Fecal Impaction

Pathophisiology and Management of Fecal Impaction

Fecal impaction is a condition in which stool blocks the intestinal lumen and can cause significant obstruction in the normal gastrointestinal process in which digested food passes from the stomach to the intestines and then into the colon and rectum

Medications such as narcotics predispose to this problem. It is also a common complication of anorectal procedures as a result of reflex spasm of the anal sphincter. Painful anal fissures Opens in new window may cause the same problem.

Physically and mentally incapacitated persons and institutionalized older adults are at greater risks. Patients with neurologic disorders affecting the nerves that innervate the muscles of the intestines are also at risk. Many of these patients receive regular laxatives and stool softeners, which alters their elimination patterns and contributes to impactions and ultimately fecal incontinence Opens in new window (McKay et al., 2012).

The risk factors include a history of constipation with decreased colonic motility, poor eating habits, severe rectocele leading to trapping of stool in the rectal vault, and patient immobility.

The pathophysiology involves a combination of these factors, which result in stasis of stool and reabsorption of water, leading to hardening of the stool. This is aggravated by continuous colonic motility, which packs the stool in the rectum. Because of the decreased sensation, the rectoanal reflex becomes dysfunctional, leading to an inability to coordinate defecation. The result is a large bolus of hard stool in the rectal vault, leading to obstruction.

The patients are generally elderly and often present acutely with symptoms of constipation Opens in new window including nausea, vomiting, severe abdominal pain, rectal discomfort, diarrhea (leaking around the impacted stool), anorexia, urinary frequency and fecal incontinence Opens in new window. Varieties of interventions (e.g., diet and exercise) normally successfully relieve constipation and reduce the risk of impaction.

With severe posterior compartment distension, the urinary tract Opens in new window may also be affected and patients may present with chronic urinary tract infections or irritative voiding.

Diagnosis

Fecal impaction should be suspected when a patient has unexplained constipation or diarrhea. Diarrhea occurs as liquid stool passes around the hard fecal bolus. Rectal distention from the fecaloma causes reflex relaxation of the internal anal sphincter.

The patient may have acute or chronic large bowel obstruction Opens in new window, both clinically and by radiographic examination. The chronic obstruction will increase mucosal water and electrolyte secretion, leading to frequent, loose, watery stools that pass around the bolus. The patient with spinal cord injury may demonstrate autonomic hyper-reflexia with pain, fever, tachycardia, and abdominal distention.

The patient’s history including bowel habits, systemic disease (i.e., diabetes, multiple sclerosis, hypercalcemia, hypothyroidism), dyschezia, or a history of fecal evacuation disorders should be obtained. The need for the patient to use perineal splinting, digital disimpaction, or unusual positions during defecation suggests pelvic outlet dysfunction. If a sensation of rectal fullness predominates, this could indicate rectal prolapse Opens in new window, internal intussusceptions, or rectocele.

Digital rectal examination reveals impacted feces palpated in the rectum. It is important to assess for size and consistency of the bolus as well as for the presence of blood. In the normal situation, the rectal ampulla remains empty. A fecal bolus does not pass beyond the rectosigmoid junction until the act of defecation commences.

Physical examination may reveal a distended abdomen and large hard stool in the vault. Occasionally, impaction may be proximal to the reach of a digital examination. If diagnosis is apparent on history and physical examination, and there is no suspicion of an acute intra-abdominal process, and electrolyte abnormalities have been ruled out, these patients can be treated in the emergency room (ER). Otherwise, a more extensive workup including radiographic evaluation is warranted.

Complications of fecal impaction can include acute or chronic bowel obstruction Opens in new window, mucosal ulceration, and hemorrhage Opens in new window. Fecal impaction can potentially result in bowel obstruction, causing aspiration, stercoral ulcers (loss of bowel integrity from the pressure effects of dried, thickened feces), and perforation.

After disimpaction, particularly in the recurrent setting, it is important to rule out an anatomic cause of obstruction. This may require proctosigmoidoscopy or a water-soluble contrast examination. Impaction may be associated with an anal or rectal stricture. The practitioner must assess for the presence of a tumor. Last, a deep mucosal ulcer may cause bleeding or infection as a result of fecal impaction, a condition known as stercoral ulceration.

Medical Therapy and Treatment

An attempt at medical therapy in an otherwise ambulatory patient is a reasonable first step. Careful administration of one or two Fleet enemas into the bolus to soften and hydrate the stool should be followed in 1 hour by the administration of a mineral oil enema to assist in passage of the softened stool.

Soapsuds, hot water, or hydrogen peroxide enemas are discouraged because they may irritate the mucosa and result in bleeding. An alternative is an attempt at antegrade cleansing with either mineral oil or polyethylene glycol (PEG) solution lavage. The dose of mineral oil is 30 mL/10 kg orally in two divided doses for 2 consecutive days. The dose of PEG solution is 20 mL/kg daily for 2 consecutive days.

Manual disimpaction is required in most patients. This is best performed after a circumanal block of the anal musculature with local anesthetic. A four-quadrant field block allows for complete muscle relaxation and a painless disimpaction. Use 0.5% lidocaine drawn up in a 10-mL syringe. A 22-gauge, 1¹/₂-inch needle is used. Insert the needle all the way to the hub in each of the right, left, anterior, and posterior positions 1 cm away from the anal verge. “Fan it out” in three directions at each of the injection sites, depositing a total of 2 to 3 mL of local anesthetic in each of the four sites as the needle is slowly withdrawn. The left decubitus position with hips and knees flexed to the chest is the most comfortable for the patient.

Gentle digital dilation of the sphincter is then performed as the fecal bolus is fragemented and extracted. A large, rigid proctoscope may be necessary to soften and break up stool residing higher in the rectum. After passing the rigid scope up to the fecal bolus, phosphate enema solution is passed through the scope to soften the stool. A long rigid aspirator is then passed through the scope to break up the softened stool and allow for evacuation. This process is repeated as many times as necessary to empty the bowel of stool.

Disimpaction may be facilitated by intravenous or intramuscular administration of a narcotic or anxiolytic. Early posthemorrhoidectomy impaction may be managed best in the emergency room (ER) under general or regional anesthesia.

After disimpaction, it is prudent to institute a bowel habit program that includes laxatives, stool softeners, or enemas along with a regular time for evacuation to prevent reimpaction. PEG solution can be useful to treat patients with chronic constipation prone to develop recurrent impaction.