The lack of a role for saline solution inhalation in bronchoprovocation challenge

The purpose of this study was to look prospectively at the practice of prefacing methacholine bronchoprovocation challenge (BPC) with diluent challenge using physiologic saline solution (NaCl) as the diluent. We wished to determine whether NaCl challenge added to the safety or diagnostic accuracy of BPC. We studied 108 consecutive patients undergoing methacholine BPC. We determined (1) the FEV1 response of all patients to the inhalation of NaCl (the difference between the FEV1 before NaCl and the FEV1 after NaCl), and (2) the correlation between the response to saline solution and bronchial hyperresponsiveness (BHR) measured using methacholine. Paired Student's t testing demonstrated a small but significant difference between the values for FEV1 before and after NaCl for the group as a whole (n = 108; mean change, -0.9 +/- 4 percent [+/- SD]; p = 0.023). When the mean changes in the FEV1 after NaCl for the group with increased BHR (BHR+) (n = 62; mean, -1.1 +/- 4.9 percent) and the group with no increase in BHR (BHR-) (n = 46; mean, -0.6 +/- 2.4 percent) were contrasted, there was no significant difference between the two groups (p = 0.46). Only 4 of 108 patients had a drop in FEV1 of 10 percent or more after NaCl, with the greatest drop being 16 percent. All four patients were BHR+, but none had marked BHR. For the BHR+ group, there was no correlation between response to saline solution and subsequent response to methacholine (r = 0.02). We conclude that saline solution challenge adds time and expense to BPC without increasing the safety or yield of BPC. We suggest that NaCl challenge can be omitted from the standard performance of BPC.