Treating feline bronchial disease
Q: What is the standard of care for cats diagnosed with bronchitis or asthma?
A: Dr. Philip Padrid gave an excellent lecture entitled "Inhaled steroids to treat feline lower-airway disease: 300 cases 1995-2007" at last year's American College of Veterinary Internal Medicine (ACVIM) Forum in San Antonio. Here are some relevant points from it:
Chronic bronchial disease in cats occurs most commonly as chronic bronchitis and asthma. Chronic bronchitis is defined as an inflammatory disorder of the lower airways that causes a daily cough, for which other causes of cough (including heartworm disease, pneumonia, lungworms and neoplasia) have been excluded. Asthma is more loosely defined as a disorder of the lower airways that causes airflow limitation, which may resolve spontaneously or in response to medical treatment.Airflow limitation generally is the result of some combination of airway inflammation, accumulated airway mucus and airway smooth-muscle contraction. The signs of asthma can be dramatic, including acute wheezing and respiratory distress. Sometimes, however, the only sign of asthma-induced airflow limitation is a daily cough.
Definitive diagnosis of asthma usually is based on specific pulmonary function studies that require a cat's cooperation. Because both disorders, bronchitis and asthma, can cause a daily cough as the only clinical sign, there are many times when it is not possible to distinguish bronchitis from asthma in the cat. Nevertheless, the diagnosis, prognosis and treatment options for both diseases overlap with great frequency.
Inhaled corticosteroids and broncho-dilators have been formally recommended to treat cats with bronchial asthma since at least 1993. Since then, a number of articles have demonstrated the clinical effectiveness of fluticasone for treatment of cats with allergic rhinitis, bronchitis and asthma. There have been no controlled published studies to determine the optimal dose or interval for use of fluticasone in cats.
Aerosol administration of the medications to cats relies on delivery of drugs to the distal airways, which in turn depends on the size of the aerosol particles and various respiratory parameters, such as tidal volume and inspiratory flow rate. Recent published studies in cats have demonstrated that passive inhalation through a mask and spacer combination is an effective method of delivering sufficient medication to be clinically effective.
Drugs for inhalation typically come in a rectangular-metered dose inhaler (MDI) or a round "disk" form. At present, only the MDI form is practical for use in cats. Recently, the propellants used for these medications have changed. The efficacy of the medication delivered by the newer propellant has not been affected.
The most effective means of using an MDI involves coordination between inhalation and actuation of the device, something that is not reliable in most infants, small children or animals. For this reason, an alternative involves the use of a spacer device and a mask specifically designed for cats. A small, aerosol-holding chamber is attached to an MDI on one end and a face mask on the other. The spacer is approximately the size of the inner cardboard roll used with toilet paper. The MDI supplies precise doses of the aerosol drug, and the holding chamber contains the aerosol so it can be inhaled when cats inspire. The mask is designed to cover the cat's nose.
The designers of one popular spacer have shown that a holding chamber with a length of 11 cm and a diameter of >3.5 cm delivered almost all of a therapeutically "ideal" aerosol (i.e., aerosol of equivalent aerodynamic diameter <2.8 mcg) produced by an MDI, and in some cases delivery was enhanced because of evaporation of large, suspended particles.
The choice of spacer is relevant because cats have a tidal volume of between 5 ml and 10 ml inspired air per pound of body weight.
Using these spacer devices, cats will inhale the majority of drug propelled into the spacer by breathing seven to 10 times through the spacer-mask combination after actuation of the MDI.
It is important to teach the owner to observe the cat actually breathing, because cats initially may hold their breath when introduced to this form of treatment.
The procedure is not time-consuming, but it can be helpful to acclimate the cat to the mask. When administering inhalation therapy, the MDI is first shaken to open an internal valve within the canister, and then it is attached to the spacer. The mask attached to the other end of the spacer is placed snuggly on the animal's nose or muzzle, and the MDI is pressed to release the medication into the spacer.