Clinical Assessment of Adult Colic

Colic in horses may be an acute bout that either improves spontaneously or responds to medical or surgical intervention . Some horses suffer from chronic colic which pose a diagnostic delema for the medical clinician. In one study by Proudman (1991) only a small percentage (7%) require surgical intervention. Despite this low percentage of horses that would need surgery we as equine veterinarian are still are challenged as to which cases can be treated with medical therapy alone and which cases need surgical intervention. An early decision regarding the need for surgical therapy is essential. A delay in appropriate therapy increases the risk of a poor outcome. This talk will review the basics of the colic physical exam, ultrasonography, laboratory tests and pain management. Case examples will also be presented to help illustrate to the audience that the decision for medical or surgical treatment varies with each case.

Basic Physical Exam

Must assess the following for an abnormality to help determine the need for an exploratory laparotomy:

• Pain

• Cardiovascular Status

• Rectal Palpation

• Nasogastric reflux

• Abdominocentesis (If Warranted

Pain

Abdominal pain is usually associated with lumen distention, tension of the mesentery and/or ischemic injury. A simple obstruction will usually cause a low grade chronic pain which over time may wax and wane or slowly become worse as the degree of lumen distention increases. A large colon torsion or small intestinal volvulus which may cause rapid distention of the intestine as well as ischemic injury will cause unrelenting abdominal pain. Pain that is easily relieved by NSAIDS or Xylazine may respond to simple medical therapy. A short term response or incomplete response to pain medication is suggestive of a surgical lesion. Buscopan (N-butylscopalammonium bromide 20mg/ml- Boehringer Ingelheim) is an anticholinergic has been FDA approved in the management of gastrointestinal spasmodic colic. Unlike atropine, it has a very short plasma half-life concentration (15-25 min) and receptor acitivity. Animals that continue to colic through this medication (0.3mg/kg IV) in my experience are more likely to have a surgical lesion. Abatement of pain in the face of persistent depression and deterioration of the cardiovascular parameters (Cold sweat, cyanotic mucus membrane color, Full Body Tremors) may be associated with the presence of non-viable intestine, which is no longer painful due to disruption of its nerve supply. These cases warrant surgical exploration or euthanasia.

Cardiovascular Status

Cardiovascular (CV) compromise in the colic patient will be associated with the severity of the lesion. The CV status is assessed with the measurement of the heart rate, rhythm, pulse quality, 

mucus membrane color, capillary refill time and distal limb perfusion (Warm or Cold to palpation). Hypovolemic shock occurs secondary from a decrease in circulating blood volume that

occurs when extracellular fluid is sequestered in a third space such as a distended large colon or small intestine/stomach. Dehydration occurs in patients with hypovolemic shock when fluid is moved from the Intracellular Space‡Extracellular Space‡Lumen of the distended Bowel. In an effort to provide proper tissue perfusion the heart rate will increase.

Mucus membrane color and capillary refill time are very practical measurements that signal changes in the cardiovascular system. Mucus membrane color may initially with endotoxemic shock be a bright red color with a fast capillary refill time since the endotoxins will initially cause a hyperdynamic state (Increased HR with Capillary Vasoconstriction). As the bowel becomes more compromised then more endotoxins will enter into circulation . Various cytokines such as TNF and IL-1 are responsible for the hypodynamic shock phase. In this phase marked vasodilation occurs (Hypotensive Shock) which compromises peripheral perfusion and causing the darker (cyanotic) mucus membrane color and prolonged capillary refill time.

Rectal Palpation

Rectal palpation is one of the most useful diagnostic tests performed when evaluating horses with colic. A through knowledge of gross anatomical landmarks and familiarity with normal character of the viscera are important for determining the cause of colic. Remember that only about 25-30% of the abdominal cavity can be assessed with a rectal exam . The detection of displaced viscera, abnormal orientation of the taenia, edema of the intestinal wall and distention of viscera are abnormalities that may indicate a surgical lesion. In our referral hospital a rectal palpation combined with ultrasonographic evaluation are usually used together to reach a pre-operative diagnosis of colic.

Rectal evaluations are not without risk. Rectal tears are the most frequent reason for equine veterinary malpractice litigation. It has been suggested that primary factors causing rectal tears include failure of the rectal wall to relax, rectal straining, and patient resistance. A recent study (Luo and Bertone AAEP 2005) evaluated N-Butylscopolammonium Bromide and Lidocaine for control of rectal pressure. It was noted that N-Butylscopolammonium Bromide given at the labeled dose of 0.3mg/kg IV was able to significantly reduce the tension of the rectal wall within 1 minute of injection. No significant effects were noted when 50ml of 2% lidocaine was injected per rectum. This drug along with proper sedation may be of benefit when attempting to rectal a fractious horse. No adverse effects have been documented to the company when using this drug for a rectal exam. [...]