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Predefibrillation end-tidal CO2 and defibrillation success in out-of-hospital cardiac arrest: an observational cohort study
  1. Jonathan L Kwong1,
  2. Ian R Drennan2,3,
  3. Linda Turner4,
  4. Sheldon Cheskes3,4
  1. 1Division of Emergency Medicine, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
  2. 2Sunnybrook Research Institute, Toronto, Ontario, Canada
  3. 3Department of Family and Community Medicine, University of Toronto, Toronto, Ontario, Canada
  4. 4Sunnybrook Centre for Prehospital Medicine, Toronto, Ontario, Canada
  1. Correspondence to Dr Jonathan L Kwong, Division of Emergency Medicine, University of Toronto Faculty of Medicine, Toronto M8W 3S2, Canada; jon.kwong{at}


Background Predefibrillation end-tidal CO2 (ETCO2) may predict defibrillation success and could guide defibrillation timing in ventricular fibrillation (VF) cardiac arrest. This relationship has only been studied using advanced airways. Our aim was to evaluate this relationship using both basic (bag–valve–mask (BVM)) and advanced airways (supraglottic airways and endotracheal tubes).

Methods Prehospital patient records and defibrillator files were abstracted for patients with out-of-hospital cardiac arrest in Ontario, Canada, with initial VF cardiac rhythms between 1 January 2018, and 31 December 2019. Analyses assessed the relationship between each predefibrillation ETCO2 reading and defibrillation outcomes at the subsequent 2 min pulse check (ie, VF, asystole, pulseless electrical activity (PEA) or return of spontaneous circulation (ROSC)), accounting for airway types used during resuscitation. Multivariable logistic regression evaluated the association between the first documented predefibrillation ETCO2 and postshock VF termination or ROSC.

Results Of 269 cases abstracted, 153 had predefibrillation ETCO2 measurements and were included in the study. Among these cases, 904 shocks were delivered and 44.4% (n=401) had predefibrillation ETCO2 measured. The first ETCO2 reading was more often from BVM (n=134) than advanced airways (n=19). ETCO2 readings were lower when measured through BVM versus advanced airways (30.5 mm Hg (4.06 kPa) (±14.4 mm Hg (1.92 kPa)) vs 42.1 mm Hg (5.61 kPa) (±22.5 mm Hg (3.00 kPa)), adjANOVA p<0.01). Of all shocks with ETCO2 reading (n=401), no difference in preshock ETCO2 was found for subsequent shocks that resulted in persistent VF (32.2 mm Hg (4.29 kPa) (±15.8 mm Hg (2.11 kPa))), PEA (32.8 mm Hg (4.37 kPa) (±17.1 mm Hg (2.30 kPa))), asystole (32.4 mm Hg (4.32 kPa) (±20.6 mm Hg (2.75 kPa))) or ROSC (32.5 mm Hg (4.33 kPa) (±15.3 mm Hg (2.04 kPa))), analysis of variance p=0.99. In the multivariate analysis using the initial predefibrillation ETCO2, there was no association with VF termination on the subsequent shock (adjusted OR (adjOR) 0.99, 95% CI 0.97 to 1.02, p=0.57) or ROSC (adjOR 1.00, 95% CI 0.97 to 1.03, p=0.94) when evaluated as a continuous or categorical variable.

Conclusion Predefibrillation ETCO2 measurement is not associated with VF termination or ROSC when basic and advanced airways are included in the analysis. The role of predefibrillation ETCO2 requires careful consideration of the type of airway used during resuscitation.

  • resuscitation
  • airway

Data availability statement

Data may be obtained from a third party and are not publicly available.

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Data availability statement

Data may be obtained from a third party and are not publicly available.

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  • Handling editor Edward Carlton

  • Contributors All authors were responsible for the conceptualisation, planning, writing and editing of the manuscript. JLK, LT and SC obtained the dataset and assisted in its preparation for abstraction. JLK was responsible for the data abstraction. JLK and IRD were responsible for the statistical analyses. IRD and SC were responsible for project supervision. JLK is responsible for the overall content of the study as guarantor.

  • Funding SC received investigator-initiated grant funding from Zoll Medical for AED on the Fly, Improving Community Response to Cardiac Arrest and Monitoring Ventilation during out of Hospital Cardiac Arrest research studies. SC received speaker’s honorarium for educational events on cardiopulmonary resuscitation quality from Zoll Medical. SC sits on the advisory board of Drone Delivery Canada.

  • Competing interests None declared.

  • Patient and public involvement Patients and/or the public were not involved in the design, conduct, reporting or dissemination plans of this research.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.