Page 644 - Clinical Small Animal Internal Medicine

612 Section 6 Gastrointestinal Disease

Prognosis as seen with chronically obstructed urinary bladders.
VetBooks.ir Surgical repair of type I or II atresia ani often results in Similarly to the urinary bladder, loss of large bowel
intrinsic motility is almost universally irreversible,
long‐term survival and fecal continence. Patients with
type III or IV atresia ani have poorer outcomes and the resulting in megacolon.
prognosis depends on the possibility of reconstructing
the terminal rectum. Diagnosis and Medical Management
Prognosis following treatment for anorectal stricture
largely depends on the underlying cause. Benign causes A history of unproductive straining or tenusmus, in con-
cert with a readily palpable, heavily feces‐laden large
may carry a good prognosis but strictures associated intestinal loop in the mid to distal abdomen, establishes
with rectal adenocarcinoma are associated with a more a diagnosis of constipation readily. Differentiation of
guarded to poor prognosis. Surgical complications constipation/obstipation from megacolon can be more
following rectal stricture resection and anastomosis challenging, however. On plain abdominal radiographs,
may include dehiscence with sepsis and/or recurrence of measurement of the maximal colon diameter:L5 verte-
stricture.
bral body length ratio has been suggested as a method to
help differentiate constipation from megacolon. A colon
Constipation, Obstipation, and diameter:L5 length ratio of >1.48 has a sensitivity of
Megacolon approximately 77% with a specificity of 85% for estab-
lishing a diagnosis of megacolon. Similarly, a ratio of
Clinical Presentation <1.28 is a strong indicator of a normal colon (sensitivity
96%, specificity 87%).
Constipation and obstipation are both manifestations In patients where imaging findings do not suggest the
of difficult defecation, and fall within a spectrum of presence of megacolon, medical treatment for constipa-
severities. Constipation is defined as difficult or effort- tion and obstipation is indicated. Particularly for patients
ful defecation, but feces is passed after some effort. with obstipation, it is critical to clearly indicate to the
Obstipation is a state of more severe constipation, and animal’s owners that failure to treat effectively may lead
may result in intestinal obstruction. Both constipation to life‐long, severe consequences.
and obstipation are the result of disorders in large Most uncomplicated cases of constipation can be
bowel motility that slow fecal transit, but an implica- treated with warm water, saline or water‐lubricant ene-
tion of both diagnoses is that there is some degree of mas. Laxative medications, such as lactulose or emol-
large bowel and rectal motility remaining. Obstipation lient, paraffin‐based products, can be trialed. The diet
should be treated aggressively, and the early use of pro- history should be considered, and addition of indigesti-
motility agents is recommended in many cases, as fail- ble fiber as a bulking agent may be necessary. In patients
ure to restore functional motility in these patients can with more severe disease, and definitely if constipation
result in progression to megacolon, a state in which all has progressed to obstipation, more aggressive treat-
large bowel and normal rectal motility is lost. Once ment may be required.
established, megacolon is not effectively treated with Some patients with long‐standing constipation/obsti-
laxative or prokinetic medications, as both of these pation can present with quite severe dehydration, elec-
families of medications require some degree of intrinsic trolyte, and acid–base abnormalities; this is particularly
motility in order to be effective. common in feline patients. Patients presenting with evi-
dence of significant dehydration and fluid deficits should
Pathophysiology be stabilized with parenteral fluid therapy, possibly over
24 hours or more, before anesthesia for deobstipation
Constipation and subsequent obstipation can result and enema therapy. In these patients, the dehydration is
from any disorder or abnormality that slows fecal tran- more immediately life threatening than the fecal load,
sit through the large intestine, decreases large intestinal which has typically been present for days to weeks.
and rectal motility, or mechanically obstructs passage Patients with obstipation should be treated with
of the fecal material to the rectum and anus. Slower prokinetic medications after obstipation is relieved.
passage of fecal material results in greater dehydration Unfortunately, only a small number of medications is
of the large intestinal content, as water absorption by available that may assist with large intestinal motility.
the large intestinal mucosa continues unabated. Two medications with at least some evidence to suggest
Progressive overloading of the large intestine will even- they are worth trialing are low‐dose erythromycin and
tually lead to large intestinal atony and flaccid paralysis, cisapride.