Development and Preclinical Evaluation of a CPAP-Compatible EtCO2 Sampler

BACKGROUND Capnography is a vital tool in EMS because changes to end-tidal CO 2 (ETCO 2 ) generally precede blood oxygen desaturation, and waveform morphology can be used to assess bronchial patency. Many of capnography’s indications overlap with those of continuous positive airway pressure (CPAP) therapy. However, there is currently no validated method to measure capnography during CPAP administration, and combining the two technologies in the prehospital setting lacks investigation in peer-reviewed literature. METHODS We developed a novel exhalatory CO 2 sampler designed to seamlessly integrate with existing prehospital CPAP systems, manufactured via stereolithography. Using a Human Patient Simulator, we compared this novel sampler in vitro with a traditional nasal-oral cannula (NC), examining the effects of CPAP administration on ETCO 2 , capnogram shape, and respiration rate (RR). RESULTS The CCA maintained an air-tight seal during CPAP administration and showed no significant differences in ETCO 2 values or RR compared to the NC. However, CPAP administration significantly reduced ETCO 2 values and altered capnogram morphology for both samplers. These changes indicate that CPAP itself affects capnography readings, necessitating caution in interpreting these measurements. CONCLUSIONS The novel CCA is a viable tool for integrating capnography with CPAP in prehospital settings, but the effects of CPAP on capnography readings must be further studied. Future research should focus on clinical trials with human subjects to validate these findings and improve the interpretation of capnography data during CPAP therapy.