What are the guidelines for performing supine spirometry (forced expiratory volume) in patients?

Guidelines for Performing Supine Spirometry

Spirometry should be performed with the patient in a sitting position with head slightly elevated, as this is the standard recommended position for optimal results according to the European Respiratory Society guidelines. 1

Standard Positioning for Spirometry

• The European Respiratory Society recommends performing spirometry with the patient seated in a chair with armrests and without wheels for safety reasons 1
• Patients should maintain an upright posture with head slightly elevated throughout the procedure 1, 2
• Changing from sitting to supine position results in statistically significant changes in respiratory patterns and spirometry values, even in healthy individuals 3

When Supine Spirometry May Be Necessary

• While not the standard position, supine spirometry may be required in specific clinical scenarios where patients cannot sit upright 3
• In healthy individuals, supine positioning leads to decreased values in FVC (95% of predicted vs 102% when sitting), FEV1 (96% of predicted vs 104% when sitting), and MVV (102% of predicted vs 115% when sitting) 3
• These positional changes should be considered when interpreting results from supine spirometry 3

Procedure for Supine Spirometry

• Patient should lie flat on their back on an examination table 3
• A nose clip or manual occlusion of the nares is still recommended in the supine position 1, 2
• The three phases of the FVC maneuver remain the same as in sitting position: maximal inspiration, "blast" exhalation, and continued complete exhalation 1, 4
• Monitor the patient closely for signs of distress, as the risk of syncope may be higher in the supine position due to altered hemodynamics 1

Quality Control Considerations for Supine Spirometry

• The same acceptability criteria apply to supine spirometry as to standard sitting spirometry 2:
  • Volume extrapolated must be <5% of FVC or 0.150 L (whichever is greater)
  • The curve must show rapid ascent with PEF occurring near maximum inflation
  • End of test criteria must be met (no volume change >0.025 L for at least 1 second)
• A minimum of three acceptable maneuvers should be performed, with no more than eight usually required 1, 2
• Reproducibility is achieved when the difference between the two largest FVC values is ≤0.150 L and the difference between the two largest FEV1 values is ≤0.150 L 2

Special Considerations and Pitfalls

• Supine positioning may increase the risk of syncope, especially in older subjects and those with airflow limitation 1
• If dizziness occurs during the maneuver, stop the test immediately to prevent syncope 1
• Consider performing a vital capacity (VC) maneuver instead of FVC in patients at higher risk of syncope 1
• Interpretation of results must account for the expected reduction in values when compared to sitting position (approximately 7-8% lower for FVC and FEV1) 3
• Document the patient position during testing in the medical record to ensure proper interpretation of results 2

Technical Requirements

• The same equipment calibration standards apply regardless of patient position 1
• Volume accuracy must be within ±3.5% of reading or ±65 mL (whichever is greater) 1
• For flow-measuring devices, calibration checks must be performed daily using a 3-L syringe 1