Small-colon impaction — Some cases can be difficult to diagnose, especially when coupled with diarrhea

Impaction of the small colon has been recognized in horses for many years, but recently it has become apparent that a form of this disease differs from simple fecal impaction of the colon.

Extensive small-colon impactions are best treated by performing a small-colon enterotomy followed by extensive lavage of the entire length of the small colon.

Specifically, horses may develop small-colon impaction during or following an episode of diarrheal disease. This can be very confusing for veterinarians evaluating these cases because horses with active diarrhea typically are not suspected of having impactions.

The pathophysiology is thought to relate to inflammation of the small colon wall, most likely induced by an infectious organism with edematous mucosa reducing the size of the lumen, the result of which is impaction.

Recently at North Carolina State University (NCSU), we have noticed that specific farms have outbreaks of small-colon impaction. Horses will present with signs of infectious diarrhea, including fever, low white blood cell counts and watery feces. These cases are the subject of an ongoing epidemiological study at NCSU by Drs. Lisa Federico and Anthony Blikslager.

Suggested reading

Additional signs, including colic and distended small colon on rectal examination, are suggestive of small-colon impaction. In most instances, the small colon impaction itself can be detected, although it can be difficult to identify when it is markedly distended. Unique organisms that might be associated with small colon impaction have been investigated at NCSU, including viruses, but none have been identified to date.

Culturing for Salmonella, as with any diarrheal case, is indicated, and it certainly is possible that Salmonella could induce small-colon inflammation and impaction.

One particularly confusing finding in some horses with small-colon impaction is the concurrent presence of diarrhea. In these cases, it is thought that colonic fluid is able to move around the impaction, and it is not absorbed by the small colon because of inflammation. Therefore, a horse with diarrhea that becomes painful, particularly if there is development of abdominal distension, should have a rectal examination to assess the possibility of a small colon impaction.

Medical management

Small-colon impaction may be treated medically, including administration of fluids, flunixin meglumine, broad-spectrum antibiotics for horses that appear to be endotoxemic and administration of mineral oil by nasogastric tube. Balanced electrolyte solutions (made up of table salt and lite salt) also can be administered by stomach tube, which has been shown to soften fecal material more efficiently in recent studies compared to intravenous fluids (see Suggested Reading).

Additional treatment for pain can include xylazine and butorphanol (150-200mg and 5-10mg, respectively, for a 1,000-pound adult horse). However, veterinarians should be cautious about treating pain aggressively because more than 50 percent of these cases ultimately will require surgery, and excessive treatment of pain might delay referral or surgery.

Indications for surgery include refractory pain, lack of response to medical therapy and progressive distension of small and large colon.

When palpating horses with this condition, it can be difficult to determine which segment of the colon is impacted or distended. There are occasions where the impaction is within reach inside the rectum, although veterinarians should be very cautious about attempts to remove the impaction with enemas because the small colon likely is inflamed and can rupture.

As the disease progresses, the small colon will become distended, and may feel like large colon. However, the diameter is not as large as the large colon, and loops of distended small colon can be felt within the caudal abdomen, including the pelvic inlet.

The large colon also can be distended as fecal material and gas backs up into the colon. Abdominocentesis can be helpful in determining if there is inflamed small colon that requires surgical intervention. In horses with acutely inflamed and impacted small colon, abdominal fluid often is serosanguineous in appearance with an elevated total protein. More severe cases also will have an elevated white blood cell count.

Surgical intervention

Most surgeons are very aggressive about taking horses with small-colon impaction to surgery because once the small colon becomes grossly distended, motility ceases, and the chances of resolving the impaction medically are low. This is compounded by the fact that the small colon is typically very inflamed as a result of the inciting cause, and it can become irreversibly injured if not managed surgically. At surgery, small-colon enema directed by the surgeon within the abdomen, or small-colon enterotomy is indicated. The enema approach typically is restricted to those cases that have a relatively short segment of small colon impacted close to the anus.

For extensive impactions, surgeon-directed enemas can be very time-consuming and damaging to the small colon because of extensive manipulation. Therefore, extensive small-colon impactions are best treated by performing a small-colon enterotomy followed by extensive lavage of the entire length of the small colon. In addition, it is a good idea to evacuate the large colon at surgery to reduce fecal material entering the small colon during the postoperative recovery period. Additional surgical therapy also should include products that reduce adhesions, given extensive inflammation of the small colon in most of these cases.

For diffuse inflammation, the best treatment is instillation of 250-500ml carboxymethylcellulose solution into the abdomen following abdominal lavage. For specific regions of severe small colon injury and the enterotomy, a commercially available carboxymethylcellulose-hyaluronan membrane can be placed on the site following completion of all other surgical procedures.

Postoperatively, horses should be treated with broad-spectrum intravenous antibiotics, flunixin meglumine and fluids. Horses should be fed very conservatively to avoid repeat impaction. For example, horses may be held off feed for 48 hours, then started on a low-residue feed, such as small quantities of a complete pelleted ration or small periods of grazing if available.

The inflammation in the small colon likely takes three to five days to subside, and re-impaction is a risk during this period. In addition, we have had some repeat cases of small-colon impaction in horses following discharge from the hospital at NCSU, indicating that continued careful feeding of these patients is warranted during the first postoperative month. Complications include diarrhea, peritonitis, endotoxemic shock and adhesion formation (which typically will present as recurrent colic, starting as early as three to five days following the surgical procedure). Because of the possibility of an infectious cause of diarrhea and small colon impaction, practical measures to reduce exposure of effected horses with normal horses on the farm should be taken, including isolating effected horses in a separate barn and handling these horses after all of the other horses during daily care.

The prognosis for horses with small-colon impaction with appropriate medical and surgical attention is fair. Approximately 75 percent of these cases are discharged.

Dr. Anthony Blikslager is associate professor of equine surgery at North Carolina State University. He has a doctorate in gastrointestinal physiology and is board certified by the American College of Veterinary Surgeons. He is an active clinician focused on surgery and critical care of the equine colic patient, and investigates mechanisms of intestinal mucosal injury and repair in a federally funded research laboratory. Dr. Blikslager has written for more than 50 veterinary publications and has authored/edited several textbook chapters on colic and gastroenterology, such as "Current Therapy in Equine Medicine", "Equine Internal Medicine", "Large Animal Internal Medicine" and "Equine Surgery".