Impaction

Outline

Definition
Pathophysiology
Systems Affected
Signalment
Signs
Causes

BASICS

Definition

An impaction is the obstruction of the GI tract, and depending on the portion affected may result in a variety of clinical signs. The obstruction may consist of feed material, fecal material, or foreign matter that slows or stops the movement of ingesta. This may result in distention of a viscus, causing abdominal pain. Impactions may be primary or secondary, and may cause partial to complete obstructions.

Pathophysiology

Any disease that causes decreased gastric or intestinal motility may cause an impaction. There are feed-associated factors (coarse, high-fiber, low-digestible feedstuffs), and insufficient water intake, poor dentition, or a change in diet that may affect the breakdown of feed material resulting in delayed passage. Factors such as dehydration, change in exercise, and transport are thought to be important in initiating an obstruction. In addition, general anesthesia and surgical manipulations may affect the GI motility; therefore, postanesthetic impactions are not uncommon. Portions of the bowel where the intestinal lumen size narrows are common areas for impactions. These include the stomach, distal small intestine, cecum, pelvic flexure, right dorsal colon, transverse colon, and small colon. Impactions may also occur in areas where pacemakers controlling motility are located (cecum, pelvic flexure). In some cases, the cause of impactions may not be delineated.

Systems Affected

Decreased appetite
Decreased fecal output
Increased or decreased borborygmi
Abdominal distention
Colic
Diarrhea
Other signs caused by primary disease

Behavioral

Vague changes in demeanor to severe signs of colic and toxemia.

Cardiovascular

Normal to increased heart rate and capillary refill time
Tacky mucous membranes
Cardiovascular compromise as severity increases

Renal/Urologic

Changes associated with hypovolemia.

Respiratory

Mild tachypnea
Shallow respiration due to pain and abdominal distention

Skin/Exocrine

Sweating

Signalment

Any age, breed, or sex
Ascarid impactions—occurs in foals, weanlings, and yearlings
Small colon impactions—may be more common in ponies and American Miniature Horses
Cecal impaction—more common in postparturient mares and in horses following general anesthesia for nonabdominal surgeries

Signs

Abdominal distention
Anorexia (partial to complete)
Decreased fecal output
Diarrhea—sand impaction, small colon impaction, although may occur in course of treatment of other impactions
Feces—firm/hard, dry, mucus covered
Flank watching
Frequent attempts to defecate
Increased or decreased borborygmi
Lethargy
Nasogastric reflux
Pawing
Rectal prolapse
Recumbency
Rolling
Straining to defecate
Tail swishing

Causes

Gastric Impaction

Abrupt increase in amount of food, especially those that swell; outflow obstructions due to pyloric dysfunction or gastric mass, or small intestinal ileus or other disease that decreases small intestinal motility.

Small Intestine Impaction

Associated with coastal Bermuda grass, with mesenteric vascular disease, or with ileal wall thickening; ascarid impactions in young horses with heavy worm burdens are usually associated with anthelmintic treatments that cause sudden death or sudden paralysis of the parasites (organophosphates, piperazine, pyrantel pamoate), or cause hyperexcitability of the parasite prior to death (ivermectin, moxidectin).

Cecal Impaction

Multifactorial problem that occurs in the adult horse and is rare in foals. May occur as a primary problem due to an abrupt change in feed or may be secondary to altered motility due to general anesthesia, surgery, parturition, or sand ingestion. Parasitic or vascular damage affecting the cecal pacemaker may alter cecal motility.

Large Colon Impaction

Decreased water intake
Diet alteration
Poor dentition
Decreased exercise
Sand ingestion
Enteric parasitism

Small Colon Impaction

Similar to causes of large colon impaction.

Diagnosis ⬆ ⬇

Outline

Differential Diagnosis
CBC/Biochemistry/Urinalysis
Imaging

DIAGNOSIS

Differential Diagnosis

Determination of the cause of colic should include a thorough collection of historical information, physical examination, abdominal palpation per rectum, and passage of a nasogastric tube.

Gastric Impaction

Rule out many other causes of colic, including causes of small intestinal/gastric reflux.

Small Intestine Impaction

Ileal hypertrophy, ileum-associated mass, small intestinal or ileal–cecal intussusception. Other causes of small intestinal distention include proximal duodenitis/jejunitis, small intestinal volvulus, entrapment, and strangulating lipoma.

Cecal Impaction

Differentials for cecal distention include cecocecal intussusception and cecocolic intussusception. For a “simple” cecal impaction, a cecum that is distended with ingesta should be palpable in the upper right abdominal quadrant. A medial and ventral band may be palpated. An apical impaction, early in the disease process, may not be palpable.

