23. Pulmonary Function Testing

and CHARLENE M. MYERS

The authors would like to acknowledge David A. Miller for his contributions that remain unchanged from the first edition.

I. Purpose of a pulmonary function test (PFT)

A. To determine the existence of a ventilatory defect that may then be used to do the following:

1. Assign a potential diagnosis to explain a patient’s symptoms.

2. Differentiate between obstruction of airways and decreased pulmonary parenchymal compliance as the source of a patient’s symptoms.

3. Evaluate the response to treatment of a pulmonary disease process

B. Indications for a PFT

1. Evaluate unexplained dyspnea and cough.

2. Assess severity of pulmonary pathology.

3. Determine potential reversibility of airway obstruction

C. Limitations of the PFT

1. The patient must be able to cooperate with the testing; inadequate cooperation negates the value of the testing.

2. The patient should be relatively stable with respect to symptoms. Temporary worsening of symptoms may invalidate the severity of dysfunction assessed.

II. Types of PFT

A. Spirometry continues to be recommended for the objective measurement of pulmonary function and for the diagnosis and management of respiratory dysfunction.

1. Determines forced vital capacity and forced expiratory flow rates

a. Forced expiratory volume in 1 second (FEV₁) is considered the gold standard by which obstructive airway disease is measured.

b. Values are compared with predicted values derived from population-based reference groups.

c. Decreased FEV₁ (less than 70% of normal) indicates the presence of air flow obstruction or an obstructive disorder.

2. If expiratory air flow obstruction is defined, the response to an aerosolized bronchodilator should be measured.

a. An increase of 15% to 20% or greater is often accepted as a reason to use a bronchodilator.

b. However, a smaller improvement in flow rate in the presence of more severe obstruction is a reason to consider using a bronchodilator.

3. Graphic display of exhalation (flow volume loops) provides a comprehensive view of respiratory mechanics, allows identification of subtle changes, and aids in differentiating between obstructive and restrictive disease.

4. Results correlate with morbidity and life expectancy.

5. Safe, inexpensive, and fast

6. Spirometry, however, is effort dependent, and some patients have difficulty performing the process because of advanced age or acute illness.

B. Spirometry with bronchodilator challenge (evaluation for bronchospasm)

1. Determines the vital capacity and expiratory flow rates before and after aerosolized bronchodilator challenge

2. Degree of responsiveness may be useful in determining the need for bronchodilator therapy

C. Body plethysmography

1. Useful in determining all lung volumes, including the following:

a. Vital capacity (measured during spirometry)

b. Residual volume in the chest after expiration

c. Total lung capacity

2. More completely differentiates between a restrictive ventilatory defect (lowered lung volumes) and an obstructive ventilatory defect (increased total lung volume and residual volume)

a. Total lung capacity (TLC) is decreased with restrictive disorders.

b. TLC is normal or increased with obstructive disorders.

c. Interpret cautiously in patients with neuromuscular weakness because this can sometimes decrease TLC and may prevent differentiation between restrictive and obstructive disorders.

D. Measurement of exhaled nitrous oxide (eNO)

1. Noninvasive marker of airway inflammation

a. Appears to reflect lower airway inflammation—a hallmark of the asthma disease process

b. Useful in recognizing inflammation in symptom-free asthmatic patients who have normal lung function

c. Helps with titration of inhaled steroid therapy in that inhaled steroids quickly reduce eNO levels, indicating a reduction in airway inflammation

d. Not routinely used as yet, but shows great promise in clinical studies

E. Diffusing capacity of the lung for CO (DLCO) (single-breath technique)

1. Uses carbon monoxide (CO) as a substitute for O₂ to assess the gas transfer function of the lungs

a. Decreased DLCO indicates disorders of pulmonary parenchyma, vascular problems, or decreases in alveolar function (such as occur with lung resection or emphysema).

b. Increased DLCO may indicate asthma, obesity, polycythemia, or cardiac left-to-right shunting.

2. Modified techniques to measure DLCO must be used for patients with end-stage heart disease and after heart transplant.

F. Maximal respiratory pressures (MRP)

1. Helps in diagnosis of neuromuscular causes of respiratory dysfunction

a. Decreased inspiratory AND expiratory pressures indicate generalized neuromuscular diseases such as amyotropic lateral sclerosis.

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Tags: Practice Guidelines for Acute Care Nurse Practitioners

Mar 3, 2017 | Posted by admin in NURSING | Comments Off

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