LAUSR

BACKGROUND Real-time measurement of end-tidal carbon dioxide (ETCO2) is used as a non-invasive estimate of cardiac output and perfusion during cardiopulmonary resuscitation (CPR). However, capnograms are often distorted by chest compressions (CCs) and this may affect ETCO2 measurement. The aim of the study was to quantify the effect of CC-artefact on the accuracy of ETCO2 measurements obtained during out-of-hospital manual CPR. METHODS We retrospectively analysed monitor-defibrillator recordings collected by two advanced life support agencies during out-of-hospital cardiac arrest. These two agencies, represented as A and B used different side-stream capnometers and monitor-defibrillators. One-minute capnogram segments were reviewed. Each ventilation within each segment was identified using the transthoracic impedance signal and the capnogram. ETCO2 values per ventilation were manually annotated and compared to the corresponding capnometry values stored in the monitor-defibrillator. Ventilations were classified as distorted or non-distorted by CC-artefact. RESULTS A total of 407 1-min capnogram segments from 65 patients were analysed. Overall, 4,095 ventilations were annotated, 2,170 (32.4% distorted) and 1,925 (31.8% distorted) for agency A and B, respectively. Median (IQR) unsigned error in ETCO2 measurement increased from 1.5 (0.6-3.1)% for non-distorted to 5.5 (1.8-14.1)% for distorted ventilations; from 0.7 (0.3-1.2)% to 3.7 (1.0-9.9)% in agency A and from 2.3 (1.2-3.9)% to 8.3 (3.9-19.5)% in agency B (p<0.001). Errors were higher than 10mmHg in 9% and higher than 15mmHg in 5% of the distorted ventilations. CONCLUSION CC-artefact causes ETCO2 measurement errors in the two studied devices. This suggests that capnometer algorithms may need to be adapted to reliably perform in the presence of CC-artefact during CPR.