• P O Berve, U Irusta, J Kramer-Johansen, T Skålhegg, E Aramendi, and L Wik.
• Norwegian National Advisory Unit for Prehospital Emergency Medicine (NAKOS), Oslo University Hospital - Ullevål and University of Oslo, Po Box 4956 Nydalen, N-0424 Oslo, Norway; Air Ambulance Department, Division of Prehospital Services, Oslo University Hospital, Oslo, Norway. Electronic address: poberve@gmail.com.
• Resuscitation. 2021 Oct 1; 167: 218-224.

Background And AimMeasuring 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.Materials And MethodsTwenty-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).ResultsThe TV to TTI-amplitude slope was 1.39 Ω/l (R2=0.52), with significant differences (p<0.05) between male/female (1.04 Ω/l vs 1.84 Ω/l) and normal/overweight subjects (1.65 Ω/l vs 1.04 Ω/l). The median (interquartile range) TTI-amplitude cut-off for adequate TV was 0.51 Ω(0.14-1.20) with significant differences between males and females (0.58 Ω/0.39 Ω), and normal and overweight subjects (0.52 Ω/0.46 Ω). The TV to TTI-amplitude model improved (R2=0.66) when BMI, age and gender were included.ConclusionsTTI-amplitude to TV relations were established and cut-offs for ventilations with adequate TV determined. Patient morphometric variables related to gender, age and BMI explain part of the variability in the measurements.Copyright © 2021 Elsevier B.V. All rights reserved.

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