Page 455 - Cote clinical veterinary advisor dogs and cats 4th

Constipation/Obstipation and Megacolon 203

Initial Database in the most severely obstipated/impacted cats functional colon and is well hydrated. Avoid
• CBC: unremarkable or leukocytosis (mature to prevent additional injury or rupture of high-fiber diets in patients that are prone
VetBooks.ir • Serum biochemistry profile: unremarkable • Warm water enemas (5-10 mL/kg water) • Low-residue diets are often best used in Diseases and Disorders
the diseased colon.
to dehydration (high-fiber content can
neutrophilia/stress leukogram), occasionally
exacerbate colonic mucosal dehydration).
anemia
using a 12-14 Fr, well-lubricated, red rubber
or azotemia (associated with dehydration
or concurrent chronic kidney disease), catheter are usually well tolerated (p. 1099). patients with chronic recurrent obstipation
Higher volumes of water must be used with
or true megacolon because they reduce the
hypokalemia, hypercalcemia caution because they may cause vomiting amount of material reaching the colon and
• Urinalysis: no specific changes. Isosthenuria (and aspiration). make it easier to maintain a soft stool.
with azotemia if chronic kidney disease • Enemas should not contain soaps or other
• Abdominal radiographs irritants; lactulose or mineral oil can be used. Possible Complications
○ Feces-distended colon. Ratio of maximal • Enemas containing sodium phosphate (e.g., • Medical treatment: perforation secondary to
diameter of colon to length of fifth lumbar Fleet) are contraindicated in cats and small trauma from enemas and evacuation of feces;
vertebra > 1.48 defines megacolon in cats. dogs because they can cause severe hyper- gentle manipulation, and being patient (do
Ratio of maximal diameter of colon to phosphatemia, hypocalcemia, and death. not be in a hurry to remove the concretion)
length of seventh lumbar vertebra > 1.5 • Broad-spectrum antibiotics (e.g., ampicillin are essential.
defines megacolon in dogs. sulbactam 22 mg/kg IV q 6-8h and enro- • Subtotal colectomy: leakage, dehiscence,
○ Underlying cause of initial colonic floxacin 5-10 mg/kg diluted 1 : 1 in saline and peritonitis; chronic diarrhea (may be
distention/fecal retention may be evident and given slowly IV q 24h [dogs] or cefoxitin associated with bacterial overgrowth from loss
(pelvic fractures, evidence of spinal trauma 10-30 mg/kg q 8h [cats]) are indicated if of ileocolic sphincter); recurrent constipation;
[vertebral fracture/luxation], extraluminal signs of endotoxemia or fever are noted. stricture
compressive mass, foreign material in
colon). Chronic Treatment Recommended Monitoring
• Medical therapy includes stool softeners or • For cats undergoing medical management,
Advanced or Confirmatory Testing laxatives (e.g., polyethylene glycol PEG 3350 close observation of fecal passage by the
• Ultrasonography identifies suspected extralu- [Miralax] 1 8 - 1 4 teaspoon [0.6-1.3 mL] owner is essential for prevention of severe
minal masses. Poor utility for intraluminal powder/CAT PO q 12h, or lactulose recurrent constipation.
visualization because even minute amounts 0.25-0.5 mL/kg PO q 8-12h, or docusate • After subtotal colectomy, monitor
of colonic gas block ultrasound waves sodium/dioctyl sulfosuccinate 50 mg/CAT ○ Hydration
• Barium enema defines strictures or intralu- PO q 12-24h) and prokinetics (cisapride ○ Appetite
minal masses. 0.1-1 mg/kg PO q 8-12h or 2.5-5 mg/CAT ○ Temperature, blood glucose, abdominal
• Endoscopy identifies colorectal neoplasia, PO q 8-12h). Polyethylene glycol is easier to pain (signs of leakage or dehiscence of
stricture, inflammatory lesions, sacculations use than lactulose (not sticky). The dosage anastomosis)
and diverticula, and other conditions. for any of these is titrated to produce a soft
• Evaluation of animals with suspected to semiformed stool. PROGNOSIS & OUTCOME
neurologic impairment may include • Bulk-forming laxatives (cellulose, psyllium)
cerebrospinal fluid analysis (pp. 1080 and will not be effective in cats prone to dehydra- • Fair prognosis with medical manage-
1323), CT/MRI scanning of distal spinal tion or in cats with poor colonic muscle ment. Recurrent constipation requiring
cord and cauda equina region (p. 1132), function because their mechanism of action repeated enemas and manual evacuation is
myelogram, and electrophysiologic studies is similar to high-fiber diets. common.
(electromyography). • Stimulant laxatives (e.g., bisacodyl, castor • Good to excellent prognosis in cats with
• Diagnosis of dysautonomia, a rare cause of oil, cascara) should not be used for relieving subtotal colectomy. Owner needs to be
megacolon, is based on finding other systemic constipation but are best used as a preven- aware that stools are usually soft and the
evidence of the disease (megaesophagus, tive in cats that still have normal colonic frequency of defecation is increased for 2 to
mydriasis, decreased lacrimation, prolapsed function. 3 months after surgery. Occasionally, diarrhea
nictitans, and bradycardia). • Prokinetic therapy may assist smooth-muscle is a persistent, long-term problem.
function in cats with recurrent constipation ○ Guarded to fair after subtotal colectomy
TREATMENT or obstipation. The most effective drugs in dogs. Because of species differences in
are the serotonergic agonists (cisapride, rectal blood supply, there is a greater risk
Treatment Overview prucalopride [available in Europe, Canada, of rectocolic anastomosis site dehiscence
Mild to moderate constipation is usually suc- and Israel]). in dogs. Persistent diarrhea/soft stool is
cessfully treated with a combination of enemas, • Correct underlying cause when present: more common in dogs, depending on how
laxatives, colonic prokinetic agents, and diet remove masses or strictures causing obstruc- much colon is resected.
modification. Patients with severe constipation tion to outflow, or correct pelvic fractures • Guarded prognosis with pelvic osteotomy/
often also require intravenous fluid therapy and obstructing outflow with pelvic osteotomy. hemipelvectomy for pelvic fracture malunion;
manual extraction of feces under anesthesia. • Subtotal colectomy (with or without preser- correction of obstruction may not resolve
Subtotal colectomy is necessary for patients vation of the ileocolic valve) may be indicated megacolon and constipation.
with end-stage megacolon. See p. 1407 for a if lack of response to medical treatment or
recommended treatment approach and protocol. pelvic fracture malunion > 6 months from PEARLS & CONSIDERATIONS
onset of obstipation.
Acute General Treatment Comments
• Fluid therapy for dehydration to assist in Nutrition/Diet • Correction of pelvic malunion by pelvic
constipation relief through rehydration of • Control recurrent constipation with high- osteotomy/hemipelvectomy if > 6 months
the colonic mucosa fiber/low-residue diet; prescription diets from onset of signs of obstipation will most
• Enemas and careful manual extraction of specifically designed to meet this need are likely result in recurrence of obstipation and
feces if obstipated. In most cats, sedation available. the need for subtotal colectomy.
or anesthesia will be required. Multiple • High-fiber diets induce colonic contraction • Do not perform enema immediately before
procedures over a day or two may be needed and are useful when the patient still has a surgery for megacolon. It is more difficult

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