Standardisation facilitates reliable interpretation of ETCO₂ during manual cardiopulmonary resuscitation

Interpretation of end-tidal CO₂ (ETCO₂) during manual cardiopulmonary resuscitation (CPR) is affected by variations in ventilation and chest compressions. This study investigates the impact of standardising ETCO₂ to constant ventilation rate (VR) and compression depth (CD) on absolute values and trends.

Retrospective study of out-of-hospital cardiac arrest cases with manual CPR, including defibrillator and clinical data. ETCO₂, VR and CD values were averaged by minute. ETCO₂ was standardised to 10 vpm and 50 mm. We compared standardised (ET_s) and measured (ET_m) values and trends during resuscitation.

Of 1,036 cases, 287 met the inclusion criteria. VR was mostly lower than recommended, 8.8 vpm, and highly variable within and among patients. CD was mostly within guidelines, 49.8 mm, and less varied. ET_s was lower than ET_m by 7.3 mmHg. ET_s emphasized differences by sex (22.4 females vs. 25.6 mmHg males), initial rhythm (29.1 shockable vs. 22.7 mmHg not), intubation type (25.6 supraglottic vs. 22.4 mmHg endotracheal) and return of spontaneous circulation (ROSC) achieved (34.5 mmHg) vs. not (20.1 mmHg). Trends were different between non-ROSC and ROSC patients before ROSC (-0.3 vs. + 0.2 mmHg/min), and between sustained and rearrest after ROSC (-0.7 vs. -2.1 mmHg/min). Peak ET_s was higher for sustained than for rearrest (53.0 vs. 42.5 mmHg).

Standardising ETCO₂ eliminates effects of VR and CD variations during manual CPR and facilitates comparison of values and trends among and within patients. Its clinical application for guidance of resuscitation warrants further investigation.