Utility of the expiratory capnogram in the assessment of bronchospasm

M. Yaron*, P. Padyk, M. Hutsinpiller, C. B. Cairns

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

79 Scopus citations


Study objective: To determine whether the plateau phase of the expiratory capnogram (dco2/dt) can detect bronchospasm in adult asthma patients in the emergency department and to assess the correlation between dco2/dt and the peak expiratory flow rate (PEFR) in spontaneously breathing patients with asthma and in normal, healthy volunteers. Methods: We carried out a prospective, blinded study in a university hospital ED. Twenty adults (12 women) with acute asthma and 28 normal adult volunteers (15 women) breathed through the sampling probe of an end-tidal CO2 monitor, and the expired CO2 waveform was recorded. The dco2/dt of the plateau (alveolar) phase for five consecutive regular expirations was measured and a mean value calculated for each patient. The best of three PEFRs was determined. The PEFR and dco2/dt were also recorded after treatment of the asthmatic patients with inhaled β-agonists. Results: The mean±SD PEFR of the asthmatic subjects was 274±96 L/minute (57% of the predicted value), whereas that of the normal volunteers was 527±96 L/minute (103% of the predicted value) (P<.001). The mean dco2/dt of the asthmatic subjects (.26±.06) was significantly steeper than that of the normal volunteers (.13±06) (P<.001). The dco2/dt was correlated with PEFR (r=.84, P<.001). In 18 asthmatic subjects the pretreatment and posttreatment percent predicted PEFRs were 58%±17% and 74%±17%, respectively (P<.001), whereas the dco2/dt values were .27±.05 and .19±.07, respectively (P<.005). Conclusion: The dco2/dt is an effort-independent, rapid, noninvasive measure that indicates significant bronchospasm in ED adult patients with asthma. The dco2/dt value is correlated with PEFR, an effort-dependent measure of airway obstruction. The change in dco2/dt with inhaled β-agonists may be useful in monitoring the therapy of acute asthma.

Original languageEnglish
Pages (from-to)403-407
Number of pages5
JournalAnnals of Emergency Medicine
Issue number4
StatePublished - 1996
Externally publishedYes


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