ATS Pulmonary Function Laboratory Manual

CHAPTER  12

Table 12.4

Dilution Schedule for Quadrupling Concentrations

Label Strength

Take

Add Diluent

Obtain Dilution

100 mg

100 mg

6.25 ml

16 mg/ml 4 mg/ml 1 mg/ml 0.25 mg/ml

3 ml of 16 mg/ml 3 ml of 4 mg/ml 3 ml of 1 mg/ml 3 ml of 0.25 mg/ml

9 ml 9 ml 9 ml 9 ml

0.0625 mg/ml

3.4.

Storage of diluted methacholine solutions 3.4.1.

Methacholine solutions should be stored in a refrigerator (4° C). At this temperature, higher concentrations (i.e., >1.25 mg/ml) have been reported to be stable for at least 15 weeks (15–19). According to the package insert, Provocholine ® solutions are stable for up to 2 weeks when stored at 36° to 46° F (2° to 8 ° C). If using Provocholine ® , the package insert instructions should be followed. Each vial of methacholine solution should be clearly labeled with the drug name, concen- tration of the diluent, date prepared, date expired, and initials of individual preparing the solution. For example: Methacholine 2.5 mg/ml Diluent: 0.9% NaCl Prepared: 12/16/17 by XYZ (initials of person making solutions) Expires: 12/30/17

3.4.2.

3.4.3.

RECOMMENDED EQUIPMENT FOR TIDAL BREATHING METHOD (10). The 1999 ATS guidelines (3) recommended the English Wright nebulizer for the tidal breathing technique and the DeVilbiss 646 for the 5-breath dosimeter method. Both these devices would be considered obsolete by modern standards. Furthermore, the bronchodilator effect of the inspiration from FRC to TLC with the 5-breath dosimeter technique has been shown to blunt the response to methacholine and give rise to false negative results (7). When comparing the results from one nebulizer to another, the dose delivered to the lung gives rise to similar results, which is not the case with the concentration used, which favors the use of the cumulative dose of methacholine that causes a fall of 20% for the FEV 1 . There are data that allow the comparison of the English Wright to a breath- actuated nebulizer, and manufacturers should be able to supply data allowing the calculation of the dose delivered to the lungs for each concentration. 4.1. Nebulizer 4.1.1. Use a high-quality nebulizer that generates aerosols with a particle size of ≤ 5 μ m. The perfor- mance characteristics must be measured and both the technique and results reported by the manufacturer (10). 4.1.2. Use the same nebulizer throughout a challenge because of inter-nebulizer output variability.

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