Transthoracic Impedance Measured with Defibrillator Pads—New Interpretations of Signal Change Induced by Ventilations

Abstract

Compressions during the insufflation phase of ventilations may cause severe pulmonary injury during cardiopulmonary resuscitation (CPR). Transthoracic impedance (TTI) could be used to evaluate how chest compressions are aligned with ventilations if the insufflation phase could be identified in the TTI waveform without chest compression artifacts. Therefore, the aim of this study was to determine whether and how the insufflation phase could be precisely identified during TTI. We synchronously measured TTI and airway pressure (Paw) in 21 consenting anaesthetised patients, TTI through the defibrillator pads and Paw by connecting the monitor-defibrillator’s pressure-line to the endotracheal tube filter. Volume control mode with seventeen different settings were used (5–10 ventilations/setting): Six volumes (150–800 mL) with 12 min−1 frequency, four frequencies (10, 12, 22 and 30 min−1) with 400 mL volume, and seven inspiratory times (0.5–3.5 s ) with 400 mL/10 min−1 volume/frequency. Median time differences (quartile range) between timing of expiration onset in the Paw-line (PawEO) and the TTI peak and TTI maximum downslope were measured. TTI peak and PawEO time difference was 579 (432–723) m s for 12 min−1, independent of volume, with a negative relation to frequency, and it increased linearly with inspiratory time (slope 0.47, R 2 = 0.72). PawEO and TTI maximum downslope time difference was between −69 and 84 m s for any ventilation setting (time aligned). It was independent ( R 2 < 0.01) of volume, frequency and inspiratory time, with global median values of −47 (−153–65) m s , −40 (−168–68) m s and 20 (−93–128) m s , for varying volume, frequency and inspiratory time, respectively. The TTI peak is not aligned with the start of exhalation, but the TTI maximum downslope is. This knowledge could help with identifying the ideal ventilation pattern during CPR.

A Systematic Review of the Transthoracic Impedance during Cardiac Defibrillation

“…In the study by Sirna et al a 9% lower mean TTI was observed during end-expiration compared to end-inspiration (50 ± 3 vs. 55 ± 3 ) [ 23 ]. In another study, the onset of expiration coincides with the maximum drop in the ventilation TTI curve [ 59 ]. These results were confirmed by Deakin et al, where higher lung volumes appear to result in longer current paths, leading to greater TTI [ 56 ].…”

Mechanical Ventilation Management During Mechanical Chest Compressions

“…The mechanisms through which this generates hemodynamic impairments have been clearly demonstrated in the literature. 27,37 Fitz-Clarke 28 highlighted the relationship between target V T and the duration of the inspiratory phase by means of a physiological model. The model showed that the length of the inspiratory phase correlates inversely with the pressure regime, such that an inspiratory time that was too short could result in gastric insufflation.…”

Study on the Improvement of Electrical Facility System of Automated External Defibrillators by Real-Time Measurement of Thoracic Impedance

“…We refer to a studies that measures the change of mechanical impedance of patients during CPR [24][25][26]. In order to investigate the relationship between CPR strength and periodic changes in bioelectrical impedance, CPR experiments were conducted on the experimental body made by applying different modulus of elasticity of springs in the human body model.…”