Test: Spirometry

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Background/Purpose

Spirometry is the term given to the basic lung function tests that measure the air that is expired and inspired. There are three basic related measurements: volume, time and flow. Spirometry is objective, noninvasive, sensitive to early change and reproducible. With the availability of portable meters it can be performed almost anywhere and, with the right training, it can be performed by anybody. It is performed to detect the presence or absence of lung disease, quantify lung impairment, monitor the effects of occupational/environmental exposures and determine the effects of medications.
Spirometric measures include the following.
Forced expiratory volume in 1 s (FEV1)
Forced vital capacity (FVC), the maximum amount of air that can be exhaled when blowing out as fast as possible
Vital capacity (VC), the maximum amount of air that can be exhaled when blowing out as fast as possible
FEV1/FVC ratio
Peak expiratory flow (PEF), the maximal flow that can be exhaled when blowing out at a steady rate
Forced expiratory flow, also known as mid-expiratory flow; the rates at 25%, 50% and 75% FVC are given
Inspiratory vital capacity (IVC), the maximum amount of air that can be inhaled after a full expiration

Procedure

Ensure all pieces of equipment are clean before beginning test.
Document what medications have been taken to understand if the measurement is with or without medications which may alter results.
The patient sits in front of the machine with feet flat on the floor. Loosen tight clothes.
It is helpful to have a chair with arms, since some patients may become light headed with the test.
There are a number of different techniques for performing spirometry.
The best two measurements must fulfil the reproducibility criteria.

For FEV1 and FVC, the best two values should be within 5% or 150 mL of each other, whichever is greater. If FVC is <1.0 L, then the values should be within 100 mL.
The best FEV1 and FVC can be taken from different maneuvers.
If this is not achieved, more maneuvers are required. There is usually an upper limit of eight maneuvers, as performing forced exhalations is extremely tiring and the patient is unlikely to obtain better values after this point.
There can be problems with reproducibility: forced expiration can cause bronchoconstriction, so there must be ≥30 s between maneuvers. For some patients, particularly asthmatics, several minutes may need to be left. However, full inspiration can cause bronchodilation, so it is important to keep going until there is no further improvement.

Before performing the forced expiration, tidal (normal) breaths can be taken first, then a deep breath taken in while still using the mouthpiece, followed by a further quick, full inspiration.

Alternatively, a deep breath can be taken in then the mouth placed tightly around the mouthpiece before a full expiration is performed.

The patient can be asked to completely empty their lungs then take in a quick full inspiration, followed by a full expiration.

The latter technique can be useful in patients who may achieve a larger inspiration following expiration.

For FVC and FEV1, the patient takes a deep breath in, as large as possible, and blows out as hard and as fast as possible and keeps going until there is no air left.

PEF is obtained from the FEV1 and FVC maneuver.

For VC, the patient takes a deep breath in, as large as possible, and blows steadily for as long as possible until there is no air left. Nose clips are essential for VC as air can leak out due to the low flow.

The IVC maneuver is performed at the end of FVC/VC (depending on what type of equipment is used) by taking a deep, fast breath back in after breathing all the way out.
Encouragement makes a big difference, so don't be afraid to raise your voice to encourage the patient, particularly near the end of the maneuver. The patient needs to keep blowing until no more air comes out and the volume–time trace reaches a plateau with <50 mL being exhaled in 2 s. Some patients, particularly those with obstructive disease, may find it difficult to exhale completely on a forced maneuver. A relaxed VC may produce better results in this case.
Performed: Bilaterally

Dialog

Lung function measurement, involving the volume of inspired and expired air.

Criteria

• Normal ratios

Measurement

LOINC Code

81459-0

Scale/Grading

selection range; grade - LOINC ID
Option - Value option selection range; grade - LOINC IDNormal = ; Pass - Obstruction = ; Fail - Restriction = ; Fail -