Aim: Chest compressions (CCs) generate oscillations in time-capnograms during cardiopulmonary resuscitation. In a previous study, we have classified oscillations into three categories: type I and type III during capnogram plateau, type II during baseline [1]. Causes of this phenomenon are poorly understood. Here we analyzed interactions between capnogram oscillations and ventilatory airflow and volume waveforms during CCs.
Methods: Signals were recorded during adult cardiac arrest cases at the Department of Emergency Medicine, Medical University of Vienna (Austria) [2]. Segments with simultaneous manual CCs and ventilations after patient intubation were analysed, retrospectively. We examined patterns of CC artefacts in the capnogram, airflow and volume. Inspiration and expiration phases were marked in the airflow. We annotated reversed airflow (RF) occurrences, i.e. changes in airflow sign caused by CCs [3], and analysed their effect on capnograms.
Results: A total of 1414 ventilations from 4 patients (all males, 3 ROSC) were studied. Due to the small number of patients, a descriptive analysis of the observations is provided. When the airflow was negligible (between consecutive ventilations), spikes in airflow originated by CCs generated small volumes (passive ventilations) causing oscillations in the capnogram plateau (in 70% of ventilations). During positive (inspiration) and negative (expiration) airflow, CCs originated RF in 3 patients (80%). Only when RF caused noticeable volume drops during inspiration (or volume rises during expiration), did this result in significant rises (or drops) in CO2 concentration (type II, 2% of ventilations). The figure illustrates RF causing CO2 oscillations: during inspiration (ventilations 1 and 3) and in the plateau (1 and 2).
Conclusion: Manual CCs distort airflow during manual ventilation, frequently causing reversed airflow. Capnogram oscillations in the respiratory baseline are caused by airflow reversal sufficient to generate significant volume changes.
[1] Leturiondo. Resuscitation 2018;124:63-8.
[2] Hubner. AJEM 2020;38:526-33.
[3] Duchatelet. Resuscitation 2018;129:97-102.

Qualitative analysis of capnogram oscillations caused by manual chest compressions: the role of reversed airflow

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