Large Colon Impaction

Colon displacements, early large colon/cecal torsions. Impaction of the left large colon should be palpable per rectum. The impacted pelvic flexure is usually located within the pelvic inlet and is positioned with the dorsal and ventral colon in a horizontal plane. A nephrosplenic entrapment may closely resemble a simple impaction of the left colon, but the position of the left colon is often reversed, and the colon and associated bands may be palpated from the pelvic brim to the nephrosplenic space. Ultrasonography is very helpful in making the diagnosis. Palpation of impactions of the right dorsal or transverse colon is not possible, and diagnosis would require a celiotomy or necropsy.

Small Colon Impaction

Major differential is impaction of the small intestine. Differentiation requires the detection of the large anti-mesenteric band on the small colon. Multiple loops of impacted small colon are usually palpable.

CBC/Biochemistry/Urinalysis

Usually normal; abnormalities may occur with progressive disease due to hypovolemia and debilitation of the bowel.

Abdominal Fluid Analysis

The fluid should be normal in appearance and have normal cytologic parameters. Abnormal cell count, cell differential, protein level, presence of bacteria or foreign material consistent with compromised bowel or another problem.

Imaging

Radiographs

Helpful in assessing foal abdomens or searching for foreign bodies, enteroliths, or sand in adult horses.

Ultrasonography

A useful tool in evaluating foal and adult abdomens. Can be used transcutaneously or per rectum to assess intestinal distention (may include loss of sacculations with large colon impaction), intestinal wall thickness, and intestinal motility. Possible to detect intussusceptions and masses, but it has limitations in diagnosis of impaction.

Treatment ⬆ ⬇

TREATMENT

GI Impactions

Resolve primary risk factors
Medical therapy should include withholding feed; however, small amounts of feed may help maintain GI motility and may be considered in impactions of the large or small colon
Further medical therapy may include IV crystalloid fluids given at a high rate to increase the fluid content in the bowel to break down impaction. If tolerated, fluids may be given via an indwelling nasogastric tube at rates up to 6 L/h in a 450 kg horse
Medications may be given orally to soften the feces and analgesics may be administered as needed
Exploratory surgery may be required depending on the type of disease and its severity, duration, and progression

Gastric Impactions

Medical therapy should include withholding feed and maintenance of the hydration status. The stomach may be lavaged through a nasogastric tube; however, caution must be used to prevent further gastric distention and rupture.

Surgical Considerations

Consider abdominal surgery for unmanageable pain, displacement of intestine, abnormal peritoneal fluid, or deterioration in condition.

Medications ⬆ ⬇

Outline

Drug(s) of Choice
Contraindications

MEDICATIONS

Drug(s) of Choice

Laxatives

Mineral oil—2–4 L/450 kg horse, every 12 h via nasogastric tube
DSS—120–240 mL/450 kg horse of 4% DSS with water
Psyllium hydrophilic mucilloid—0.25–0.5 kg/450 kg horse

Cathartics

Magnesium sulfate (Epsom salts)—0.5–1.0 kg every 24 h
Sodium sulfate (Glauber's salts)—0.25–0.5 kg every 24 h

Analgesia and Anti-inflammatory Drugs (NSAIDs)

Flunixin meglumine—0.5–1.1 mg/kg IV every 24 h/12 h/8 h
Ketoprofen—2.2 mg/kg IV every 24 h/12 h/8 h
Phenylbutazone—2.2–4.4 mg/kg IV every 24 h/12 h

Analgesia and Sedation

Xylazine—use α₂-adrenergic agonists sparingly due to decreased motility
Romifidine—40–80 μg/kg IM, IV
Detomidine—10–30 μg/kg IM, IV
Butorphanol—0.01–0.05 mg/kg (some horses may need prior or concurrent α₂-adrenergic agonist)
N-butylscopolammonium (spasmolytic)—0.3 mg/kg IV

Contraindications

NSAIDs

NSAIDs may cause renal papillary and tubular necrosis or GI ulceration; side effects may be worse in a dehydrated animal.

α₂-Adrenergic Agonists

Side effects include transient hypertension followed by longer lasting hypotension, bradycardia, secondary atrioventricular blockade, decreased GI motility, sweating, and diuresis.

Salt Cathartics

Animal must be well hydrated; may cause distention and more severe colic. Toxic to enterocytes with repeated administration.

Follow-up ⬆ ⬇

Outline

Possible Complications
Expected Course and Prognosis

FOLLOW-UP

Possible Complications

Magnesium sulfate therapy can lead to hypermagnesemia, especially if there is deficiency in renal function, hypocalcemia, or compromised vascular integrity.

Expected Course and Prognosis