Standard Operating Procedure: Diagnostic Spirometry

This Standard Operating Procedure (SOP) outlines the requirements for performing high-quality, reproducible diagnostic spirometry in accordance with American Thoracic Society (ATS) and European Respiratory Society (ERS) standards. Accurate spirometry is essential for the diagnosis and management of obstructive and restrictive lung diseases. The objective of this procedure is to ensure patient safety, minimize technical variability, and obtain valid measurements of Forced Vital Capacity (FVC), Forced Expiratory Volume in 1 second (FEV1), and the FEV1/FVC ratio.

Phase 1: Preparation and Patient Screening

• Equipment Calibration: Perform a volume verification using a 3-liter calibration syringe daily (or per manufacturer specifications). Record results in the logbook.
• Environment Check: Ensure the room is well-ventilated, ergonomic, and provides sufficient privacy for the patient.
• Contraindication Screening: Screen the patient for recent abdominal/thoracic surgery, eye surgery (within 6 weeks), recent myocardial infarction, unstable angina, or thoracic/abdominal aneurysms.
• Medication Review: Confirm whether the patient has withheld short-acting bronchodilators for at least 6 hours (or per physician order).
• Patient Instructions: Explain the procedure clearly. Demonstrate the maneuver using a new mouthpiece, emphasizing a "full blast" start and a "long, continuous" finish.

Phase 2: Execution of the Maneuver

• Positioning: Ensure the patient is seated upright with feet flat on the floor. Maintain an erect posture; do not allow the patient to lean forward excessively during exhalation.
• Nose Clip: Apply a nose clip to ensure no air leakage occurs through the nasal passages.
• The Breath: Instruct the patient to take the deepest breath possible (Total Lung Capacity) before sealing their lips tightly around the mouthpiece.
• The Blast: The patient must blast the air out with maximal force immediately upon sealing the lips, with no hesitation.
• The Sustain: Encourage the patient to continue exhaling until the lungs are completely empty (at least 6 seconds, or until no more air can be expelled).
• Repetition: Perform at least three acceptable maneuvers. A maximum of eight attempts is allowed to achieve reproducibility.

Phase 3: Quality Control and Acceptance Criteria

• Start of Test (Back-extrapolated volume): Ensure the back-extrapolated volume is <5% of FVC or 0.150 L, whichever is greater.
• End of Test: Confirm there is a plateau in the volume-time curve (no change in volume for >1 second) or the patient has reached a forced expiratory time of ≥6 seconds.
• Reproducibility: The two largest FVC and FEV1 values must be within 0.150 L of each other.
• Artifact Detection: Review graphs for coughs during the first second, glottis closure, or premature termination. Reject any maneuver exhibiting these artifacts.

Pro Tips & Pitfalls

• Pitfall - The "Slow Start": Many patients hesitate at the beginning. If the peak flow is low, reiterate the need for an explosive, instantaneous start.
• Pro Tip - Coaching: Use active, loud, and encouraging coaching. Phrases like "Blast it out!" and "Keep going, keep going, keep going!" significantly improve patient performance.
• Pitfall - Leakage: Always check the seal around the mouthpiece. If the patient has dentures, leave them in unless they prevent a tight seal.
• Pro Tip - Visual Feedback: If the spirometer screen allows, show the volume-time curve to the patient. Visualizing the "plateau" helps them understand how long they need to keep blowing.

Frequently Asked Questions

Q: What should I do if a patient cannot reach the reproducibility criteria after 8 attempts? A: Stop the procedure to avoid patient fatigue. Note on the report that the results are suboptimal due to lack of reproducibility and record the best efforts obtained. Do not force the patient beyond their physical capability.

Q: Does the patient need to be fasting before spirometry? A: Generally, no. However, it is advisable to avoid a very large meal within 2 hours of the test, as abdominal distension can limit the ability to take a full, deep breath.

Q: How often must the spirometer be calibrated? A: Daily calibration checks are the gold standard. If the calibration syringe readings deviate by more than ±3%, the device should be serviced and must not be used for patient testing until the error is resolved.