Rectal Tears in the Horse
Dr. Melissa Mazan
The veterinarian will usually sedate the horse heavily in order to allow another rectal examination without any straining by the horse.
Emergency Care and Diagnosis In-depth
In the majority of cases, when the rectal tear occurs as a result of a rectal examination, the veterinarian knows right away that the tear has occurred since there will usually be blood on the rectal examination sleeve. Any time a veterinarian sees blood on his sleeve after a rectal examination, he should immediately suspect the worst – a Grade III or IV rectal tear. It is of vital importance to determine right away where and how deep the tear is.
Often, the veterinarian will also infuse the horse's rectum with lidocaine or some other local anesthetic. This will numb the area, and help to prevent the horse from straining.
In some cases, the veterinarian will choose to give the horse an epidural. The epidural is given in the epidural space that surrounds the nerves at the end of the spinal cord. This not only numbs the rectum, but also paralyzes it temporarily. This is the most effective way to prevent the horse from straining.
The veterinarian will then remove her sleeve, and use her bare hand to investigate the tear. This is because the bare hand is much more sensitive than even a very thin glove, and is better suited for determining the location and grade of tear.
If your veterinarian has a long endoscope, she may choose to do a proctoscopy to visualize the tear.
If the tear is a Grade I or Grade II, then your veterinarian will most likely choose to manage the tear on the farm. A mucosal (Grade I) tear usually heals on its own with very minimal management. The veterinarian usually chooses to give broad spectrum antibiotics for 5 to 7 days, administers a tetanus booster, and gives mineral oil using a nasogastric tube in order to produce soft manure. Your veterinarian checks your horse's progress every few days until the tear is healed.
If the tear is a Grade III or Grade IV, then your veterinarian further prepares the horse for referral to a surgical facility. He administers intravenous or intramuscular broad spectrum antibiotics and gives the horse a tetanus booster.
If the veterinarian has not yet performed an epidural, then he should do so now. Your veterinarian will evacuate the horse's rectum thoroughly, and then may pack the rectum to prevent further contamination from occurring. It is very important to have an effective epidural working before this step, otherwise it will worsen the tear.
If your horse has a long ride to the surgical facility, your veterinarian will often choose to give intravenous fluids prior to the ride.
In the case of a grade III or IV tear, your veterinarian will avoid giving mineral oil, as it will be impossible to repair the situation if the mineral oil contaminates the peritoneal cavity.
Although rectal tears caused by a rectal examination are usually immediately apparent, there are occasions when they may go undetected initially.
The veterinarian may suspect a rectal tear if a horse shows signs of colic or shock within hours after a rectal examination. The signs of shock include: high heart rate, pale or brick red mucous membranes, shakiness, collapse, high respiratory rest, increased respiratory effort and cold extremities. The horse may sweat profusely.
At the surgical facility, other diagnostics may include:
A complete blood count. The complete blood count (CBC) helps the veterinarian to determine how severe the infection and inflammation is. In the case of gross contamination of the peritoneal cavity, the white cell count will often be markedly low (leukopenia).
A chemistry profile lets your veterinarian determine if there are problems with the kidney secondary to dehydration and shock.
The blood gas allows the veterinarian to determine if the horse's blood is too acidic – usually due to the production of lactic acid. When a horse is in shock, there is poor perfusion to much of the body – meaning that the blood doesn't get to all the areas that need it. The body starts to use anaerobic metabolism (meaning without oxygen), and produces lactic acid. Overly acidic blood can make an individual very sick.
The abdominocentesis allows the veterinarian to sample the fluid that surrounds the intestines. If there is a grade IV tear, then the peritoneal fluid then there will be plant material, bacteria, and protozoa in the peritoneal fluid. If there is a grade III tear, there will be high numbers of cells and protein in the peritoneal fluid, but there should not be any plant fibers. With a grade I or II tear, there should not be important changes in the peritoneal fluid.
Immediate repair. If the tear is close enough to the anus, then there is the possibility of repairing the tear while the horse is standing. Special instrumentation allows the surgeon to access the tear directly, and do a full repair. Unfortunately, the tear is frequently too far from the anus, and cannot be repaired directly.
Colostomy. The most common surgical technique involves a colostomy and subsequent revision of the colostomy. Both require general anesthesia and a reasonably long surgery. In most facilities each surgery will cost the equivalent of a colic surgery – thus the financial investment is considerable.
With a colostomy, the small colon is transected ahead of the rectal tear. It is then attached to the flank of the horse, so that the horse temporarily defecates through its side. The rectal tear is allowed to heal on its own within the abdomen.
During the surgery to revise the colostomy, the small intestine and rectum are reconnected.
In the time between the two surgeries and for some time after the surgical revision, the manure must be kept moist so that the horse does not strain against it. The opening through the flank with a colostomy is also often smaller than the normal opening, and does not have the same flexibility, so it is more difficult than normal for the horse to defecate.
Complications of Surgery
Even with prompt surgical treatment, peritonitis may be too severe, and the horse may die of shock and sepsis ( this refers to the byproducts of bacterial infection within the bloodstream).
As with any surgery, the horse may have difficulty in recovery, or may have difficulties secondary to anesthesia and the problems inherent in anesthetizing such a large animal.
There is always a possibility that the incision may dehisce, or come apart. This can, obviously, be catastrophic.
The anastomosis, or place where the intestine is joined to the skin for the colostomy, or two pieces of intestine are rejoined, as when the colostomy is revised, may either dehisce or become strictured. In the latter situation, the horse develops a severe impaction where the manure was not able to pass through the intestinal tract.