There are many procedures involved in spirometry. OH adviser Diane Romano-Woodward covers the basics.
Spirometry is the assessment of the functioning of the lungs by measuring the flow rate and volume of air that is expelled after a deep inspiration. An introduction to the subject has been given by Gibbons (2004).
Use in occupational health
- As a baseline for health surveillance for those exposed to respiratory hazards, asbestos, dusts, fumes and gases covered by the Control of Substances Hazardous to Health Regulations.
- To assess fitness for role – for example, home office guidelines, police and firefighters.
- As ongoing health surveillance for continued exposure to respiratory hazards, irritants and sensitisers. Checking for the development of obstructive conditions where there is airway narrowing, such as asthma and chronic obstructive pulmonary disease. Checking for disease – causing restriction where the lungs are “stiff” and cannot expand to normal volumes, such as tumours, pneumoconiosis, asbestos-related disease and external allergic alveolitis.
- Records should be kept for at least 40 years:
- to assess suitability to use breathing apparatus; and
- after accidental exposures.
Standards of Care for Occupational Asthma were initially published in Thorax in March 2008, and an update of the evidence for the standards was published in the same magazine in December 2011 (Fishwick, 2011).
The British Occupational Health Research Foundation produced guidance on occupational asthma in 2004, updated in 2010, which includes a leaflet for OH practitioners.
Parameters – what is measured?
Volumes are measured in litres
- Vital Capacity (VC) – the volume of air exhaled in a normal, slow exhalation.
- Forced Vital Capacity (FVC) – the volume of air exhaled in a forced exhalation.
- FEV1 – the volume of air expelled in the first second. People with asthma or other obstructive disease may have a normal FVC, but it takes them longer to expel the air and therefore the amount expelled in the first second may be reduced.
- FEV1% (or FEV1/FVC or FER, the forced expiratory ratio) – the FEV1 compared with the FVC and expressed as a percentage.
Flow rates are measured in litres per minute
- Peak Expiratory Flow Rate (PEFR) – the maximum flow achieved during an FVC manoeuvre.
- FEF25-75 – forced mid-expiratory flow is an indicator of small airways obstruction. However, it is widely variable, even for the same individual, and should not be used for diagnosis of disease or impairment (Townsend, 2011).
- Lower Limit (LLN) of the referent range – the point at which 5% of the non-exposed asymptomatic subjects are expected to fall.
Equipment consists of the spirometer and the syringe, which should be stored and transported together so they are at the same temperature. In cold weather, they will need to be brought up to room temperature before use.
Two types of spirometers are in use: volume displacement, which are large, bellows-type static machines usually found in hospital clinics and some OH departments; and portable machines, which are flow spirometers often with a spinning turbine.
Disposable, single-use mouthpieces should be used, preferably with a one-way valve.
Barrier filters are available, although in OH settings spirometry is generally deferred if the person has a respiratory infection. However, they may be useful if the person has a known history of previous infection or is immunocompromised (Kendrick et al, 2003).
A three-litre syringe should be used, and although some machines can be programmed to use a one-litre syringe, this is not considered best practice.
- Annual calibration of spirometer and syringe by manufacturer or specialist medical equipment supplier.
- Monthly check of syringe for leaks.
- Daily checks: visually check that the patent of the tubing and flow head look normal.
- The machine should be validated by three passes of the three-litre syringe at different speeds – for example, taking 0.5 seconds, three seconds and six seconds to depress the plunger.
- If there is no calibration option on the machine, use the FVC setting.
- The response to a standard three-litre calibration syringe injection should be +3.5% or 2.90 to 3.10 litres (Town-send, 2010).
- Validation results should be kept indefinitely as they may be required in the event of audit or litigation. If the spirograms and validation slips are produced on heat-sensitive (thermal) paper, they will need to be photocopied as they fade over time. This can be done on the same sheet of paper.
- If a syringe is not available, a biological quality control check may be performed using a healthy individual to perform three technically correct breaths.
- If the temperature changes by more than 1ºC during the session, the validation should be checked again on volume displacement spirometers.
Cleaning and disinfection
- Leave at least five minutes between clients to allow settling of aerosol droplets.
- Follow the manufacturer’s instructions – these can usually be found on the website.
- Cleaning is the removal of visible particulate contamination. All parts need cleaning, including outer casing. Wipe accessible areas with a 70% alcohol wipe, but avoid using alcohol or solvents on screens. This may include cleaning with mild detergent in water and rinsing with de-ionised water on a daily basis.
