Gram-negative (one of the microorganisms that composes the large gut flora) bacteria in the horse's hindgut help break down fibrous feeds. Endotoxemia occurs when toxins from the wall of Gram-negative bacteria crosses the intestinal wall and gains access to the bloodstream. Endotoxin becomes concentrated on the surface of white blood cells, causing them to secrete inflammatory agents. Massive release of these agents cause the horse to go into endotoxic shock.

"Endotoxemia and sepsis (organisms or their toxins in the bloodstream) are major causes of mortality in the horse industry, causing significant economic losses," said Lucas G. Pantaleon, MV, MS, Dipl. ACVIM, who completed an endotoxemia study during his residency at the Virginia/Maryland Regional College of Veterinary Medicine's Marion duPont Scott Equine Medical Center in Leesburg, Va. "It is more commonly found in gastrointestinal disturbances such as colic, enteritis, or colitis."

The most common clinical signs of endotoxemia include abnormalities in mucous membrane color (darkened color), prolonged capillary refill time, increased heart and respiratory rates, reduced intestinal sounds, fever, and Hemoconcentration (increased concentration of cells and proteins in the blood).

Pantaleon said small volume resuscitation (SVR, use of 5 ml/kg of hypertonic saline solution plus 10 ml/kg Hetastarch) Hypertonic saline solution is a high sodium-containing fluid, and it is administered IV. The main function is to rapidly increase blood volume by drawing fluid from the tissues (interstitium) into the blood vessels. Because sodium is a very small molecule, it diffuses out of the vessels very quickly, thus the duration of action of hypertonic saline in this regard is short lived. Hetastarch is a synthetic colloid, also given IV that is composed by large particles. It also draws fluid from the interstitium, but since the particles are larger and they do not escape the vessels easily, the duration of action is longer.

Therefore, the combination of these two intravenous fluids as an additive had a longer-lasting effect than using each one individually. These fluids do not have a direct effect in blocking endotoxin. Cardiopulmonary effects had not been examined. He compared SVR to large volume isotonic fluid resuscitation (LVR, 60 ml/kg), and to a control group.

Use of LVR caused volume overload, and while the use of SVR did not reverse many of the negative cardiopulmonary effects induced by endotoxemia, horses treated with SVR "showed a trend toward less severe cardiopulmonary dysfunction during severe endotoxemia," said Pantaleon. Therefore, SVR treatment shows promise for endotoxemia treatment, however more studies need to be done.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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