Key learning points
- Spirometry is recommended in both asthma and chronic obstructive pulmonary disease (COPD) guidelines
- Variability in the performance and understanding of spirometry interpretation has resulted in an estimated 50% of people having an incorrect diagnosis
- Spirometry consists of two measurements, the relaxed vital capacity (VC) and the forced vital capacity (FVC)
- There should be three attempts at all blows as a check of repeatability/reproducibility
The use of spirometry as an objective measurement in the diagnosis of respiratory disease is widely acknowledged. It is recommended in both asthma and chronic obstructive pulmonary disease (COPD) guidelines, as well as those specific to spirometry.1-4
It is a relatively straightforward test to undertake and is essentially a practical skill. It has been available and performed in primary care for several years now, but with varying degrees of expertise and understanding.5
The variability in performance and poor understanding of spirometry interpretation has resulted in an estimated 50% of people receiving an incorrect diagnosis.6 Consequently, people are prevented from receiving appropriate treatment for their condition, or conversely receive medication they do not need.
Key areas: Preparing the equipment
Spirometry must always be quality assured and performed to an approved standard.2,4
In general, all equipment should be:
- Verified with a 3 litre syringe ideally before each session but at least daily
- Cleaned regularly according to manufacturer’s instructions
- Operated with a one-way single-patient-use mouthpiece
Preparing the patients
Patients should be well enough to undertake the test, and relative contraindications should be considered and recorded.
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|Due to increases in intracranial/intraocular pressure|
|Due to increases in sinus and middle ear pressures|
|Due to increases in intrathoracic and intraabdominal pressure|
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Patient comfort should also be considered and patients should be asked in preparation for the test to avoid:2,4
- Eating a substantial meal before the test
- Drinking alcohol 8 hours before the test
- Smoking for at least 24 hours before the test
- Vigorous exercise an hour before the test
- Wearing restrictive clothing
Performing the test
Spirometry consists of two measurements, the first is the relaxed vital capacity (VC), and the second is the forced vital capacity (FVC).
Relaxed vital capacity or VC
For this test, the patient must wear a nose clip or hold their nose. They are encouraged to take a maximum breath in, and then slowly and steadily exhale until all of the air is expelled and they cannot blow any more.
During the test, the mouthpiece should be completely within the mouth enclosed tightly by the teeth and not blocked by the tongue. Disposable, one-way filter mouthpieces should be used.
This should be repeated at least two more times and the values recorded manually to enable a check of repeatability/reproducibility. Guidelines state that three good blows should be performed, and the best two blows should be within 100 ml of each other.4
Forced vital capacity or FVC
The forced expiratory volume (FEV1) is taken from this test. FEV1 is the amount of air that is blown out in the first second of the FVC. A nose clip is not required for this test. Patients are encouraged to take a maximum breath in, and then exhale hard and fast until all of the air is expelled and they cannot blow any more.
As with the VC, the mouthpiece should be completely within the mouth enclosed tightly by the teeth and not blocked by the tongue. Disposable, one-way filter mouthpieces should be used.
This test should be repeated at least two more times and the values recorded manually to enable a check of repeatability/reproducibility. Guidelines state that three good blows should be performed and the best two blows should be within 100 ml of each other.4 This applies to both the FEV1 and the FVC values. For example:
- FVC | 4.26 | 4.28 | 4.32
- FEV1 | 3.99 | 3.97 | 3.99
The best two FVC values are within 40 ml of each other. All three are within 100 ml of each other. The best two FEV1 are the same, but are also only 20 ml different from the third blow. These results suggest this is a highly reproducible/repeatable test.
Finally, before the test can be interpreted, all readings and graphs need to be checked to see if they are also technically acceptable.
Some common technical errors in spirometry4
Further information about accredited spirometry training can be found at www.educationforhealth.org/news/spirometry-course-update or www.artp.org.uk/spirometry-overview
Chris Loveridge is a primary care respiratory nurse and director at Inspirometry Training and Consultancy Limited
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