Summary
Many cases of abdominal pain (colic) resolve with nothing more than a little time or treatment. A majority of colic cases resolve with medical treatments performed by your vet in the field. Although field treatments are somewhat limited in scope, they are often very helpful in treating simple intestinal conditions like spasm or gas accumulation.
A small minority of horses experiencing colic pain require intravenous fluids or intensive care in a hospital setting, and only a very small percentage require surgery. But it is critical that these cases are promptly diagnosed so that the horse can be transported to a hospital for treatment.
Ideally, upon arrival, your vet performs diagnostics that enable them to reach a diagnosis. They take a history and perform a physical exam before any treatments are performed. This allows your vet to gather baseline physical exam findings before the effects of any medication complicate this assessment. The degree of pain a horse is experiencing is an important parameter, preferably evaluated before treatment with pain relievers.
However, if a horse is experiencing severe colic pain it might not be possible to safely perform these initial diagnostics without first controlling pain with medications. An early step in symptomatically treating horses that are actively demonstrating colic pain is the use of pain-relieving medication such as flunixin meglumine (Banamine®) or n-butylscopalammonium chloride (Buscopan®). Violently painful horses may need to be given powerful sedatives and narcotic type pain relievers to allow safe examination.
If you have already given a horse any medications or provided any other treatments to your horse you MUST tell your vet so they can interpret the horse's clinical findings with these additional factors in mind. Banamine, for example, effectively masks signs of abdominal pain often leading to a false sense of confidence that the colic episode has ended or resolved.
After taking a history, performing a physical exam and possibly providing pain relief, your vet may recommend that they perform additional diagnostics to reach a diagnosis. This may include a rectal exam or nas-gastric intubation, among others.
In "tubing", as it is called, a naso-gastric tube is usually passed into the horse's stomach as a diagnostic and for treatment. If there is no reflux (fluid back from the stomach when the tube is passed and after a siphon is created to try to pull fluid out), then the vet may elect to administer fluid through the tube. This fluid distends the stomach and stimulates the gastro-colic reflex, which stimulates the downstream intestine to move. This reflex effect is probably more important than any direct laxative effect of fluids given by stomach tube. It is also probably more important than the choice of fluids administered.
In horses that have severe gas distention of the colon and cecum, some vets decompress (deflate) the segment of intestine in the field using a large needle through the flank. I usually only do this in horses for which continued treatment in the field is the only option (not surgery). It can be a very helpful procedure where the colon or cecum is severely bloated and not functioning.
The horse is then monitored for response to treatment. In most cases, horses improve while your vet is at the farm. If the horse is persistently painful following treatment, your vet may stay until they are comfortable, and their vital signs provide some indication that the colic episode will resolve.
In some cases, your vet may choose to give additional doses of pain relieving medications. However, horses that do not respond to initial or subsequent field treatments may need to be hospitalized so that more advanced diagnostics and treatments can be performed.