Abstract
Background Capnography has recently become the standard-of-care for EMS personnel during out-of-hospital resuscitation to confirm tracheal tube (TT) placement and monitor quality of CPR. Although the instantaneous end-tidal CO2 (EtCO2) value is of importance, additional information can also be obtained from the EtCO2 trend. Current defibrillator/monitors do not provide alerts based on EtCO2 trends. Objective To develop a defibrillator-based capnogram analysis program to provide sudden EtCO2 trend change alerts that can be used to alert rescuers to a variety of conditions. Methods Capnogram recordings from 154 OHCA patients were collected between 2008 & 2010 from two EMS agencies based in Oregon & Texas. De-identified clinical charts containing EMS self-reports were also obtained which contained time histories of events. The capnogram trend algorithm contains both rising and falling detectors and uses the difference between 30-second averages of EtCO2 from two adjacent sliding windows. The rising detector uses a threshold of a 50% increase and the falling detector uses a 30% decrease threshold to trigger. Results Sudden change alerts (N = 533) generated by the algorithm were correlated with events in the EMS charts or determined by examination of EtCO2, ECG, and compression waveforms. Sudden EtCO2 falling events were associated with poorer quality or stopped chest compression, hyperventilation, TT tube misplaced or dislodged, and loss of organized rhythm. Sudden EtCO2 rise events were associated with resumed or improved chest compression, successful airway placement, improved ventilation following hyperventilation, probable ROSC, and external pacing (n = 1). The remaining sudden change alerts were associated with artifacts in the capnogram waveform or could not be correlated. Conclusion An automated capnogram analysis program can accurately detect sudden trend changes in EtCO2 and help EMS personnel identify important events during OHCA resuscitation.
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