576
U N I T 6
Respiratory Function
diagnosis of asthma, they can be used in clinics and phy-
sicians’ offices and by persons in their home to provide
frequent measures of flow rates. Day–night (circadian)
variations in asthma symptoms and PEF variability can
be used to indicate the severity of bronchial hyperre-
sponsiveness. The person’s best performance is estab-
lished from readings taken over several weeks. This
often is referred to as the individual’s
personal best
and
is used as a reference to indicate changes in respiratory
function. A PEF below 40% of the predicted or personal
best during an acute asthmatic attack indicates a severe
exacerbation and the need for immediate intervention,
and a PEF below 25% of the predicted or personal best
indicates a life-threatening attack.
19
Successful management of bronchial asthma requires
control of factors contributing to asthma severity and
pharmacologic treatment. Control measures are aimed
at prevention of exposure to allergens and irritants.
They include education of the person and family regard-
ing known triggers; therefore, a careful history is needed
to identify all contributory factors. Annual influenza
vaccination is recommended for persons with persistent
asthma.
A program of desensitization may be undertaken in
persons with persistent asthma who react to allergens,
such as house dust mites, that cannot be avoided. This
involves the injection of selected antigens (based on skin
tests) to stimulate the production of IgG antibodies that
block the IgE response. A course of allergen immuno-
therapy is typically of 3 to 5 years’ duration.
19
Traditionally, drugs used to treat asthma were cat-
egorized according to their predominant mechanism of
action—relaxation of bronchial smooth muscle (bron-
chodilator) and suppression of airway inflammation
(anti-inflammatory drugs). A more recent classification
divides asthma medications into two general categories
according to their roles in the overall management of
asthma symptoms (quick-relief or long-term mainte-
nance medications).
19
Quick-relief Medications.
The
quick-relief medications
include the short-acting
β
2
-agonists, anticholinergic
agents, and systemic corticosteroids.
19,21,31
The short-
acting
β
2
-agonists relax bronchial smooth muscle and
provide prompt relief of symptoms, usually within
30 minutes. They are administered by inhalation (i.e.,
metered-dose inhaler [MDI] or nebulizer).
The anticholinergic agents block cholinergic recep-
tors and reduce intrinsic vagal tone that causes broncho-
constriction. These medications, which are administered
by inhalation, produce bronchodilation by direct action
on the large airways but do not change the composition
or viscosity of the bronchial mucus. It is thought that
they may provide some additive benefit for treatment of
asthma exacerbations when administered with inhaled
β
2
-agonists.
A short course of systemic corticosteroids, admin-
istered orally or parenterally, may be used for treating
the inflammatory reaction associated with the late-phase
response. Although their onset of action is slow (>4 hours),
systemic corticosteroids may be used in the treatment of
moderate to severe exacerbations because of their action
in preventing the progression of the exacerbation, speed-
ing recovery, and preventing early relapses.
Long-term Medications.
The
long-term medications
are taken on a daily basis to achieve and maintain con-
trol of persistent asthma symptoms. They include inhaled
corticosteroids, long-acting bronchodilators, cromolyn
and nedocromil, leukotriene receptor antagonists, and
theophylline.
19,21,31
The corticosteroids are considered
the most effective anti-inflammatory agents for use in
TABLE 23-1
Classification of Asthma Severity
Asthma
Severity
Symptoms, Interference with
Normal Activities, and Frequency of
Short-Acting
β
2
-Agonist Use
Nighttime
Awakenings
Lung Function
Mild
intermittent
Symptoms
≤
2 days a week
No interference with normal activity
Short-acting
β
2
-agonist use <2 days a week
<2 times a month Normal FEV
1.0
between exacerbations
FEV
1.0
>80% predicted
FEV
1.0
/FVC normal
Mild persistent
Symptoms 2 days a week but not daily
Minor limitation in normal activity
Short-acting
β
2
-agonist use
≥
2 days a
week but not daily
3–4 times a month FEV
1.0
>80% predicted
FEV
1.0
/FVC normal
Moderate
persistent
Symptoms daily
Some limitation in normal activity
Short-acting
β
2
-agonist daily
>1 time a week
but not nightly
FEV
1.0
>60% normal but <80%
predicted
FEV
1.0
/FVC reduced 5%
Severe
persistent
Symptoms throughout the day
Extreme limitation in normal activity
Short-acting
β
2
-agonist several times a day
Often 7 times a
week
FEV
1.0
<60% normal
FEV
1.0
/FVC reduced >5%
FEV
1.0
, forced expiratory volume in 1 second; FVC, forced vital capacity.
Adapted from National Lung, Heart, and Blood Institute National Asthma Education and Prevention
Program. Expert Panel Report 3: Guidelines for Diagnosis and Management of Asthma. Bethesda, MD:
National Institutes of Health; 2007.
