Asthma is a recurring respiratory compromise featuring the constriction of the lung’s airways. First, excess mucus forms, the airway walls swell with inflammation and can actually ulcerate, and finally the airway muscles go into spasm leading to constriction. Airway constriction leads to inability to draw a deep breath, intolerance to exercise, coughing, and musical sighing sounds called “wheezes,” though not all these symptoms may be apparent at the same time. Sometimes a low-grade chronic cough is the only manifested sign but it should be remembered that an acute asthmatic crisis can arise at any time and can represent a life-threatening event. Asthmatic airway constriction can happen spontaneously or as a type of allergic reaction. When it comes to treatment, relieving and preventing airway constriction is what it is all about.
Because of the constricted airways, the actual volume of air this patient can move in and out of the lungs each breath is reduced. There is often a great deal of effort seen in the cat’s breathing. The abdomen appears to be working to push air out and the breaths are shallow and rapid. The cat may even be breathing with its mouth open in an effort to move the largest possible amount of air. The next step toward making a diagnosis of feline asthma is the chest radiograph. Classically, this radiograph will show what is called “air-trapping.” This means that the small airways have constricted such that inspired air cannot be exhaled. The lungs are larger in appearance than normal as they are over-inflated. The diaphragm may seem flattened due to this over-inflation.
It is crucial to realize that the underlying problem in the airway is inflammation. Inflammation is what is responsible for the constriction. To resolve the inflammation, corticosteroid medications have been the cornerstone of therapy. These can be given orally, by injection, or more recently via metered dose inhaler. Usually treatment is started with either an oral corticosteroid or a long-acting injection (such as depomedrol). These medications are relatively inexpensive and a good response to them helps confirm the diagnosis, as mentioned. Nebulisation is done with an inhaler at one end and a face mask on the other. The inhaler is actuated into the spacer and the infant simply breathes in the spacer’s contents. Corticosteroid inhalers, being the most popular, are typically used twice daily long term while airway dilator inhalers such as albuterol-containing Proventil® or Ventolin® are used for flare-ups. Cats are generally started on a combination of oral prednisone and the metered dose inhaler and gradually maintained on only the metered dose inhaler.