Also known as cecal tap or trocarization, abdominal decompression involves needle deflation of the colon or cecum, which is the upstream blind sac portion of the large colon.

The equine intestine is 100 feet long and very complex. The large colon, the unique fermentation vat that breaks down roughage into energy, is approximately 80 feet downstream from the mouth. Many conditions causing colic (CCC’s) involve tight gas inflation of this section of intestine. The large colon is a double horseshoe shape; larger than a truck tire in an average size horse.

Gas distention of the colon causes pain, and pain stops normal intestinal movement, preventing transport of gas downstream.

The gas is far from an exit, either upstream or downstream, so in some cases, vet's puncture the horse’s flank (usually through the skin of the right flank) in order to remove gas, thereby taking the stretch off the colon wall, which gives the colon a chance to regain function.

HOW IT'S DONE

An experienced examiner can determine, using a stethoscope (auscultation) whether there is a large accumulation of gas in the region. In a horse that has a gas accumulation here, a high pitched “ping” can be heard through the stethoscope when the horse’s side is flicked with a finger on the skin of the flank. This ping suggests that there is a sufficiently large gas accumulation to warrant the small risk that accompanies this procedure.

The site of the most obvious ping is selected, usually high on the right flank. The hair is clipped, and the skin is surgically prepared. A local anesthetic is injected to numb the skin. The surgeon usually puts on sterile gloves at this time. The skin is punctured with a narrow, sharp, sterile scalpel blade. Then a large, long sterile needle penetrates through the colon (cecum) wall. In cases in which there is significant gas accumulation, gas rushes out of the needle, making a hissing noise. In many cases, the horse visibly deflates over a period of 20-90 seconds.

The procedure does not appear to be particularly painful, as the skin is numbed by the local anesthetic. The actual penetration of the abdominal wall and intestine does not usually cause the horse to react much. But in many cases, I lightly sedate the horse for the procedure. This is mainly to keep the horse from moving around while the needle is in place.

I was taught to use an antibiotic injected through the needle as the needle is withdrawn. The antibiotic escapes into the same tissues that bacteria are tracked through. Theoretically, this should reduce the likelihood of infection of the peritoneal space and abdominal wall.

In many cases, a large release of gas and visible deflation of the horse means that the horse will feel better, at least for a time. Gas production by bacteria goes on regardless (the process of fermentation). If there is still a physical blockage downstream of the deflation site, then gas will re-accumulate over a period of time and the horse will again become visibly bloated and will return to pain.

If there is not a physical blockage but only a functional problem, then the colon may regain motility and begin transporting additional gas downstream.