Does change in thoracic impedance measured via defibrillator electrode pads accurately detect ventilation breaths in children?

INTRODUCTION: Resuscitation guidelines recommend rescue ventilations consist of tidal volumes 7-10 ml/kg. Changes in thoracic impedance (ΔTI) measured using defibrillator electrode pads to detect and guide rescue ventilations have not been studied in children. AIM: We hypothesized that ΔTI measured via standard anterior-apical (AA) position can accurately detect ventilations with volume > 7 ml/kg in children. We also compared standard AA position with alternative anterior-posterior (AP) position.
METHODS: IRB-approved, prospective, observational study of sedated, subjects (6 months to 17 years) on conventional mechanical ventilation. Thoracic impedance (TI) was obtained via Philips MRx defibrillator with standard electrode pads for 5 min each in AA and AP positions. Ventilations were simultaneously measured by pneumotachometer (Novametrix CO(2)SMO Plus).
RESULTS: Twenty-eight subjects (median 4 years, IQR 1.7-9 years; median 16.3 kg, IQR 10.5-39 kg) were enrolled. Data were available for 21 episodes in AA position and 22 episodes in AP position, with paired AA and AP data available for 18. For ventilations with volume < 7 ml/kg, the defibrillator algorithm detected 80.0% for both AA and AP (p=0.99). For ventilations ≥ 7 ml/kg, detection was 95.1% for AA and 95.7% for AP (p=0.38).
CONCLUSIONS: Changes in thoracic impedance obtained via defibrillator pads can accurately detect ventilations above 7 ml/kg in stable, mechanically ventilated children, corresponding to rescue ventilations recommended during CPR. Both AA and AP pad positions were less sensitive to detect smaller volumes (< 7 ml/kg) than higher volumes (≥ 7 ml/kg), suggesting that shallow ventilations during CPR might be missed. There were no differences in impedance measurements between standard AA pad position and commonly used alternative AP pad position.