• Scott Farenden, Yewon Chung, Amy Cui, and Ian Ferguson.
• Emergency Department, Liverpool Hospital, Liverpool, New South Wales, Australia.
• Emerg Med J. 2023 Sep 1; 40 (9): 646650646-650.

BackgroundTranscutaneous 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.MethodsThis 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.ResultsDuring 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.ConclusionThe 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.© Author(s) (or their employer(s)) 2023. No commercial re-use. See rights and permissions. Published by BMJ.

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