Abstract Body: Background: End-Tidal Capnography (EtCO₂) is the primary ventilation bio-signal in out-of-hospital cardiac arrest (OHCA). Transthoracic Impedance (TTI) is a novel prehospital ventilation bio-signal. However, the variation in the quality of ventilation bio-signals remains poorly defined. We sought to compare the availability and quality of EtCO₂ and TTI during OHCA.
Methods: Retrospective study of adult (≥18 years) OHCA in Columbus, OH. We sampled the first 100 OHCAs from April 1^st 2019 through December 31^st 2020. Bio-signals were recorded using either Zoll or Lifepak defibrillator monitors. We included cases with ≥ 3 minutes of both bio-signals recorded. Using previously validated automated signal processing algorithms, we identified EtCO₂ and TTI ventilations. We manually classified EtCO₂ quality (low, medium, or high) based on the availability of the 4 phases (upstroke, plateau, downstroke and inspiratory pauses). We developed an automated TTI quality (low, medium, or high) algorithm based on a threshold balancing percentage of dependable impedance and ventilation rate error. We defined reliable ventilations as instances with: EtCO₂ = medium or high quality; or TTI = high quality. We determined the mean minutes with standard deviations in each quality level. Per case, we calculated the percentage of resuscitation time in each of the quality levels over resuscitation.
Results: Of the 100 cases, 87 cases (44 Zoll, 43 Lifepak) were included. The average resuscitation duration was 20.10±10.09min. Ventilations per minute (vpm) detection errors were minimal (EtCO₂: 0.4±0.5vpm; TTI: 1.0±1.1vpm). When using EtCO₂ alone, we reliably detected ventilations for 6.3±6.8min (30.2±28.0%). When using TTI alone, we reliably detected ventilations for 1.7±2.9min (8.4±15.0%). When using both bios-signals, we reliably detected ventilations for 3.9±5.2 min (18.4±24.7%). Both ventilation bio-signals were unreliable for 7.8±5.9min (40.5±28.3%) and not recorded for 0.5±1.4min (2.4±6.0%). Ventilation quality distributions per case are displayed in Figure 1.
Conclusions: When using EtCO₂, we reliably detect ventilation for greater periods of resuscitation than TTI. However, TTI detected ventilations can expand the period of ventilation evaluation. Utilization of both ventilation bio-signals can provide the broadest ventilation evaluation per resuscitation.