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Background Pulse oximetry non-invasively assesses the arterial oxygen saturation of patients with acute respiratory disease; however, measurement of the arterial partial pressure of carbon dioxide (PaCO(2)) requires an arterial blood gas. The transcutaneous partial pressure of carbon dioxide (PtCO(2) ) has been used in other settings with variable accuracy. We investigated the accuracy of a PtCO(2) device in the assessment of PaCO(2) in patients with asthma and suspected pneumonia attending the emergency department. Methods Patients with severe asthma (FEV(1) 18/min) were enrolled. Subjects were excluded if they had a history of chronic obstructive pulmonary disease or other conditions associated with respiratory failure. Arterial blood gases were taken at the discretion of the investigator according to clinical need, and paired with a simultaneous reading from the PtCO(2) probe. Results Twenty-five patients were studied with one set of data excluded because of poor PtCO(2) signal quality. The remaining 24 paired samples comprised 12 asthma and 12 pneumonia patients. The range of PaCO(2) was 19-64 mmHg with a median of 36.5 mmHg. Bland-Altman analysis showed a mean (SD) PaCO(2) - PtCO(2) difference of -0.13 (1.9) mmHg with limits of agreement of plus or minus 3.8 mmHg (-3.9 to +3.7). Conclusion A PtCO(2) device was accurate in the assessment of PaCO(2) in patients with acute severe asthma and suspected pneumonia when compared with an arterial blood gas. These bedside monitors have the potential to improve patient care by non-invasively monitoring patients with acute respiratory disease at risk of hypercapnia.

Background: High concentration oxygen is commonly administered during acute exacerbations of chronic obstructive pulmonary disease (AECOPD). The aim of this study was to determine the association between oxygen, severity markers and poor outcomes in AECOPD. Methods: In an audit of patients with AECOPD arriving by ambulance to the Emergency Department of Wellington Hospital, details of oxygen administration, clinical outcomes and severity markers were documented. The main outcome measure was a composite of death, assisted ventilation, or respiratory failure. Associations between oxygen therapy, severity markers and poor clinical outcomes were assessed by logistic regression. Results: Of 250 patients 77 (31%) died, required assisted ventilation or were in respiratory failure. Increased oxygen flow was associated with increasing risk of death, assisted ventilation or respiratory failure with an odds ratio (OR) of 1.2 (95% CI 1.0–1.4) per 1 L/min oxygen flow. Increasing PaO2 was associated with a greater risk of a poor outcome with an OR of 1.1 (95% CI 1.0–1.3) per 10 mmHg higher PaO2. Home oxygen (OR 2.8, 95% CI 1.5–5.1), previous respiratory failure (OR 2.6, 95% CI 1.5–4.6), previous ventilation (OR 3.2, 95% CI 1.7–5.9) and home nebulizer use (OR 2.4, 95% CI 1.4–4.3) were associated with an increased risk of a poor outcome. Conclusion: In AECOPD high flow oxygen in the ambulance is associated with poor clinical outcomes. A number of easily identified markers of chronic disease severity indicate an increased risk of a poor clinical outcome.