ATS Pulmonary Function Laboratory Manual

CHAPTER  12

Test Procedure

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Diluent Step

Watch the patient to ensure that he/she is breathing comfortably and quietly, and not tipping the nebulizer. After the appropriate time or breath number for that nebulizer, turn off the compressed air source and take the nebulizer from the patient. Perform post-diluent spirometry at 30 and 90 seconds after nebulization is completed. Obtain acceptable quality FVC test maneuvers at each time point. This may require repeated attempts. Full FVC efforts lasting at least 6 seconds should be performed after administration of the diluent. Calcu- late a target FEV 1 that indicates a 20% fall in FEV 1 (i.e., FEV 1 × 0.80) using the post-diluent data. The diluent should not cause significant change from the pre-challenge testing spirometry. If the FEV 1 has changed by less than ±10% from the pre-challenge FEV 1 , proceed to administer the first dose of methacho- line in the same manner the diluent was administered. If the FEV 1 has increased or decreased at least 10% after diluent, repeat the diluent step. If the FEV 1 has decreased by 20% or more after diluent, the challenge should be cancelled. Empty the remaining diluent from the nebulizer by shaking excess diluent into wastebasket or sink. Withdraw 2–3 ml or appropriate amount of the starting concentration of methacholine, and place it in the same nebulizer used for the diluent. A starting dose of 1–3 μg is considered safe in the routine testing environ- ment where patients have normal or near-normal spirometry and no significant bronchodilator response. With nose clip in place, aerosolize the methacholine using the same nebu- lizer used for diluent. Nebulization time should be the same for each step and appropriate for the chosen nebulizer (e.g., 2 minutes, or 60 seconds). Start timer. Perform post-methacholine spirometry at 30 and 90 seconds after nebuli- zation is completed. Obtain an acceptable quality FEV 1 at each time point. Perform no more than 3 or 4 test maneuvers after each dose. Obtaining a full FVC is not required if FEV 1 is the only outcome. If abbreviated expiratory time is used, care should be taken to assure the inspiration is complete. If other spirometric outcome variables are used or if vocal cord dysfunction is suspected, full FVC maneuvers including inspiration should be performed throughout the test. In order to keep the cumulative effect of methacholine relatively constant, the time interval between the commencement of two serial concentrations is important and should be kept constant at 5 minutes. At each dose, report the highest FEV 1 from acceptable test maneuvers. If the highest post-methacholine FEV 1 falls less than 20% from the post- diluent value (i.e., above target value) go to next step.

First Dose of Methacholine Aerosolization Step

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