Equine Flash Notes - Recurrent Airway Obstruction

Question 1

what is the classic signalment of a horse with RAO?

Answer 1

mature horses over 7 years old with no sex predilection with exposure to organic dust, molds (poorly cured hay), mites, & endotoxins

Question 2

what is the etiology of RAO? how is it diagnosed?

Answer 2

recurrent allergen induced neutrophilic inflammation of lower airways - diagnosed by thoracic auscultation, BAL with non-degenerate neutrophils, curschmann’s spirals (can’t differentiate between IAD with this), arterial blood gas, bronchodilator test, endoscopy, & pulmonary function testing

Question 3

what are 4 ways to treat & prevent recurrence of RAO?

Answer 3

minimize allergen exposure, control airway inflammation, relieve airflow obstruction, & environmental changes

Question 4

what is the primary difference between RAO & IAD?

Answer 4

only definitive difference from IAD is tachypnea at rest with RAO - not with IAD

Question 5

what is the pathogenesis of RAO?

Answer 5

recurrent allergen induced neutrophilic inflammation of lower airways - diagnosed by thoracic auscultation, BAL with non-degenerate neutrophils, curschmann’s spirals (can’t differentiate between IAD with this), arterial blood gas, bronchodilator test, endoscopy, & pulmonary function testing

Question 6

horses in what geographic locations are more commonly affected by RAO?

Answer 6

northern USA, europe - primarly stabled horses, & southeastern USA more prevalent in horses on pasture in the summer & fall

Question 7

what is the most important component of treatment for a horse with RAO?

Answer 7

environmental changes

Question 8

what is the goal of treatment for a horse with RAO?

Answer 8

minimize allergen exposure, controlling airway inflammation, & relieving airflow obstruction

Question 9

what is heard on thoracic auscultation in a horse with RAO?

Answer 9

at rest & with rebreathing bag - expiratory wheezes, crackles, & tracheal rattle

Question 10

what is seen on arterial blood gas analysis in a horse with RAO?

Answer 10

hypoxemia (decrease PaO2) & increased PaCO2 in chronic cases

Question 11

what do you expect results on a bronchodilator test to be in a horse with RAO?

Answer 11

after administration of atropine, marked imrpovement in signs observed within 10 minutes

Question 12

what results do you expect on pulmonary function testing in a horse with RAO?

Answer 12

treadmill with endoscopy - decreased airway compliance, increased pulmonary resistance, & increase in transpulmonary pressure during respiration

Question 13

what is seen on endoscopy in a horse with RAO?

Answer 13

excessive mucopurulent tracheal exudate

Question 14

how is pasture associated heaves treated?

Answer 14

change to a different pasture or move the horse indoors to a well ventilated stall

Question 15

how is heaves associated with an indoor environment treated?

Answer 15

complete turnout is critical

Question 16

what steroids are used for treating RAO?

Answer 16

oral prednisolone, parenteral dexamethasone for respiratory distress horses, & inhaled steroids such as fluticasone or nebulized dexamethasone

Question 17

what is the benefit of using bronchodilators for horses with RAO?

Answer 17

relaxes smooth airway muscle - can use oral or inhaled b-2 agonists, and for emergency relief, atropine (anticholinergic)

Question 18

what is the classic history of a horse with RAO?

Answer 18

signs that recur & wax/wane in response to season, specific food/allergen exposure

Question 19

what are the clinical signs associated with RAO?

Answer 19

afebrile, exercise intolerance, coughing during exercise, exaggerated end-expiratory effort in a resting horse, mucopurulent discharge, & heave line