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(Chest. 2000;118:1378-1381.)
© 2000 American College of Chest Physicians

Routine Pulse Oximetry During Methacholine Challenges Is Unnecessary for Safety*

Donald W. Cockcroft, MD, FCCP; Thomas S. Hurst, MVetSc; Darcy D. Marciniuk, MD, FCCP; David J. Cotton, MD; Karen F. Laframboise, MD; Anil K. Nagpal, MD, FCCP and Robert P. Skomro, MD

* From the Department of Medicine, Division of Respiratory Medicine, Royal University Hospital, University of Saskatchewan, Saskatoon, Canada.

Correspondence to: Donald W. Cockcroft, MD, FCCP, Division of Respiratory Medicine, Royal University Hospital, 103 Hospital Dr, Ellis Hall, Room 551, Saskatoon, SK S7N 0W8 Canada; e-mail: cockcroft{at}sask.usask.ca

Background: Methacholine-induced bronchoconstriction is associated with significant hypoxemia, which can be assessed noninvasively by transcutaneous oxygen tension and pulse oximetry.

Objectives: To assess the value of the monitoring of finger pulse oximetry during routine methacholine challenges in a clinical pulmonary function laboratory with regard to both safety and the possibility that a significant fall in oxygen saturation as measured by pulse oximetry (SpO2) might be a useful surrogate for determining the response to methacholine.

Methods: Two hundred consecutive patients undergoing diagnostic methacholine challenges in the pulmonary function laboratory of a tertiary-care, university-based referral hospital were studied. Methacholine challenges were performed by the standardized 2-min tidal breathing technique, and the {Delta}FEV1 was calculated from the lowest postsaline solution inhalation to the lowest postmethacholine inhalation value. SpO2 was measured immediately prior to each spirogram, and the {Delta}SpO2 was measured from the lowest postsaline solution inhalation value to the lowest postmethacholine inhalation value. We examined the data for safety (ie, any SpO2 value < 90). Based on previous reports, we used a {Delta}SpO2 of >= 3 as significant and looked at the sensitivity, specificity, and positive and negative predictive values for {Delta}SpO2 >= 3 vis-à-vis a fall in FEV1 of >= 15%.

Results: There were 119 nonresponders ({Delta}FEV1, < 15%) and 81 responders. The baseline FEV1 percent predicted was slightly but significantly lower in the responders (responders [± SD], 91.6 ± 15%; nonresponders, 96.4 ± 14%; p < 0.05). {Delta}SpO2 was 3.1 ± 1.6 in the responders and 1.6 ± 1.8 in the nonresponders (p < 0.001). There was a single recording in one patient of SpO2 < 90 (88). A {Delta}SpO2 >= 3 had a sensitivity of 68%, a specificity of 73%, a positive predictive value of 63%, and negative predictive value of 77% for a fall in FEV1 >= 15%.

Conclusions: Pulse oximetry is not routinely useful for safety monitoring during methacholine challenge. {Delta}SpO2 is not helpful in predicting a positive spirometric response to methacholine. However, the negative predictive value is adequate to allow the {Delta}SpO2 to be used as an adjunct in assessing a negative result of a methacholine test in patients who have difficulty performing spirometry.

Key Words: asthma • methacholine test • oxygen saturation






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Copyright © 2000 by the American College of Chest Physicians.