Todays respiratory case of heaves complicated by pneumonia. She is being treated with antibiotics, anti inflammatory medication and bronchodilators. RECURRENT AIRWAY OBSTRUCTION By Brian S. Burks, D.V.M., Dipl. ABVP, Board Certified Equine Expert foxrunequine Recurrent airway obstruction (RAO), also known as heaves or chronic obstructive pulmonary disease (COPD) can be a debilitating condition for many horses. As with many other diseases, early recognition and treatment are paramount to allowing your horse to have a useful and happy, long-lasting life; prevention is even better, albeit much more difficult. Lets begin with a brief introduction of respiratory function and anatomy. The lungs of your horse allow him or her to take in the large amounts of oxygen needed during exercise. Air is first warmed and humidified in the nostrils and pharynx. The latter also contains multiple lymphoid follicles (similar to tonsils) that respond to the various environmental antigens, i.e. pollens, to make antibodies. The larynx and the trachea are next- the trachea contains small finger-like projections called cilia; these cilia are used to move inhaled debris up and out of the lungs and trachea. The trachea divides into the mainstem bronchi, which divide to smaller and smaller bronchioles and finally to the alveoli, or air sacs, where gas exchange takes place ( oxygen is taken up by the red blood cells, and carbon dioxide is removed). When these structures become damaged due to viruses, bacteria, or chronic inhalation of particulate matter, this exquisite structure no longer functions properly. Clinical signs of RAO include exercise intolerance, nostril flaring at rest, coughing, purulent nasal discharge. Over time, a heave line develops along the edge of the ribs, representing the effort of expiration or breathing out (expiratory dyspnea). If the signs are severe, you may hear wheezing or other upper respiratory tract noises. The signs are often seasonal, at least at first, but when the damage begins to add up over time, there is no clinical remission during the cooler months. At least in the northern United States, clinical signs are often worse when the horse is housed indoors, even for a few hours. Thus, these horses are best kept at pasture with blanketing and a three sided shelter, rather than in a stall. Recurrent airway obstruction is rare in young animals, being a disease of middle age and older. It may, however, represent a continuum with another condition known as small airway inflammatory disease (SAID) that does occur in younger animals. The name RAO stems from the fact that the bronchioles and alveoli become intermittently plugged with mucus, with some alveoli becoming hyperinflated due to air trapping (alveolar emphysema). It is mainly, although not exclusively, an allergic condition, especially allergies to molds. Alternatively, viral infections may alter the structure and function of the pulmonary system, allowing for RAO to occur, and genetics may also be involved. Diagnosis of RAO in severe cases can be made on the basis of history provided by you, the owner, and the clinical signs shown by your horse; however, diagnostic aids are required to confirm the diagnosis and to diagnose those horses with less severe clinical disease. First and foremost, a good pulmonary exam, including the use of a plastic bag over your horses nose to make breathing deeper (rebreathing exam) should be performed by your veterinarian. This may allow expiratory wheezes to be heard, although wheezes may eventually also be heard during inhalation. Respiratory tract endoscopy is invaluable in the diagnosis of RAO. The endoscope may induce uncontrollable coughing and allow visualization of inflammation and exudate in the pharynx, trachea, and bronchi. Bronchoalveolar lavage may also be performed to evaluate cells from the lower airways; the primary cell is the neutrophil, a type of white blood cell. This is different from other equine diseases, and human asthma, in which the eosinophil, another type of white blood cell is more prevalent. Transtracheal washes allow for sterile culture collection to determine if there is underlying infection. Radiographs, or x-rays, of the thorax must be performed in a hospital setting due to the size of the machine required. These radiographs often show mixed patterns in the lungs. One of the main lesions noted is bronchiolitis, in which these small airways are thickened and more prominent compared to normal. They also determine if there is a focal lesions or a miliary pattern which may be associated with other disease processes. Since the primary function of the lung is gas exchange, an arterial blood gas sample may be obtained. Again this is best done in a hospital setting, as this sample must be run within a few minutes. This test may show impaired oxygen and carbon dioxide exchange within the alveoli. In the near future, a practical method of lung function testing should also become available. Treatment is aimed at prevention of exposure to the cause. This entails ensuring good ventilation of barns, and removal of dust, cobwebs, and hay from the barn. Since this is impractical in many situations, 24 hour turn out is most desirable. When horses are fed in the pasture, round bales should NOT be used, as the mold content is usually higher, and will increase over time as the bale is exposed to inclement weather. Also, horses must stick their noses deep into the round bale, thus inhaling large amounts of dust and molds. Sometimes hay must be removed completely from the diet, substituting complete feeds such as Purina Complete Advantage or Triple Crown Forage; other possibilities include alfalfa pellets or haylage. If your horse must be stalled for even part of the day, it is important to remove all hay bales and straw from the area; bedding should be on shavings, or even shredded paper. Therapeutic intervention may be necessary, but should ALWAYS be combined with management changes. Recurrent airway obstruction is characterized by inflammation, thus the use of anti-inflammatory medications is indicated. This is usually in the form of corticosteroids such as dexamethasone; however their use can be associated with side affects such as gastric or colonic ulceration, muscle wasting, depression, and a long, dry hair coat. Excessive drinking and urination may also be noted. The systemic affects of corticosteroid use can be minimized by using local deposition into the lung via inhalant methods, such as the Equine AeroMaskJ from Trudell Medical International. Airway constriction is also noted during RAO, and thus the use of bronchodilators is often indicated. Systemically, they may only be used for short periods of time, and may be associated with sweating and agitation in some horses. Again, these medications may also be inhaled, minimizing the systemic affects. Other therapies include cromolyn sodium as an inhaled medication and allergy desensitization. Immunotherapy is fraught with the difficulty of diagnosis. In humans skin testing is used to determine which antigens are allergenic; however, in the horse some normal horses will also have skin reactions. Serum testing for allergies has been developed, but again some normal horses will have positive testing and some affected horses will not respond to allergy shots (desensitization). Treatment of other disease conditions such as bacterial pneumonitis and Equine Cushing=s Disease, as well as good husbandry (vaccination, deworming) also help to treat and prevent RAO. In conclusion, I hope that you will recognize the sometimes subtle signs that your horse may exhibit, allowing early intervention, thus providing you with many years of enjoyment with your best friend, your horse. Prevention of RAO, while difficult, is still the best available treatment. This includes avoidance of molds and other allergens whenever possible. Since viruses may also cause RAO, good nutrition is paramount in providing your horse with an immune system capable of fighting viral and bacterial infection. Effective medications do exist, but the best use of them is by direct deposition into the lung via inhalation. Currently, this is accomplished by the Equine AeroMaskJ, although newer, less expensive methods are soon to be available. Allergy treatment can be a useful adjunctive therapy. Dr. Brian Burks is the directing veterinarian at Fox Run Equine Center, a 24-hour medical-surgical center near Pittsburgh, Pennsylvania. Dr. Burks was an intern and then a resident in equine internal medicine. He is a Board Certified Equine Expert, by the American Board of Veterinary Practitioners. For additional information, please visit foxrunequine Fox Run Equine Center foxrunequine
Posted on: Mon, 18 Aug 2014 23:00:00 +0000
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