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Respiratory therapy is a vital component of health care. For
any patient initial medical care begins with assessment of the ABCs: Airway, Breathing,
and Circulation. Respiratory therapy
includes key components of airway and breathing support. The objective
is the care of all types of patients with cardiopulmonary diseases.
Functions of the respiratory therapist include emergency care, airway
management, ventilatory support, oxygen therapy, humidity and aerosol
therapies, chest physiotherapy, physiologic monitoring, and pulmonary diagnostics.
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PFTs are useful in the diagnosis of a variety of pulmonary disorders.
Common PFTs include spirometry, lung volume determinations, and
diffusion capacity. Important measurements include FVC and FEV1.
Spirometry results indicate the presence of obstructive airway diseases
such as asthma and emphysema when the FEV1/FVC
ratio is < 0.70. They indicate the presence of restrictive lung
diseases such as sarcoidosis and ankylosing spondylitis when the
FVC/FEV1 ratio > 80%.
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Spirometry can be an important part of a preoperative evaluation.
Obtain spirograms before and after administration of bronchodilators
if they are not contraindicated (ie, history of intolerance). Bronchodilator
responsiveness helps in predicting the response to treatment and
in identifying asthma. Asthmatic patients typically have at least
15% improvement in FEV1 after bronchodilator therapy.
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Order lung volumes, commonly determined by helium dilution, to
definitively diagnose restrictive lung disease. This test is usually
indicated when TLC < 80% of predicted normal value.
Diffusion capacity is important in the diagnosis of interstitial
lung disease and pulmonary vascular disease, in which it is reduced.
Diffusion capacity is frequently monitored to determine response to
therapy for interstitial diseases.
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Obstructive pulmonary diseases include
asthma, chronic bronchitis, emphysema, and bronchiectasis. Restrictive pulmonary diseases include
interstitial pulmonary disease, diseases of the chest wall, and
neuromuscular disorders. Interstitial disease can be caused by inflammatory
conditions (usual interstitial pneumonitis [UIP]),
inhalation of organic dust (hypersensitivity pneumonitis), inhalation
of inorganic dust (asbestosis), and systemic disorders with lung
involvement (sarcoidosis).
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Normal PFT values vary with age, sex, race, and body size. Normal
values for a given patient are established from studies of healthy
populations and are provided along with the results. ABG should be included in all PFTs.
Typical volumes and capacities are illustrated in Figure
18–1.
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- Tidal Volume (TV). Volume
of air moved during a normal breath on quiet respiration
- Forced Vital Capacity (FVC). Maximum
volume of air that can be forcibly expired after full inspiration
- Functional Residual Capacity (FRC). Volume
of air in the lungs after a normal tidal expiration (FRC = reserve
volume + expiratory reserve volume)
- Total Lung Capacity (TLC). Volume
of air in the lungs after maximal inspiration
- Forced Expired Volume in 1 Second
(FEV1). Measured after
maximum inspiration, the volume of air that can be expelled in 1
s
- Vital Capacity (VC). Maximum
volume of air that can be exhaled from the lungs after a maximal
inspiration
- Residual Volume (RV). The volume
of air remaining in the lungs at the end of a maximal exhalation
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Table 18–1 shows the differential
diagnosis of various PFT patterns. When interpreting PFTs, remember
that some patients ...