Tidal volume measurements via transthoracic impedance waveform characteristics: The effect of age, body mass index and gender. A single centre interventional study

• Published in: Resuscitation 2021-10, Vol.167, p.218-224
• Main Authors: Berve, P.O., Irusta, U., Kramer-Johansen, J., Skålhegg, T., Aramendi, E., Wik, L.
• Format: Article
• Language: English
• Subjects: CPR; Peak inspiration pressure; Pulmonary barotrauma; Pulmonary injury; Transthoracic impedance; Ventilation; Ventilation pattern
• ISSN: 0300-9572; 1873-1570
• DOI: 10.1016/j.resuscitation.2021.08.041

Measuring tidal volumes (TV) during bag-valve ventilation is challenging in the clinical setting. The ventilation waveform amplitude of the transthoracic impedance (TTI-amplitude) correlates well with TV for an individual, but poorer between patients. We hypothesized that TV to TTI-amplitude relations could be improved when adjusted for morphometric variables like body mass index (BMI), gender or age, and that TTI-amplitude cut-offs for ventilations with adequate TV (>400ml) could be established. Twenty-one consenting adults (9 female, and 9 overall overweight) during positive pressure ventilation in anaesthesia before scheduled surgery were included. Seventeen ventilator modes were used (⩾ five breaths per mode) to adjust different TVs (150–800 ml), ventilation frequencies (10–30 min−1) and insufflation times (0.5–3.5 s). TTI from the defibrillation pads was filtered to obtain ventilation TTI-amplitudes. Linear regression models were fitted between target and explanatory variables, and compared (coefficient of determination, R2). The TV to TTI-amplitude slope was 1.39 Ω/l (R2=0.52), with significant differences (p