ATS Pulmonary Function Laboratory Manual

ATS Pulmonary Function Laboratory Management & Procedure Manual | 3rd Edition

2.

Interpretation 2.1. Commonly, the methacholine challenge is interpreted categorially as either demonstrating airway hyperresponsiveness or not. 2.2. Based on the 1999 ATS guideline, and for the 2-minute tidal breathing technique using twofold increases in concentrations, the PC 20 FEV 1 cutoff between hyperresponsive and nonhyperrespon- sive airways ranges from 4 to 16 mg/ml (30–34). 2.3 Recommendations from 2017 ERS guideline (10) using PD 20 , and based on 2 minutes of nebuliza- tion using English Wright nebulizer are as follows:

PD 20

PC 20

(μmole)

μg

(mg/ml)

Interpretation

>2

>400

>16

normal AHR

0.5–2.0 0.13–0.5 0.03–0.13

100–400 25–100

4–16

borderline AHR

1–4

mild AHR

6–25

0.25–1

moderate AHR marked AHR

<0.03

<6

<0.25

AHR = airway hyperresponsiveness.

3.

Safety and Training 3.1 The technician performing the methacholine challenge should: 1. Be trained in spirometry and performing the challenge 2. Receive approximately 4 days of hands-on training and perform at least 20 supervised tests to become proficient 3. Be familiar with safety and emergency procedures 4. Wash their hands before and after handling the equipment and testing 5. Minimize exposure to aerosolized methacholine and strongly consider not performing this test if they have asthma or symptoms suggestive of hyperreactive airways. The use of a breath- actuated nebulizer will minimize environmental methacholine since aerosol is produced only during inspiration. 3.2 The medical director of the laboratory, another physician, or another person appropriately trained to treat acute bronchoconstriction, including appropriate use of resuscitation equipment, must close enough to respond quickly to an emergency. 3.3 Patients should never be left unattended during the test procedure. 3.4 O 2 and appropriate O 2 tubing will be readily available in the testing room. Also, a stethoscope and sphygmomanometer to auscultate the chest and to measure blood pressure, and a pulse oximeter to ensure adequate O 2 delivery should be available. 3.5 Medications to treat an acute bronchospasm attack should also be present in the testing room, in- cluding epinephrine for subcutaneous injection, and albuterol and ipratropium bromide in metered dose inhaler and/or in premixed solutions.

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