Use of capnographic waveform indices in monitoring non - intubated asthmatic patients within the emergency department

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Date
2001-11
Authors
Teo, Aik Howe
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Publisher
Universiti Sains Malaysia
Abstract
To determine if the slope of Phase II and Phase Ill, and the alpha angle (Angle Q) of the expiratory capnographic waveform measured via computerrecognizable algorithms, can reflect changes in bronchospasm in acute asthmatic patients presenting to the Emergency Department; and to assess the correlation of these changes with clinical severity scoring and peak flow measurements. We carried out a prospective study in a university hospital Emergency Department. 30 patients with acute asthma were monitored with clinical severity scoring (speech pattern, respiratory rate, pulse rate, presence of pulsus paradoxus and wheeze, and pulse oximetry) and peak flow measurements, and then had a nasal cannula attached for sidestream sampling of expired carbon dioxide. The capnographic waveform was recorded onto a PC card for analysis. The patients were treated with inhaled beta-agonists and steroids according to departmental protocols. After treatment, when they were adjudged well for discharge, a second set of results was obtained for clinical severity scoring, peak flow measurements and capnographic waveform recording. The pre-treatment and post-treatment results were then compared with paired samples t-test analysis. Sin1ple and canonical correlations were performed to determine correlations between the 3 assessment methods. A p value of below 0.05 was taken to be significant. There was significant improvements pre-treatment and post-treatment in 4 parameters in the clinical severity scoring, namely speech pattern (p = 0.002), pulsus paradoxus (p = 0.007), wheeze {p < 0.001) and pulse oximetry (p = 0.035); but there was no significant difference in pulse rates (p = 0.052) or respiratory rates (p = 0. 739). Similarly, peak flow measurements also showed significant improvements post-treatment (p < 0.001). On the capnographic waveform, there was a significant difference in the slope of Phase Ill (p < 0.001) and alpha angle {p < 0.001); but not in Phase II slope (p = 0.35). Correlation studies done between all three assessment methods did not show strong correlations neither between the measurements itself nor the magnitude of change pre-treatment and post-treatment. Clinical severity scoring, peak flow measurements and capnographic waveform indices can indicate improvements airway diameter in acute asthmatics within the Emergency Department. Capnographic waveform analysis presents several advantages in that it is effort-independent, and provides continuous monitoring of normal tidal respiration. They can be proposed for the monitoring of asthmatics within the Emergency Department when specific computerised indices can instantly analyse the capnographic waveform and report the indices in a recognizable and reproducible form.
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Keywords
Capnographic waveform, acute asthma
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