Your racehorse stops at the top of the lane and slows to a crawl coming home. He may cool out slowly and may not drink water after the race. He may cough or snort and swallow while cooling out. Or he may have fresh red blood trickle out his nose. These are all common findings after a race when a horse “bleeds” from the lungs during a race. We all know that racehorses commonly “bleed,” but eventing horses and other types of speed competition horses like barrel racers also "bleed." Even racing greyhounds and some elite human athletes bleed from the lungs during exertion. For that matter, studies have shown that almost all racehorses bleed, and most event horses bleed. Have you ever wondered why and exactly what goes wrong when they bleed? What about the best treatments/adjuncts? In this article, I'll try to answer some of your questions about this very frustrating malady.
What is “bleeding” or Exercise Induced Pulmonary Hemorrhage (EIPH)?
The lungs are specialized organs for oxygenating blood. The structure of the lungs are like a tree, with the trachea as the trunk, the bronchi as the branches and the tiny microscopic alveoli as the leaves. The tiny sac-like balloons of the alveoli are lined with tiny blood vessels (capillaries). It is across these capillary cells that oxygen enters the body and carbon dioxide is expelled. Each heart beat sends freshly oxygenated blood to the working muscles and the same amount of spent blood to the lungs to be recharged. During breathing at rest, the hemoglobin in the red cells is fully (100%) saturated as it passes through the lungs. During exercise in horses, the blood is traveling so fast that after passing through the lung, the blood is only partially oxygenated. Blood pressure increases both in the body to keep pace with the demand from the exercising muscles and in the lungs to get the same volume of blood through the lungs. This pressure ultimately breaks some of the capillaries causing loss of blood into the alveolar space. When enough capillaries break, the blood drains down the bronchi and into the trachea. The diagnosis is made by looking in the trachea for evidence of blood called endoscopy or “scoping.” EIPH occurs in just about all racehorses at some time or another.
How is EIPH prevented?
The first line of prevention of EIPH is Lasix (Salix, furosemide). Lasix is a diuretic that decreases plasma or blood volume which results in decreasing the blood pressure in the pulmonary (lung) circulation. It is a fine line between losing plasma volume necessary for preventing EIPH and losing so much that critical blood pressure to the muscles is decreased. Recently, Lasix has been proven beyond any doubt to prevent bleeding in racehorses.
The next group of drugs for preventing EIPH are the antifibrinolytic drugs Amidocarb (Amicar) and Tranexamic acid (Tranex). When a capillary breaks, the underlying exposed collagen stimulates platelets to collect and substances in the blood called clotting pro-factors to become activated, forming a clot. Part of the normal process in the clotting cascade is the simultaneous breakdown of that clot, called fibrinolysis. During exercise, both clotting and fibrinolysis are increased, as blood is recruited to sustain blood pressure. Amicar and Tranex prevent fibrinolysis, allowing the normal clotting process to seal the broken capillaries. Recent studies on Amicar actually increased racing times, indicating some interference with performance, which makes it a bleeding drug that should only be used if absolutely necessary.
Kentucky Red (Carbazochrome Salicylate) works by stabilizing the capillary membranes, preventing breakage. This is also the mechanism of action of vitamin C and bioflavonoids (including hesperidin), common supplements used for bleeding.
Estrogens (Premarin, estradial cyprionate or ECP, estrone sulfate) may have more than one mechanism. The primary function of estrogens is to increase platelet aggregation at the site of a capillary breakage. However, estrogen also has antifibrinolytic effects, similar to Amicar and Tranex.
Vitamin K is also commonly administered to prevent EIPH. Vitamin K is an important co-factor for several proteins in the clotting cascade.
Finally, a commonly used Chinese Herbal product called Yunnan Bai Yao can be used to prevent EIPH. This product shortens clotting times, and may have direct effects on platelets, similar to estrogen. There are numerous other herbal treatments, which may be administered daily for the purpose of strengthening capillaries, improving clotting function and oxygen exchange.
Flair ® nasal strips have actually been shown to decrease the severity of bleeding also. These products have the ability to hold the nostrils open, decreasing the work required by the horse to breathe.
My Horse Bled in a race, now what?
Bleeding is the result of capillary damage in the lungs. This is a similar injury to a bruise and can be as serious as a large hematoma. It takes at least 10 to 14 days for a bruise to reorganize and heal, and that is the same time frame that the lungs require to heal. If the horse is raced or does other speed work too soon after a significant bleeding episode, it is the equivalent of reinjuring a bruise or hematoma. The end result is a more significant injury that will take even longer to heal. Repeated trauma to the lungs has the same result as repeated trauma anywhere else: the tissue is unable to heal completely resulting in scar tissue formation. Scar tissue in the lungs cannot contribute to oxygen exchange, and is less flexible, making further episodes of bleeding more likely. Lung rest is the most important factor in recovering from EIPH.
The blood in the airways traps mucous and bacteria, so treatment for a horse that has bled includes bronchodilators to open the airways, most commonly Ventipulmin, and antibiotics to prevent a lung infection. Usually Ventipulmin is administered for 10 days to clear out blood and mucus in the airway, and antibiotics are administered for 7 days to prevent infection. Ideally, after a significant bleeding episode, it takes a full three weeks for a complete recovery.