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Prospective, observational study investigating the level of agreement between transcutaneous and invasive carbon dioxide measurements in critically ill emergency department patients
  1. Scott Farenden1,
  2. Yewon Chung2,3,
  3. Amy Cui1,
  4. Ian Ferguson1,4
  1. 1 Emergency Department, Liverpool Hospital, Liverpool, New South Wales, Australia
  2. 2 Department of Respiratory and Sleep Medicine, Liverpool Hospital, Liverpool, New South Wales, Australia
  3. 3 South Western Sydney Clinical School, University of New South Wales, Sydney, New South Wales, Australia
  4. 4 Ambulance Service of NSW, Rozelle, New South Wales, Australia
  1. Correspondence to Dr Amy Cui, Emergency, Liverpool Hospital, Liverpool, NSW 2170, Australia; amy.cui{at}


Background Transcutaneous carbon dioxide (Ptcco2) measurement is a non-invasive surrogate marker for arterial carbon dioxide (Paco2), which requires invasive arterial blood sampling. Use of Ptcco2 has been examined in different clinical settings, however, most existing evidence in the adult emergency department (ED) setting shows insufficient agreement between the measurements. This study assessed the level of agreement between Ptcco2 and Paco2 in undifferentiated adult ED patients across multiple timepoints.

Methods This prospective observational study (study period 2020–2021) assessed paired Ptcco2 and Paco2 measurements at four consecutive timepoints (0, 30, 60 and 90 min) in adult (aged 18 years or over) Australian ED patients requiring hospital admission and arterial catheter insertion. Agreement between the pairs was assessed using Bland-Altman analysis. It was prospectively determined by expert consensus that limits of ±4 mm Hg would be a clinically acceptable level of agreement between Ptcco2 and Paco2.

Results During the study period 168 paired Ptcco2 and Paco2 readings were taken from 42 adult ED patients. Bland-Altman analysis showed a mean Ptcco2 reading 3.85 mm Hg higher than Paco2, although at each timepoint the 95% CIs breached the limit of 4 mm Hg difference. In addition, only 66% (111/168) of results fell within the clinically acceptable range.

Conclusion The level of agreement between Ptcco2 and Paco2 measurements may not be sufficiently precise for the adoption of Ptcco2 monitoring in patients presenting to the ED.

  • critical care
  • emergency department
  • respiratory
  • arterial
  • ventilation

Data availability statement

No data are available.

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  • Handling editor Mary Dawood

  • Contributors This study was conceived and designed by all four authors. Data was collected in the emergency department by IF, SF and AC. Data analysis was performed by SF. The paper was written by all four authors—IF, YC, SF and AC. The guarantor for this study is SF.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.