EIPH: Tracheobronchoscopic Assessment of Severity, Identification of Risk Factors, and Association with Performance

Exercise-induced pulmonary hemorrhage (EIPH) is a condition with high prevalence in racing Thoroughbreds. However, despite its perceived importance as a cause of morbidity and impaired performance, few studies have attempted to address the relationship of EIPH to race performance and there has been no formal investigation of risk factors for development of EIPH. Determination of the clinical importance of exercise-induced pulmonary hemorrhage depends on the availability of suitable means of documenting presence and severity of hemorrhage. Severity of hemorrhage has traditionally been assessed visually during tracheobronchoscopic examination of horses soon after racing but the inter-observer variability of the visual grading system has not been evaluated. The purpose of this report is to describe a system for grading severity of EIPH by endoscopic examination, use this system to investigate risk factors for the development of EIPH, and explore the relationship between the grade of EIPH with performance.

Tracheobronchoscopic examinations were performed on Thoroughbred horses within 2 hours after completing a race in Victoria, Australia. Races were 1000 to 3200 meter flat races run on turf in Melbourne, Australia between March 1 and June 18, 2003. Each examination was recorded on videotape for subsequent review. The videotaped examinations were independently reviewed by 3 veterinarians (JB, AD, KH), and the severity of EIPH was graded according to a modification of a previously described system which had 4 grading levels, whereas the current modification has 5: Grade 0 - no blood detected in the pharynx, larynx, trachea, or main stem bronchi visible from the tracheal bifurcation; Grade 1- presence of one or more flecks of blood or = 2 short (less than one-fourth the length of the trachea) narrow (<10% of the tracheal surface area) streams of blood in the trachea or main stem bronchi visible from the tracheal bifurcation; Grade 2- one long stream of blood (more than half the length of the trachea) or >2 short streams occupying less than one-third of the tracheal circumference; Grade 3 - multiple, distinct streams of blood covering more than one-third of the tracheal circumference and no blood pooling at the thoracic inlet; Grade 4 - multiple, coalescing streams of blood covering >90% of the tracheal surface with blood pooling at the thoracic inlet.

Eight hundred and fifty endoscopic examinations were performed on 747 Thoroughbred race horses. Prevalence of EIPH, defined as blood in the trachea or bronchi detected by at least one observer, was 68.4%. Severity scores were identical for all 3 observers for 68.9% of examinations. Scores of 2 of the 3 observers agreed, and that of the third observer differed by 1 grade, in 30.6% of examinations. Scores of 2 of 3 observers agreed and that of the third observer differed by = 2 grades in 0.3% of observations. All 3 observers disagreed in 0.2 % of examinations. Therefore, all observers agreed or 2 of 3 agreed with the third differing by = 1 grade in 99.4% of observations. Kappa statistics for concordance between pairs of observers were 0.76, 0.80, and 0.75.

Endoscopic examinations were performed on 744 horses that met criteria for inclusion in the study, representing 52.1% of those eligible horses starting during the study period. Both presence of EIPH and its severity were significantly (P <0.05) associated with race performance. Horses with EIPH, defined as grade 2 or higher, were 4.0 times less likely to win, 1.8 times less likely to finish in the top 3 places, and finished 1.8 meters farther behind the winner than did unaffected horses. The severity of EIPH (grade 0 - 4) was significantly associated with reduced probability of winning, slower horse speed, and greater length behind the winner. Horses with grade 4 EIPH finished an average of 3.4 meters farther behind the winner than horses of grade 0.

Risk factors examined included those intrinsic to the horse (age, sex, weight carried, age at first start, number of starts as a 2 year old, time from previous start, time from next-to-last start, lifetime earnings, wins, seconds, thirds, presence of dirt in the pharynx or trachea, excess tracheal mucus), environmental factors (wind speed, ambient temperature, humidity, rainfall, dew point, and concentration of nitric oxide, carbon dioxide, sulphur dioxide and particulate matter in air), and race factors (track, trainer, track condition, penetrometer reading, distance raced and time between start of race and endoscopic examination).

Exercise-induced pulmonary haemorrhage was significantly associated with the time between the start of the race and examination, age at first start, presence of excess tracheal mucus or tracheal dirt and concentration of airborne particulate matter. Age, sex, weight carried and race distance were not significantly associated with presence of EIPH.

The results of the current study demonstrate that it is possible to achieve a high degree of concordance among experienced investigators for assessment of severity of exercise-induced pulmonary hemorrhage in Thoroughbred race horses. This study validates the use of a subjective scoring system, thereby providing a tool with which to investigate the causes and effects of EIPH.

Factors previously reported in smaller studies in North America as associated with EIPH were not identified as such in the current study. That both tracheal mucus and tracheal dirt were associated with EIPH suggests a role for airway inflammation or obstruction in development of this condition.

EIPH was associated with poor performance. The strength of this association and its consistency across 3 measures of performance, combined with experimental and observational evidence of the negative effect of EIPH or blood in airways on exercise performance on a treadmill, blood gas tension, and pulmonary function, support a conclusion that EIPH is a cause of impaired performance in horses not medicated with furosemide or wearing nasal dilator strips.