breeding

N/A

Synonyms

• Colonic impaction
• Fecal impaction

See Also

Megacolon

Abbreviations

• PCV = packed cell volume
• WBC = white blood cell

Client Education Handout Available Online