There are two major reasons horses with colic may require fluid therapy: hypovolemia and endotoxemia (or sepsis). Hypovolemia results from decreased intake, loss of fluid (typically sweat or reflux), and sequestration of fluid (typically in horses that have intestinal obstruction).
Strangulation obstruction of the small intestine is frequently fatal because of simultaneous occlusion of the intestinal lumen and its blood supply, resulting in progressive necrosis of the mucosa, and development of endotoxemia. Among the more common causes of this condition are strangulating lipomas and entrapment within a natural internal opening or a mesenteric defect.
Small colon impaction is a relatively infrequent cause of colic. However, when it does occur, it can be difficult to recognize and to manage. We have noticed over the last several years that many of these cases are initiated by diarrheal disease, making the eventual diagnosis of an obstructive condition unexpected by the veterinarian.
Simple obstruction: an obstruction of the intestinal lumen without compromise to the blood supply. However, fluid is continually secreted into the small intestine and is not absorbed. As the intraluminal pressure increases intestinal mucosal capillaries are compressed.
Although there has been a substantial increase in our understanding of postoperative complications in recent years, the treatments remain very much the same. For ileus, these treatments include decompression of the stomach, replacement of fluid and electrolyte losses with parenteral fluids, and use of a variety of prokinetic agents. For adhesions, treatments include anti-inflammatory medications and antibiotics, although some of the newer physical agents such as carboxymethylcellulose offer new modalities for combating this problem.
There are other agents in each of the above categories, but these drugs can be used as examples in order to develop a treatment plan. For a horse that is actively showing signs of colic, an abbreviated physical examination (heart rate, mucous membrane color, and capillary refill time) should be performed before administering an analgesic.
Generally, horse owners are astute at detecting signs of colic. These may include subtle not being enthusiastic about coming up from the field in the morning, not showing interest in other horses and people, or not finishing their feed. These signs should be taken seriously because in a number of occasions, these are the first signs of colic.
In horses with primary cecal impactions, there is a gradual onset of abdominal pain similar to the development of a large colon impaction. The typical time course is 5-7-days. During this time, veterinarians may use treatments for impactions, such as intravenous administration of analgesics and nasogastric administration of laxatives such as mineral oil, dioctyl sodium sulfocuccinae (DSS) or magnesium sulphate (Epsom salts).