How do you determine spirometry in a patient with a history of respiratory disease, considering age, height, sex, ethnicity, and medication use?

How to Determine Spirometry

Spirometry should be performed with the patient seated upright in a chair with armrests, using a calibrated spirometer that produces hard copy tracings, with at least three acceptable maneuvers obtained after withholding short-acting bronchodilators for 4 hours and long-acting bronchodilators for 12 hours. 1, 2, 3

Patient Preparation and Positioning

Pre-Test Medication Withholding

• Withhold short-acting β-agonists (albuterol) for 4 hours before testing to assess true baseline lung function 3
• Withhold long-acting β-agonists (salmeterol, formoterol) for 12 hours prior to testing 3
• Withhold anticholinergic agents (ipratropium) for 4 hours before the procedure 3
• Withhold oral aminophylline or slow-release β-agonists for 12 hours 3
• Avoid smoking for 1 hour prior to and throughout testing 3

Patient Positioning

• Seat the patient upright in a chair with armrests and without wheels for safety 2
• Maintain upright posture with head slightly elevated throughout the entire procedure 2
• Apply a nose clip or manually occlude the nares during all maneuvers 2

Equipment Requirements and Calibration

Spirometer Selection

• Choose a spirometer that produces hard copy tracings large enough to verify computer-reported values from graphs 1
• Ensure volume/time plot is displayed (mandatory), with flow-volume plot optional 1
• Verify the device allows superimposition of traces to compare different attempts 1

Calibration Standards

• Calibrate volumetric devices weekly using a 3-liter syringe 1, 2
• Calibrate flow-based devices daily using a 3-liter syringe 1, 2
• Maintain volume accuracy within ±3.5% of reading or ±65 mL (whichever is greater) 2

Performing the Maneuver

Three Phases of FVC Maneuver

1. Maximal inspiration to total lung capacity 2
2. "Blast" exhalation with immediate forceful effort 2
3. Continued complete exhalation until volume plateau is reached 2

Start-of-Test Criteria

• Extrapolated volume (EV) must be <5% of FVC or <0.150 L (whichever is greater) to ensure accurate time zero 1
• Peak expiratory flow (PEF) should occur with a sharp rise close to the point of maximal inflation 1
• Terminate early if the patient shows obvious hesitant start to avoid unnecessary prolonged effort 1

End-of-Test Criteria

• Continue exhalation until volume plateau is reached with no change in volume (<0.025 L) for ≥1 second 1
• Minimum exhalation time: ≥3 seconds for children <10 years 1
• Minimum exhalation time: ≥6 seconds for subjects ≥10 years 1
• Allow up to 15 seconds for patients with severe COPD to reach volume plateau, as abbreviated efforts underestimate FVC 1
• Stop immediately if patient experiences discomfort or shows signs of approaching syncope 1, 2

Number of Maneuvers and Acceptability

Repeatability Requirements

• Perform a minimum of three acceptable maneuvers, with no more than eight usually required 2, 4
• Obtain at least two readings of FEV₁ within 100 mL or 5% of each other 1
• For clinical trials, use stricter criteria of ≤100 mL for within-test reproducibility 1

Unacceptable Maneuvers (Exclude from Analysis)

• Cough during the first second that interferes with accurate measurement 1
• Valsalva maneuver (glottis closure) or hesitation that causes cessation of airflow 1
• Leak at the mouth during the maneuver 1
• Obstruction of the mouthpiece (e.g., by tongue placement) 1
• Volume-time curves that are not smooth, convex upwards, or show irregularities suggesting variable effort or coughing 1

Interpretation and Reference Values

Reference Equations to Use

• Apply GLI-2012 (Global Lung Function Initiative) reference equations for whites, African Americans, North East Asians, and South East Asians, ages 3-95 years 1
• GLI-2012 white reference values are applicable in the United States, Europe, Hispanic regions, and for Hispanic Americans 1
• Use lower limit of normal (LLN) set at the 5th percentile (z-score of -1.645) to distinguish health from suspected disease 1

Key Parameters to Report

• Report the best FEV₁ and best FVC values from acceptable maneuvers 1
• Calculate FEV₁/FVC ratio to diagnose airflow obstruction (ratio <70% indicates obstruction) 1, 5
• Adjust for age, height, sex, and ethnicity when comparing to predicted values 1, 5

Adjusting for Patient Characteristics

• Age: Reference equations account for age-related decline in lung function 1
• Height: Taller individuals have larger predicted values; in long-term pediatric studies (>12 months), adjust for height at each visit 1
• Sex: Males typically have higher predicted values than females 1
• Ethnicity: Use ethnicity-specific GLI-2012 equations (white, African American, North East Asian, South East Asian) 1

Safety Considerations

Monitoring for Syncope

• Supine positioning increases syncope risk, especially in older subjects and those with airflow limitation 2
• Stop the test immediately if dizziness occurs to prevent syncope 2
• Consider performing vital capacity (VC) maneuver instead of FVC in patients at higher risk of syncope 2
• Monitor closely for signs of distress, as altered hemodynamics in supine position increase syncope risk 2

Common Pitfalls to Avoid

• Do not use electronic spirometers without hard copy tracings, as they may lead to underestimation of FEV₁ and FVC due to inability to verify test reliability 1
• Do not report results without verifying at least three technically satisfactory readings that meet acceptability and repeatability criteria 1
• Do not use percent predicted values as outcome variables (except in long-term pediatric studies); use absolute values adjusted for age, sex, and height 1
• Do not rely on peak expiratory flow (PEF) alone, as it poorly correlates with FEV₁ in COPD and may underestimate airflow obstruction 1
• Do not continue exhalation beyond 15 seconds in most cases, as this rarely changes clinical decisions and may cause syncope or undue fatigue 1