Defining thoracic impedance thresholds for rescue ventilation: a laboratory study

To establish evidence-based peak amplitude thresholds for thoracic bioimpedance monitoring of ventilation and characterize the relationship between peak amplitude and tidal volume across two defibrillator devices used in pre-hospital care during cardiopulmonary resuscitation.

Thirty healthy adults underwent mechanical ventilation while thoracic bioimpedance was monitored using LifePak12 and HeartStart MRx defibrillators at five tidal volumes (250-800 mL). Peak amplitude measurements were extracted from thoracic bioimpedance waveforms. Linear mixed-effects models accounted for repeated measurements. Sex-stratified analyses examined device-specific sensitivity differences. Breath detection thresholds were calculated at various target sensitivities.

Linear relationships were observed for both devices. The LifePak 12 device showed tidal volume slopes of 0.0022 Ω/mL for females and 0.0013 Ω/mL for males. The HeartStart MRx device demonstrated slopes of 0.0030 Ω/mL for females and 0.0016 Ω/mL for males. Males showed 41-47% lower sensitivity to tidal volume changes than females across both devices. Model performance showed intraclass-correlations of 0.713-0.783 with prediction correlations exceeding 0.97. For the 250 mL breath, peak amplitude thresholds were 0.630/0.40 Ω (female/male) for LifePak12 and 0.45/0.30 Ω for HeartStart MRx at 90% detection sensitivity.

This study provides preliminary sex- and device-specific peak amplitude thresholds for breath identification using thoracic bioimpedance waveforms. The observed linear relationships and provided thresholds may improve categorical breath detection in resuscitation research. These findings require validation in cardiac arrest patients to ensure generalizability for clinical application.