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Spirometry requires maximal effort from the patient and it takes time to perform quality spirometry. It is essential the procedure is carefully and clearly explained and to actively coax and motivate the patient to perform maximally. The volume and flow parameters measured are defined in terms of maximal effort and maximal exhaled volume. The performance of spirometry while seated upright in a chair is preferable to standing as this is the most stable position should the patient experience dizziness during the test. The seated position is also preferable for patients with urinary incontinence who may otherwise limit the expiratory effort.
The key steps are to urge the patient to:
- Breathe in fully (the lungs must be absolutely full).
- Seal the lips around the mouthpiece and immediately….
- Blast the air out as fast and as far as possible until the lungs are completely empty.
- Repeat the test until three acceptable and reproducible results are obtained (up to a maximum of 8 efforts)
- The highest FEV1 and FVC should be reported, even if they come from separate blows.
While it is not mandatory to use nose clips to prevent loss of measured volume through the nose, their use is sometimes of benefit.
Acceptable Results and Real-time Display
Acceptable results are those that were initiated at full lung inflation, and with maximum expiratory effort (eg no hesitation at the start and no pauses throughout the blow) until no more air can be expired. The results are reproducible if there is less than 200ml variation in FEV1 and FVC between the two best blows.
A spirometer that allows you to see a graph of the flow-volume curve in real-time and provides alert messages about test quality makes it much easier to determine the acceptability of each blow. It is preferable to have both flow-volume and volume-time graphic output so that the acceptability of the results can be easily judged.
Common causes of unacceptable spirometry are listed below.
Common Causes of Poor Quality Spirometry
- Sub-maximal effort (eg due to poor coaching, full bladder).
- Failure to fully inflate the lungs prior to performing the forced expiration.
- Incomplete expiration.
- Hesitation at the start of the expiration.
- Leaks (eg. between the lips and mouthpiece).
- Poorly calibrated / maintained spirometer.
- Untrained (or poorly) trained operator.
- Inability to comprehend the instructions.
- Cough.
- Glottic closure.
- Obstruction of the mouthpiece by the tongue or teeth.
- Vocalisation during the forced manoeuvre.
- Poor posture (eg. leaning forward or slouching).
Examples of poorly performed spirometry are shown in Figure 1.
Figure 1
Examples of acceptable and poorly performed spirometry for a healthy subject.
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Contraindications
Spirometry is a very safe procedure. However, it is physically demanding as it requires maximal patient effort and it involves the generation of high airway and intrathoracic pressures. It is advisable that spirometry be delayed/ abandoned for:
- Recent eye surgery.
- Recent thoracic and abdominal surgery.
- Aneurysms (e.g. cerebral, abdominal).
- Unstable cardiac function.
- Haemoptysis of unknown cause (e.g. ? TB).
- Pneumothorax.
- Chest and abdominal pain.
- Nausea and diarrhoea.
- Inability to comprehend the instructions
Additionally children below the age of 7 years may have difficulty performing the test consistently.
Content Updated February 2005
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