Exercise-induced pulmonary hemorrhage (EIPH) is a common but concerning condition in which horses experience lung bleeding during exercise.¹ While it tends to be more prevalent in performance horses, it can occur in any horse during and after strenuous exercise. EIPH is considered a somewhat insidious condition; it often goes undetected by trainers and riders since it occurs deep within the lungs when smaller, fragile blood vessels in the lungs rupture under the mechanical stress of exercise.

During episodes of EIPH, the blood is often not seen because the amount of it in the airway is usually minimal.² In rare cases however, larger blood vessels can rupture, causing far larger amounts of blood to enter the airway and infiltrate upward into the nostrils. This is called epistaxis, which can be considered serious. If it goes unchecked and /or undetected, it can prove fatal.

Causes of EIPH in Horses

The available literature holds that if a horse engages in anything more than a slow canter, some blood vessels in the lung can rupture with the damage only affecting a small area.^2,3 With increased cantering, galloping and racing however, the damage can exacerbate and affect more of the lung. Occasionally, a racehorse will die during or shortly after a race. Upon necropsy, the lungs will be found to be swollen and dark red with blood. The lungs evidence a hemorrhagic rash with spots distributed uniformly across both lungs. The bronchi will be filled with pink foam.² This is a manifestation of extreme pulmonary edema. 

If the horse is not exercised to this degree and rested, it typically takes two to four weeks for the lungs to heal. Studies have shown that almost all exercising horses experience some degree of EIPH during intensive exercise, with 5% of horses showing blood at the nostrils.^1,3

It's common for many performance horses to show no visible signs of lung bleeding. In some horses however, symptoms may include: 

• Decreased performance
• Frequent swallowing 
• Coughing
• Extended cooling-out period³

There is also a potential for increasing and long-term damage if a horse: 

• Is galloped often
• Is worked on very hard or very soft surfaces
• Is forced to bear a great deal of weight³

Further, each incidence of EIPH contributes to the building up of scar tissue in the lungs, which increases the potential for future bleeding. 

Any obstruction of a horse’s airway reduces the flow of air it can take in, increasing the work it has to do to breathe and as well as the suction pressure applied to the tissues of the lung.⁴ The horse spends more energy to get less oxygen, and the internal pressure literally sucks fluid out of the lungs into the small airways, causing edema. Upper airway obstruction in racehorses is common enough to explain the high prevalence of EIPH in these animals, largely because the bit is a major cause of upper airway obstruction in horses.^2,4

EIPH Diagnosis

Lung bleeding can be detected by endoscopic examination. During the scoping, a long thin tube with a camera on the end is passed through the horse to view the upper airway and trachea.¹ Lung washes and bronchoalveolar lavage (BAL) are the most accurate method currently available to detect lung bleeding.^1-3 Blood in the lungs and lower airways has also been shown to be an irritant that can lead to further lung bleeding.⁴ The severity and frequency of lung bleeding in horses observed by scoping after exercise or racing almost always increase with age.² Endoscopic observation of blood in the airways 30 to 90 minutes after exercise can provide definitive evidence of EIPH.^1,4

Furosemide for the Treatment of EIPH

An American College of Veterinary Internal Medicine consensus statement declared that, based on the research done on EIPH in horses, there is high-quality evidence that furosemide is effective in the prophylaxis of this disease.⁴

Furosemide reduces the incidence and severity of EIPH in Thoroughbred racehorses. Horses with and without EIPH demonstrate equal improvements in race performance after administration of furosemide, indicating that the drug may enhance performance via mechanisms unrelated to EIPH.⁴

Where to buy Furosemide

Furosemide is available in the U.S. through several pharmaceutical manufacturers and through veterinary custom compounding companies. 

Furosemide carries numerous potential drug interactions. Please consult your veterinarian prior to beginning any treatment regimen.

FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.

¹thehorse.com.

²Varegg, M.S., Kløverød, K.M., Austnes, M.K. et al. Fatal pulmonary hemorrhage in a horse during bronchoalveolar lavage – single case report. BMC Vet Res 15, 169 (2019). 

³Merck Veterinary Manual.

⁴Hinchcliff, K.W., et. al. Exercise induced pulmonary hemorrhage in horses: American College of Veterinary Internal Medicine consensus statement. J Vet Intern Med. 2015; 29:743–58.