• J Clin Monit Comput · Oct 2022

    A comparison of endotracheal tube compensation techniques for the measurement of respiratory mechanical impedance at low frequencies.

    • Andrea F Cruz, Jacob Herrmann, CarvalhoCarlos R RCRR0000-0002-1618-8509Laboratorio de Pneumologia LIM-09, Disciplina de Pneumologia, Heart Institute (Incor), Hospital das Clinicas da Faculdade de Medicina da Universidade de São Paulo, São Paulo, São Paulo, Brazil., and David W Kaczka.
    • Laboratorio de Pneumologia LIM-09, Disciplina de Pneumologia, Heart Institute (Incor), Hospital das Clinicas da Faculdade de Medicina da Universidade de São Paulo, São Paulo, São Paulo, Brazil.
    • J Clin Monit Comput. 2022 Oct 1; 36 (5): 146114771461-1477.

    AbstractMeasurement of respiratory impedance ([Formula: see text]) in intubated patients requires accurate compensation for pressure losses across the endotracheal tube (ETT). In this study, we compared time-domain (TD), frequency-domain (FD) and combined time-/frequency-domain (FT) methods for ETT compensation. We measured total impedance ([Formula: see text]) of a test lung in series with three different ETT sizes, as well as in three intubated porcine subjects. Pressure measurement at the distal end of the ETT was used to determine the true [Formula: see text]. For TD compensation, pressure distal to the ETT was obtained based on its resistive and inertial properties, and the corresponding [Formula: see text] was estimated. For FD compensation, impedance of the isolated ETT was obtained from oscillatory flow and pressure waveforms, and then subtracted from [Formula: see text]. For TF compensation, the nonlinear resistive properties of the ETT were subtracted from the proximal pressure measurement, from which the linear resistive and inertial ETT properties were removed in the frequency-domain to obtain [Formula: see text]. The relative root mean square error between the actual and estimated [Formula: see text] ([Formula: see text]) showed that TD compensation yielded the least accurate estimates of [Formula: see text] for the in vitro experiments, with small deviations observed at higher frequencies. The FD and TF compensations yielded estimates of [Formula: see text] with similar accuracies. For the porcine subjects, no significant differences were observed in [Formula: see text] across compensation methods. FD and TF compensation of the ETT may allow for accurate oscillometric estimates of [Formula: see text] in intubated subjects, while avoiding the difficulties associated with direct tracheal pressure measurement.© 2021. The Author(s), under exclusive licence to Springer Nature B.V.

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