An exploratory feasibility study of a novel portable mainstream capnograph in a prehospital environment

Background Monitoring end-tidal carbon dioxide (EtCO 2 ) and respiratory rate (RR) is a non-invasive and reliable, continuous breathing assessment method in intubated and spontaneously breathing patients. The prehospital spreading of this technique in awake patients has been limited by mainstream capnographs´ dimensions and costs. Yet the potential prehospital applications of a wearable mainstream capnograph are many. This study aims to assess the ability to measure EtCO 2 of the novel mainstream MARIE capnograph in normal ambulance transport conditions. Methods A single-centre, observational, exploratory feasibility study conducted in Region Uppsala between December 2024 and January 2025. First 20 healthy adult volunteers were transported approximately 10 min by ambulance, having EtCO 2 and RR continuously measured by the mainstream device. Three measurements were performed (in the beginning, in the middle and at the end of the transport). A fourth value was noted on arrival in the Emergency Department (ED) with a reference capnograph for comparison with the third value by the mainstream device. The same measurement procedure was then repeated on 30 clinically stable adult patients transported by ambulance to the ED. Results A total of 20 volunteers and 29 patients were included in the final analysis. The comparison between the mainstream and reference capnograph showed that median EtCO 2 values were 4.6 [4.1–5.2] vs. 4.9 [4.4–5.2] kPa respectively ( p = 0.35). Bland Altman analysis showed a mean difference between the mainstream capnograph and reference device of 0.16 kPa (95% CI -0.07-0.41), with moderate correlation between measurements. The median values of breaths per minute were 17 [14–21] vs. 19 [15–22] respectively ( p < 0.01). Conclusion This study suggests that the mainstream capnograph MARIE is able to measure credible EtCO 2 values in standard ambulance transport conditions. Clinical trial registration ClinicalTrials.gov, TRN NCT06905613, Registration date 16th December 2024.