- The parts of the spirometer that come into contact with subjects – for example, flow head – require cleaning and disinfecting at least monthly or every 100 clients, according to the manufacturer’s instructions.
- Disinfectants may include sodium dichloroisocyanurate (NaDCC) solution at 1,000ppm concentration of free chlorine for 15 minutes, or PeraSafe for not more than 10 minutes.
- Additional disinfection: the equipment should be disinfected prior to sending it for calibration or repair. If a client is known to be immunocompromised, he or she should be scheduled to have the lung function testing after disinfection; if the person has a past history of significant respiratory infection, the equipment should be disinfected immediately afterwards.
- If a nose clip is used, consideration will need to be given to hygiene unless the nose clip is disposable.
The technician or nurse
- Should have initial training and a refresher every five years (Townsend, 2011).
- Should be able to identify common sensor errors and technique error from the spirogram. This is outside the scope of this article, but is explained by Townsend (2011).
- Should explain the procedure and demonstrate what is expected, as well as giving verbal encouragement during the procedure (explain/demonstrate/coach). An eight-minute video produced by NHS Westminster of this procedure is available on YouTube.
- Should be able to recognise the employee’s degree of effort and cooperation.
- Should have spirograms audited by a more experienced practitioner every three months, aiming to have at least 80% of spirograms technically acceptable. This may need to be more frequent if the technician is inexperienced or is producing technically inadequate results. Choose a random selection, all of which should be invalid tests and those with abnormally low or improbably high FEV or FVC (greater than 130% of predicted).
The employee: contraindications
These are discussed and updated by Cooper (2010). This paper is worth reading as the implications are that the time periods required to defer spirometry because of health conditions and surgery can be much shorter.
However, the generally accepted contraindications and confounders are:
- recent cerebral aneurysm or concussion;
- unstable cardiovascular status/angina/recent myocardial infarction;
- coughing blood without a known reason;
- pneumothorax in the past six weeks;
- systolic blood pressure over 160mmHg (as the effort required is likely to raise it by a further 40mmHg) – blood pressure should be measured on each occasion;
- any acute illness that might affect the employee’s ability to do the test – for example, vertigo, vomiting or nausea;
- thoracic aneurysm, because of risk of rupture;
- surgery to thorax, abdomen (12 weeks) or eyes (within six weeks);
- within 30 minutes of strenuous exercise;
- within two hours of a heavy meal;
- within one hour of smoking; and
- within four hours of consuming alcohol.
The employee: variation
- For transgender individuals use genetic (birth) sex.
- For wheelchair users or those unable to stand arm span is a good approximation of height (see www.spirxpert.com/technical9.htm).
- Racial differences are caused by differences in trunk length relative to standing height, fat-free mass, chest dimensions and strength of respiratory muscles (Pellegrino, 2005). Some machines will apply an automatic correction to reduce the values affected. The employee should be asked to identify their own race or ethnic origin. Consistency is important, so use the same ethnic origin for all subsequent tests. As a rule of thumb, for Asian and African workers, the values are multiplied by 0.88. The predicted values and LLN for FEV1/FVC are not race adjusted (Townsend, 2011). However, this is a complex issue and Quanijer et al devote 48 pages to it. Some spirometers have several racial categories, and for mixed ethnic descent it is appropriate to use “other” if available.
- Pregnancy: as consistency is important due to results not being comparable with other year-on-year results, defer until the end of pregnancy.
The Health and Safety Executive (HSE) has produced simple initial and follow-up questionnaires for health surveillance for occupational asthma. However, there are concerns about many respiratory questionnaires used in terms of sensitivity and specificity, and it has been identified that further standardisation and validation is desirable (Lewis and Fishwick, 2013).
From a practical point of view, it would be useful to record:
- full name;
- date of birth;
- unique identifier – for example, national insurance or payroll number;
- checklist of contraindications;
- any respiratory symptoms;
- ethnic origin;
- height in centimetres, without shoes;
- weight in kg, if this can be entered on the spirometer – obesity may lead to lower values, and weight loss to higher valves;
- blood pressure;
- occupational history;
- smoking history;
- whether the test was conducted sitting or standing; and
- whether a nose clip is used, which is recommended (Townsend, 2011).
Preparation of environment
The ambient temperature should be between 17ºC and 40ºC.
A chair with arms and without wheels should be positioned behind the patient for standing procedures. The test should be conducted standing unless there is a history of fainting or clinical illness, in which case the sitting position should be used (Townsend, 2011).
