By: Shannel Cacho
Furosemide, more commonly known as “lasix” is a drug that is given to the majority of thoroughbred racehorses in the United States. This blog, however is not about lasix itself, but about the most common reason that it is used.
The purpose of furosemide is to prevent respiratory bleeding, which is referred to as exercise-induced pulmonary hemorrhaging (EIPH). When EIPH occurs, blood begins to enter the lungs and the presence of blood in the lungs can cause a pulmonary hemorrhage and ultimately lead to death in rare cases. Furosemide is administered to help reduce the occurrence and severity of EIPH.
EIPH is commonly seen in most racehorses and in other equine sports such as steeplechase and barrel racing, where strenuous exercise is performed for short periods of time. EIPH does not occur only in horses, it can also be seen in racing greyhounds and camels. When strenuous exercise is being performed it causes pulmonary vascular pressures to increase significantly, this also increases intravascular pressure at the level of the capillaries which can ultimately lead to stress failure of the pulmonary capillaries. When the capillaries rupture, blood can be introduced into the respiratory system.
The amount of blood present in the respiratory system can be correlated to a grading scale that was created by Dr. Kenneth Hinchliff, which has five different grades for EIPH. The scale ranges from 0 to 4. At the low end of the scale ‘0’ means that no blood is detected and ‘1’ means that there is a presence of a couple flecks of blood or two or fewer narrow and short streams of blood that is visible in the mainstream bronchi or trachea. On the upper end of the scale, a grade of ‘4’ means that there are several streams of blood that cover over ninety-percent of the tracheal surface and that blood is pooling at the thoracic inlet. Rarely a horse will be seen bleeding out of the nose after training or a race, and this is called epistaxis which is seen in approximately five percent of horses who have EIPH. Horses with epistaxis are automatically considered a grade ‘4’. Research has shown that horses with severe EIPH may have their performance affected, and ultimately have a shorten career.
How is EIPH diagnosed? EIPH is typically diagnosed via one of two methods, either via endoscopy or via bronchoalveolar lavage (BAL). An endoscopic evaluation should be performed within thirty to ninety minutes of exercise for the most accurate results, and it will provide conclusive evidence of blood in the airways. BAL is most accurate when done within thirty minutes of exercise, and this process is conducted by inserting an endoscope into the naris and infusing a buffered saline solution, which is then aspirated and analyzed via microscopy.
How can EIPH be prevented? The incidence and severity of EIPH can be helped by vigilant and virtuous management practices. Other than the use of fureosemide, nasal dilator bands can also be used to help reduce the severity of EIPH, due to the fact that it helps reduce intrapleural and alveolar pressure swings that directly contribute to capillary transmural pressure. The lower the intrapleural and alveolar pressure, the less stress that the capillaries will receive, which makes them less likely to rupture and cause bleeding into the respiratory system. When managed properly horses with low grades of EIPH can still have long and successful careers.