Background and aim

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 ($>400\mathrm{ml}$) could be established.

Materials and methods

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, $R^2$).

Results

The TV to TTI-amplitude slope was 1.39 Ω/l ($R^2=0.52$), 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 ($R^2=0.66$) when BMI, age and gender were included.

Conclusions

TTI-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.

中文翻译：

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通过经胸阻抗波形特征测量潮气量：年龄、体重指数和性别的影响。单中心介入研究

背景与目标

在临床环境中，袋阀通气期间测量潮气量 (TV) 具有挑战性。经胸阻抗的通气波形幅度（TTI 幅度）与个体的 TV 相关性很好，但在患者之间较差。我们假设当调整身体质量指数 (BMI)、性别或年龄等形态测量变量时，TV 与 TTI 幅度的关系可以得到改善，并且 TTI 幅度临界值用于通气充足的 TV。$>400\mathrm{毫升}$) 可以成立。

材料和方法

21 名成人（9 名女性和 9 名总体超重）在计划手术前的麻醉正压通气期间被纳入。使用了十七种呼吸机模式（$⩾$每个模式五次呼吸）以调整不同的 TV（150–800 ml）、通气频率（10–30 min ^-1）和充气时间（0.5–3.5 s）。来自除颤垫的 TTI 被过滤以获得通气 TTI 振幅。在目标变量和解释变量之间拟合线性回归模型，并进行比较（决定系数、${\mathrm{电阻}}^2$）。

结果

TV 到 TTI 幅度斜率为 1.39 Ω/l (${\mathrm{电阻}}^2=0.52$), 有显着差异 ($磷<0.05$) 男性/女性 (1.04 Ω/l vs 1.84 Ω/l) 和正常/超重受试者 (1.65 Ω/l vs 1.04 Ω/l)。充足电视的中位数（四分位距）TTI 振幅截止值为 0.51 Ω(0.14–1.20)，男性和女性 (0.58 Ω/0.39 Ω)、正常和超重受试者 (0.52 Ω/0.46 Ω) 之间存在显着差异. 电视到 TTI 幅度模型改进（${\mathrm{电阻}}^2=0.66$) 当包括 BMI、年龄和性别时。

结论

建立了 TTI 振幅与 TV 的关系，并确定了具有足够 TV 的通气的截止值。与性别、年龄和 BMI 相关的患者形态测量变量解释了测量中的部分变异性。