Intrathoracic Airway Closure Impacts CO2 Signal and Delivered Ventilation during Cardiopulmonary Resuscitation

Domenico L Grieco, Laurent J Brochard, Adrien Drouet, Irene Telias, Stéphane Delisle, Gilles Bronchti, Cecile Ricard, Marceau Rigollot, Bilal Badat, Paul Ouellet, Emmanuel Charbonney, Jordi Mancebo, Alain Mercat, Dominique Savary, Jean-Christophe M Richard

Research output: Contribution to journalArticlepeer-review


RATIONALE: End-tidal CO2 (EtCO2) is used to monitor cardiopulmonary resuscitation (CPR), but it can be affected by intrathoracic airway closure. Chest compressions induce oscillations in expired CO2, and this could reflect variable degrees of airway patency.

OBJECTIVES: To understand the impact of airway closure during CPR, and the relationship between the capnogram shape, airway closure, and delivered ventilation.

METHODS: This study had three parts: 1) a clinical study analyzing capnograms after intubation in patients with out-of-hospital cardiac arrest receiving continuous chest compressions, 2) a bench model, and 3) experiments with human cadavers. For 2 and 3, a constant CO2 flow was added in the lung to simulate CO2 production. Capnograms similar to clinical recordings were obtained and different ventilator settings tested. EtCO2 was compared with alveolar CO2 (bench). An airway opening index was used to quantify chest compression-induced expired CO2 oscillations in all three clinical and experimental settings.

MEASUREMENTS AND MAIN RESULTS: A total of 89 patients were analyzed (mean age, 69 ± 15 yr; 23% female; 12% of hospital admission survival): capnograms exhibited various degrees of oscillations, quantified by the opening index. CO2 value varied considerably across oscillations related to consecutive chest compressions. In bench and cadavers, similar capnograms were reproduced with different degrees of airway closure. Differences in airway patency were associated with huge changes in delivered ventilation. The opening index and delivered ventilation increased with positive end-expiratory pressure, without affecting intrathoracic pressure. Maximal EtCO2 recorded between ventilator breaths reflected alveolar CO2 (bench).

CONCLUSIONS: During chest compressions, intrathoracic airway patency greatly affects the delivered ventilation. The expired CO2 signal can reflect CPR effectiveness but is also dependent on airway patency. The maximal EtCO2 recorded between consecutive ventilator breaths best reflects alveolar CO2.

Original languageEnglish
Pages (from-to)728-737
Number of pages10
JournalAmerican Journal of Respiratory and Critical Care Medicine
Issue number6
Publication statusPublished - Mar 15 2019
Externally publishedYes


  • Aged
  • Aged, 80 and over
  • Airway Obstruction/physiopathology
  • Carbon Dioxide/metabolism
  • Cardiopulmonary Resuscitation
  • Exhalation/physiology
  • Female
  • Humans
  • Male
  • Middle Aged
  • Out-of-Hospital Cardiac Arrest/therapy
  • Respiration, Artificial
  • Signal Transduction/physiology


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