Etiology and Pathogenesis of Exercise-induced Pulmonary Hemorrhage in Horses
EIPH occurs in most racehorses and in many other horses used in equine sports (eg, polo, barrel racing, eventing) that require strenuous exercise for short periods of time. The prevalence of EIPH varies according to breed and method of diagnosis. Epistaxis is seen in a small proportion (~5%) of horses with EIPH. Blood in the tracheobronchial tree is identified in 45%–75% of racehorses via endoscopic examination, and hemorrhage is detected by cytologic examination of bronchoalveolar lavage in > 90% of racehorses. Thoroughbred racehorses are diagnosed more frequently than Standardbred racehorses. EIPH is also fairly common in barrel racing Quarter Horses (~60%). A heritable component to EIPH is suspected in Thoroughbreds. Increased prevalence of EIPH in older horses is attributed to a longer racing career and repeated capillary damage in the lungs. Racing at lower ambient temperatures may increase the risk of EIPH.
The proposed pathophysiologic mechanism for pulmonary hemorrhage includes high pulmonary pressures during maximal exercise, with resultant remodeling of pulmonary vein walls, increased intravascular pressure at the level of the pulmonary capillaries, and subsequent rupture of the capillaries with extravasation of blood into the pulmonary interstitium and alveoli. Repeated hemorrhage may result in chronic inflammation and fibrotic changes.
Differential diagnoses for detection of blood within the upper or lower airways include: ethmoid hematoma, guttural pouch mycosis Guttural Pouch Mycosis Guttural pouch empyema is defined as unilateral or bilateral accumulation of purulent exudate in the guttural pouch. The infection usually develops subsequent to a bacterial (primarily Streptococcus... read more , fungal granuloma, pulmonary abscess or pneumonia, trauma, foreign body, or neoplasia.
Diagnosis of Exercise-induced Pulmonary Hemorrhage in Horses
Cytologic analysis of BAL fluid
Clinical signs of EIPH may include poor performance and epistaxis. Rarely, sudden death is reported. Epistaxis is rare in horses with EIPH and poor performance is a nonspecific clinical indicator. Endoscopic observation of blood in the airways 30–120 minutes after exercise provides definitive evidence of EIPH. Other sources of hemorrhage in the upper airway (guttural pouch mycosis Guttural Pouch Mycosis Guttural pouch empyema is defined as unilateral or bilateral accumulation of purulent exudate in the guttural pouch. The infection usually develops subsequent to a bacterial (primarily Streptococcus... read more , ethmoid hematoma Ethmoid Hematoma The paranasal sinus system of the horse consists of paired frontal, conchal (dorsal and ventral compartments), sphenopalatine, and maxillary (rostral and caudal compartments) sinus compartments... read more ), must be excluded during endoscopic examination. Evidence of bleeding may be detectable by endoscopy for 1–3 days after exercise. A bronchoscopic grading system (0–4) exists to evaluate the severity of EIPH.
If EIPH is suspected and the horse cannot be examined within a reasonable time after exercise, cytologic examination of bronchoalveolar lavage fluid for assessment of RBCs and hemosiderophages is diagnostic. Cellular evidence of hemorrhage can be detectable for several weeks after a bleed. Stains that highlight iron-containing pigments (Prussian blue) facilitate recognition of these cells. Thoracic radiography may demonstrate alveolar or mixed alveolar-interstitial opacities in the caudodorsal lung fields; however radiography and ultrasonography are of little diagnostic value for EIPH.
Treatment and Control of Exercise-induced Pulmonary Hemorrhage in Horses
Although its use is controversial, the administration of furosemide before racing reduces the incidence and severity of EIPH in Thoroughbred racehorses. Regulatory issues surround the use of furosemide and it is banned in many racing jurisdictions outside of the US.
Evidence for the efficacy of other strategies aimed at preventing EIPH is weak. Application of nasal dilator bands has been associated with a reduction in RBC counts in BAL fluid after exercise, however there is little high quality evidence that these strips can decrease severity of EIPH in exercising horses.(1 References Exercise-induced pulmonary hemorrhage (EIPH) is defined as detection of blood in the airways of horses after strenuous exercise. Epistaxis is rarely detected; however, identification of blood... read more ) Alternative treatments, including procoagulant agents (eg, vitamin K, conjugated estrogens, aminocaproic acid), antihypertensive drugs, rheologic agents (pentoxifylline), bronchodilators, prolonged rest, dietary supplements (hesperidin-citrus bioflavonoids), and anti-inflammatory drugs, have not demonstrated therapeutic benefit.
EIPH is highly prevalent in Thoroughbred racehorses and other horses participating in strenuous exercise.
Rupture of the pulmonary capillaries and subsequent hemorrhage into the alveoli causes EIPH.
Epistaxis associated with EIPH is rare and its absence should not be used to rule out this condition.
Treatment with furosemide before racing provides reduces the frequency and severity of bleeding; however, its use is highly controversial for the treatment of EIPH.
Hinchcliff KW, Couetil LL, Knight PK, et al. Exercise induced pulmonary hemorrhage in horses: American College of Veterinary Internal Medicine consensus statement. J Vet Intern Med. 2015 May-Jun;29(3):743–758.
For More Information
Hinchcliff KW et al. Exercise induced pulmonary hemorrhage in horses: American College of Veterinary Internal Medicine consensus statement. J Vet Intern Med 2015; 29:743–58.
Crispe EJ & Lester GD. Exercise induced pulmonary hemorrhage: Is it important and can it be prevented? Vet Clin North Am Equine Pract. 2019; 35:339–350.
Also see pet health content regarding exercise-induced pulmonary hemorrhage in horses Exercise-induced Pulmonary Hemorrhage in Horses Exercise-induced pulmonary (lung) bleeding occurs commonly in racehorses and is observed in horses used for other sports (such as polo, barrel racing, and 3-day events) that require strenuous... read more .