Page 332 - Clinical Small Animal Internal Medicine

300 Section 4 Respiratory Disease

Identifying the allergens responsible for inciting the Albuterol sulfate is a beta‐2‐adrenergic agonist that
VetBooks.ir asthmatic response in individual cats is a critical step in may be administered in inhalant form to cats presenting
with severe, acute dyspnea. A metered dose inhaler is
devising targeted therapies. Methods have been devel-
oped to detect IgE that is specific for the allergens used
attached to a facemask (Aerokat® Feline Aerosol
in sensitization in the serum of cats with experimentally used to deliver the medication into a chamber device
induced asthma. Moreover, intradermal skin testing, a Chamber, Trudell Medical International). This appara-
practice most often used in the diagnosis of atopic tus facilitates inhalation of the aerosolized particles into
dermatitis, has been shown to be a sensitive means of the lower airways. An initial dose of one 90 μg puff can
detecting aeroallergen sensitization in experimental be administered to dyspneic patients that will tolerate
models of asthma. Other minimally invasive immunodi- having the facemask held over the nose and mouth for
agnostic methods that have been investigated in asth- the 7–10 seconds necessary for the complete dose to be
matic patients include the use of flow cytometry to inhaled. This dose may be repeated every 30 minutes for
detect proliferation of allergen‐specific T lymphocytes in up to four hours. Albuterol can also be dispensed for
the peripheral blood. at‐home administration as a “rescue inhaler” for man-
agement of acute exacerbations in established asthmat-
ics until veterinary care can be provided. However,
Treatment chronic use of racemic albuterol should be avoided as
the S‐enantiomer in this mixture has been shown to
Supplemental oxygen, stress reduction, and bron- cause airway inflammation in healthy and experimen-
chodilation are the tenets of therapy for the asthmatic tally asthmatic cats.
cat in acute crisis. For the patient presenting with Status asthmaticus is defined in human medicine as
dyspnea and cyanosis, supplemental oxygen should be severe, acute asthma that is refractory to repeated doses
provided immediately at a FiO 2 of 40%. This can be of beta‐agonists. Severely dyspneic feline asthmatics that
effectively accomplished by placing the patient in an do not respond to bronchodilators and supplemental
oxygen cage, which also minimizes restraint and han- oxygen may stabilize only after initiating antiinflamma-
dling that can exacerbate dyspnea, with fatal outcomes tory therapy with a rapidly acting glucocorticoid such as
in some instances. dexamethasone sodium phosphate. An initial dose of
Beta‐2‐adrenergic agonists such as terbutaline are 0.25–2 mg/kg can be administered IM or IV to quickly
most commonly used to induce bronchodilation in an reduce airway inflammation if necessary.
acute setting. Bronchodilation results from airway Lifelong glucocorticoid therapy is the key to chronic
smooth muscle relaxation triggered by stimulation of management of feline asthma. Because the aeroallergen
beta‐2‐adrenergic receptors. Activation of these recep- that provokes the asthmatic response usually cannot be
tors triggers adenylyl cyclase to increase production of identified or completely removed, avoidance of the
cAMP, which sequesters intracellular calcium, thereby offending allergen is often impossible in feline patients.
reducing smooth muscle contraction. Other potentially Thus, it is postulated that lower airway inflammation is
beneficial effects of these agents include inhibition of continually present in asthmatic cats, even in the absence
mast cell mediator release and airway microvascular of clinical signs. Lower airway inflammation has been
leakage, increased mucociliary clearance, decreased shown to persist in feline asthmatics treated with high‐
neutrophil activation and endothelial adhesion, and dose glucocorticoid therapy despite resolution of clinical
induction of neutrophil apoptosis. Adverse effects asso- signs. To minimize the permanent airway remodeling
ciated with beta‐2‐adrenergic agonist therapy include that ensues from long‐standing inflammation, continu-
tachycardia, CNS stimulation, hypokalemia, and trem- ous antiinflammatory therapy is necessary.
ors. For this reason, these agents should be used with Glucocorticoids are the most effective antiinflamma-
caution in patients with co‐morbid cardiac disease, tory agents used in the management of feline asthma.
hypertension, hyperthyroidism, seizure disorders, and They exert their antiinflammatory effects by binding to a
diabetes mellitus. Beta‐2‐adrenergic agonists can inter- cytosolic receptor, then translocating to the nucleus
act with tricyclic antidepressants such as amitriptyline where the glucocorticoid–receptor complex binds to a
and clomipramine and should be used with caution in glucocorticoid response element on the genes that regu-
patients receiving these medications. Terbutaline sul- late production of inflammatory cytokines such as IL‐3
fate can be administered IM or SC at an initial dose and IL‐5. Glucocorticoids also increase vasoconstriction
of 0.1 mg/kg to induce bronchodilation in an acute to reduce airway edema; decrease airway hyperrespon-
setting. Decreased respiratory rate is expected within siveness over time; decrease mucus secretion; inhibit
15–30 minutes of dosing, and repeated doses can be macrophages, T cells, eosinophils, and mast cells;
administered as needed. increase the synthesis of secretory leukocyte protease