- The flow loops should be observed as the procedure is undertaken, in order to spot errors in technique.
- There should be less than 5% variation in breaths and less than a 0.2 litre (200ml) difference in values of FVC or FEV1.
- The breath should continue for at least six seconds until the FVC plateaus on the volume-time curve.
- A valid test is one in which there are three or more acceptable curves. If this is not the case, additional breaths should be attempted, up to eight in total.
- There should be no obvious errors or technical flaws.
- The largest FVC and the largest FEV1 are reported as test results, although they may be obtained for different breaths.
- It is important to compare the results with the previous year’s and note the percentage change of FEV1, even if the spirogram would be considered normal. Healthy workers who start with above average baseline values can experience a significant loss of function because of work exposures and yet still produce apparently normal results. Comparing tests in this way is called longitudinal evaluation.
- If the loss is greater than 15% since the previous spirometry, the advice of an OH physician should be sought.
- A commonly accepted criterion for referral or advice is if the FEV1 or FVC is less than 80% or the FEV1% is less than 75%. However, if the FEV1% is low but the FEV1 is normal, it is usually because of a high FVC. This is considered a normal physiological variant and referral is not required.
These criteria do lead to an underdiagnosing of altered airway functioning in young people (false negative) and an over-reporting in the older population (false positive) and are being challenged. Using the fifth percentile LLN to define abnormality for the major respiratory measurements avoids these problems (Townsend, 2011).
1. Collect information in a procedure manual to include:
- details of equipment type;
- spirometer configuration;
- manufacturer’s guidelines;
- calibration log;
- service and repair record, including log of any technical problems found and rectified by OH staff;
- personnel training; and
- standard operating procedures.
2. Ensure that you are able to identify the following errors on test results and curve shapes (Townsend, 2011):
- sensor error-zero flow errors caused by blockage or contamination of a flow-type spirometers sensor;
- hesitation/slow start;
- glottal stop;
- extra breaths;
- submaximal inspiration;
- no blast/weak push; and
- early termination before five seconds (if no plateau).
3. Agree referral criteria with the OH physician supervising the health surveillance for paper screening of spirograms and face-to-face consultations. This may include what variation or percentage reduction is acceptable between spirograms separated in time – for example, annual tests, even if they are “normal”.
Diane Romano-Woodward is an OH adviser at Sunny Blue Sky
Providers of spirometry training
- Association of Respiratory Technology and Physiology
- Royal Brompton Hospital
- Imperial College
- Lung Function Testing in the Workplace: Introductory Level
- Lung Function Testing in the Workplace: Intermediate Level
- Occupational Lung Disease: Keeping Up to Date
Cooper B (2010). An update on contraindications for lung function testing.
Cullinan P (2011). Evidence based guidance for the assessment of new employees with asthma. A report to the British Occupational Health Research Foundation, December 2011.
Fishwick D, Barber C, Bradshaw LM, Ayres J, Barraclough R, Burge S et al (2011). “Standards of care for occupational asthma: an update”. Thorax 2012; vol.67, issue 3, pp.278-280.
Gibbons D (2004). Practice – a comprehensive guide to the accurate performance of spirometry tests. Nursing Times, published online 1 July 2004.
Kendrick AH, Johns DP, Leeming JP (2003). “Infection control of lung function equipment: a practical approach”. Respiratory Medicine; vol.97, issue 11, pp.1,163-1,179.
Lewis L, Fishwick D (2013). Health Surveillance for Occupational Respiratory Disease. Occupational and Environmental Medicine; vol.63, pp.322-334
MHRA Medicines and Healthcare Products Regulatory Agency Managing Medical Devices 2006.
Quanijer P, Stanojevic S, Cole T, Xavier B, Hall G, Culver B et al (2012). ERS Global Lung Function Initiative (2012). Multi-ethnic reference values for spirometry for the 3-95 year age range:the global lung function 2012 equations. ERJ Express.
Pellegrino R, Viegi G, Brusasco V, Crapo R et al (2005). “Interpretative strategies for lung function tests series ats/ers task force: standardisation of lung function testing”. European Respiratory Journal; vol.26, pp.948-968.
Romano-Woodward D (2010). “The dust settles – guidance on occupational asthma”. Occupational Health; vol.62, no.10, pp.16-18.
Townsend PH et al (2011). “Spirometry in the Occupational Health setting”. 2011 Update from the American College of Occupational and Environmental Medicine. Journal of Occupational and Environmental Medicine; vol.53, issue 5, pp.569-584.