The Science Journal of the American Association for Respiratory Care

1995 OPEN FORUM Abstracts

The Ph Of Solutions Used For Methacholine Challenge

DM Laskowski RPFT, MK Kavuru MD, HP Wiedemann MD, A Arroliga MD, M Oleksiuk RHP, K McCarthy RCPT, Dept. of Pulmonary and Critical Care Medicine, The Cleveland Clinic Foundation, Cleveland, OH 44195.

Methacholine chloride solution for use in inhalation challenge testing is diluted in physiologic saline solution (0.90% NaCl) or a buffered solution of 0.50% saline, 0.245% sodium bicarbonate, 0.4% phenol in sterile water. In order to evaluate the pH of these two solutions, we measured pH at baseline without methacholine chloride in solution, and at five concentration levels. A Fisher Scientific Accumet pH meter (Model 3 815MP) was used. It was calibrated at 7.00 ( + 0.01) and 4.00 (0.01) using Fisher Scientific pH buffer solution, traceable to National Institute of Standards and Technology. The physiological saline solution (Baxter Pharmaceuticals) has a pH range of 4.50 to 7.00 (0.05 molar). The results are compared in graph below.


The results show a uniform decrease in pH as the concentration of methacholine increases in the diluent with physiological saline, while the pH of the buffered methacholine chloride solution remains stable.

We conclude 1) The buffered solution yields a stable pH in the range of 7.78 to 8.00. 2) The pH of the non-buffered saline solution varies with the concentration of methacholine chloride dissolved in solution (range 3.95 to 5.29) 3) The pH of the buffered solution and the pH of the saline solution vary significantly; this variation may affect the assessment of bronchial hyperresponsiveness.


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