Exercise-Induced Pulmonary Hemorrhage 

There are no greater topics of debate in the horse racing industry than the use of race-day furosemide, also known as Lasix or Salix. This article is the first in a two part series detailing the reason why there is such high usage of the medication in the United States. However, before we can look into the controversy being the medication, let’s first look at what has sparked the need for its use in the sport.

Exercised-Induced Pulmonary Hemorrhaging, commonly known as EIPH or “bleeding”, is the condition in which the delicate capillaries in the lungs have ruptured when the horse is exercising at a high intensity. The bleeding may be localized to the area of the rupture or the bleeding could be excessive enough that it travels elsewhere in the respiratory system. EIPH is measured on a five level scale starting with Grade 0 to Grade 4:

Grade 0: no blood present
Grade 1: a minor amount of blood present in the trachea, a drop or two of blood OR one small stream
Grade 2: one long stream of blood OR two short streams of blood in the trachea
Grade 3: three or more distinct trails of blood present in the trachea
Grade 4: multiple trails of blood covering the vast majority of the trachea. Blood may be present at the nostrils, this is known as epistaxis

EIPH is not entirely understood by the veterinary community but there are several theories as to why it occurs. An extreme increase in vascular pressure is the most common, and perhaps the most likely of theories. As a horse works at high speed or intense exercise, the horse’s spleen pushes more red blood cells into the blood stream, increasing the pressure in the vascular system.  This phenomenon is known as “spleen dumping” and these extra oxygen-carrying blood cells can help the horse run faster and longer. The spleen, however, is not a main red blood cell producer (that is the job of bone marrow), but it collects blood and stores it. As oxygen-rich red blood cells flood the vascular system, the viscosity, or thickness, of the blood increases, stressing the blood vessels in the body. According to one study, it is thought that the red blood cells in the spleen can be abnormally shaped, possibly further hindering blood flow in an already flooded circulatory system. With the intense pressure in the system, smaller and more delicate capillaries in the lungs can burst under pressure, pushing blood into the respiratory tract.

EIPH is diagnosed with a visual inspection of the blood in the nostrils or a bronchoscope can be placed into the airway for a veterinarian to inspect and look for blood. Unfortunately, scopes are only able to reach the upper two-thirds of the respiratory tract and so blood may or may not be visible upon examination. If bleeding is suspected but no blood is present when viewed with the scope, a tracheal wash can be performed to identify red blood cells using a microscope. When a horse bleeds in a workout or in a race, the horse will suddenly “stop” running; as blood pools in the respiratory tract, the horse’s oxygen exchange becomes limited and he can no longer continue galloping at maximal effort. Blood can be found anywhere in the respiratory tract with it most commonly being found in the mid to upper trachea; rarely will horses come back with blood in the nostrils. It is not believed that EIPH is painful to the horse but it is considered to be uncomfortable.

It is believed that all horses, regardless of breed or sport, have the capability to bleed if they perform at maximal effort, mostly at speed. Some horsemen believe that EIPH has a genetic link and that some bloodlines are more prone to bleeding than others. It is possible that there might be some validity to the pedigree theory but bleeding is not something that can be “bred out of the breed”. Almost all racehorses will bleed to some degree and its occurrence may or may not affect his performance in a race or workout.

Once a known episode of bleeding has occurred, the alveoli, capillaries, and other affected tissues must be allowed adequate rest in order to heal. As bleeding episodes occur, the horse becomes increasingly more prone to additional and more severe bleeding episodes in the future. Non-steroidal anti-inflammatories as well as bronchodilators aid in the recovery process after a bleeding episode. Some horsemen believe that adding Vitamin C and bioflavenoids to a bleeder’s diet, can help heal the lungs but there is no scientific evidence to support this theory.