title: Assessing PaCO2 in acute respiratory disease: accuracy of a transcutaneous carbon dioxide device.
abstract: 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) < 50% predicted) or suspected pneumonia (fever, cough and respiratory rate >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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Medical Research Institute of New Zealand, University of Otago Wellington, New Zealand.
authors.forename: K
authors.initials: K
authors.lastname: Perrin
authors.forename: M
authors.initials: M
authors.lastname: Wijesinghe
authors.forename: M
authors.initials: M
authors.lastname: Weatherall
authors.forename: R
authors.initials: R
authors.lastname: Beasley
mesh_terms: D000208:Acute Disease; D000328:Adult; D001249:Asthma / Q000097:blood* / Q000175:diagnosis; D001785:Blood Gas Monitoring, Transcutaneous / Q000379:methods / Q000592:standards; D002245:Carbon Dioxide / Q000097:blood*; D017714:Community-Acquired Infections / Q000097:blood / Q000175:diagnosis; D005260:Female; D006801:Humans; D008297:Male; D010092:Oximetry / Q000379:methods / Q000592:standards*; D010313:Partial Pressure; D011014:Pneumonia / Q000097:blood* / Q000175:diagnosis; D011446:Prospective Studies
chemical_list: D002245:Carbon Dioxide