Capnography for monitoring non-intubated spontaneously breathing patients in an emergency room setting

Abstract

Objective - To examine the feasibility of using expiratory capnography as an indicator of airway obstruction in non-intubated resuscitation room patients. Methods - Patients with potential respiratory compromise admitted to the resuscitation room were assessed for widespread expiratory wheeze. This was taken as clinical evidence of airways obstruction. Expiratory capnograms of these patients and patients who had no wheeze were obtained. The traces were analysed for basic morphology and where appropriate the slope ratio (SR) between phase 1 (S1) and phase 2 (S2) of the trace was obtained. Results - Thirty eight patients with a variety of clinical conditions causing potential or actual respiratory impairment were studied. All patients tolerated the nasal capnogram cannulae. Twelve had no clinical evidence of airway obstruction and all had capnograms with normal morphology. Eleven of these were analysed further. The mean value for SR was 7.57 (SEM 0.18), 95% confidence interval 6.37 to 8.77. Twenty six patients had clinical evidence of airway obstruction. The capnograms showed obstructive "shark's fin" morphology. Fourteen of these were analysed to determine SR. The mean value was 31.9 (4.46), 95% CI 22.9 to 40.8. There was a significant difference in the mean value for SR between the two groups (P ≪ 0.001). Conclusions - Capnography may be used as a means of continuous respiratory monitoring in non-intubated acutely ill patients. Capnogram analysis may be used to indicate airway obstruction in these patients. Further work is required to correlate curve indices to degree of airway obstruction.