During colic surgery, it can be difficult to judge whether twisted bowel deprived of oxygenated blood, a process called ischemia, will recover sufficiently once it is replaced and blood flows again. While the bowel might look healthy on the outside, the internal surface might have suffered great damage, causing it to malfunction once reperfusion occurs (blood flow is restored). This malfunction can lead to significant postoperative complications and even death.

Recently, a study from the University of California, Davis, was conducted to design a laboratory model using a living piece of equine small intestine. The intestine was kept alive in culture within a circuit of machinery so it could be subjected to ischemia and reperfusion in an effort to better understand this disease process.

One of the researchers, Jack Snyder, DVM, PhD, Dipl. ACVS, chief of equine surgery at the UC Davis Veterinary Medical Teaching Hospital and director of the UC Davis’ new equine physical therapy program, described how sections of small intestine were connected to what’s called an isolated perfusion circuit. "We have a specific computer program and pumps that work with the intestine" to keep blood and other fluids flowing in and out normally, "like a heart-lung machine," he said. Groups of intestinal segments were exposed to various time periods of ischemia followed by an hour of reperfusion. Additional sections of intestine were kept on normal blood flow for comparison. Each intestinal section was then exposed to a solution of albumin to study the effects of ischemia. Albumin is a relatively large protein (72 angstrom in diameter) compared to the size of what normally crosses the intestinal mucosa (6 angstrom in diameter). Snyder explains, "As damage occurs in the intestine, permeability increases, allowing proteins to move from the vascular space into the intestinal lumen."

The data indicated that as the amount of ischemia increased, the integrity of the lining of the intestine decreased, and more albumin crossed the mucosal barrier. The team of researchers speculated that this might have been the result of oxygen-free radical damage occurring during reperfusion. Studies in other species have shown that free radicals build up when circulation is temporarily cut off. Once blood flow is restored, free radicals damage cells, particularly those lining blood vessels. Other studies have shown that nitric oxide donors–molecules that trap free radicals–lessen this damage in the intestine. This information might help researchers find other drugs that can protect horses from reperfusion injury after colic surgery