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Clinical Investigations: INHALATION |

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; Robert P. Skomro, MD
Author and Funding Information

*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@sask.usask.ca



Chest. 2000;118(5):1378-1381. doi:10.1378/chest.118.5.1378
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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 ΔFEV1 was calculated from the lowest postsaline solution inhalation to the lowest postmethacholine inhalation value. Spo2 was measured immediately prior to each spirogram, and theΔ 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 ΔSpo2 of ≥ 3 as significant and looked at the sensitivity, specificity, and positive and negative predictive values for ΔSpo2 ≥ 3 vis-à-vis a fall in FEV1 of ≥ 15%.

Results: There were 119 nonresponders (ΔFEV1,< 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). ΔSpo2 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 ΔSpo2 ≥ 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.Δ Spo2 is not helpful in predicting a positive spirometric response to methacholine. However, the negative predictive value is adequate to allow the ΔSpo2 to be used as an adjunct in assessing a negative result of a methacholine test in patients who have difficulty performing spirometry.


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