In vitroestimation of pressure drop across tracheal tubes during high-frequency percussive ventilation

Abstract

Tracheal tubes (TT) are used in clinical practice to connect an artificial ventilator to the patient's airways. It is important to know the pressure used to overcome tube impedance to avoid lung injury. Although high-frequency percussive ventilation (HFPV) has been increasingly used, the mechanical behavior of TT under HFPV has not yet been described. Thus, we aimed at characterizing in vitro the pressure drop across TT (ΔPTT) by identifying the model that best fits the measured pressure-flow (P-V̇) relationships during HFPV under different working pressures (PWork), percussive frequencies and mechanical loads. Three simple models relating ΔPTT and flow (V̇) were tested. Model 1 is characterized by linear resistive [Rtube ⋅ V̇(t)] and inertial [I · V̈(t)] terms. Model 2 takes into consideration Rohrer's approach [K1· V̇(t) + K2 ⋅V̇(t)] and inertance [I ·V̈(t)]. In model 3 the pressure drop caused by friction is represented by the non-linear Blasius component [Kb· V̇(1.75)(t)] and the inertial term [I· V̈(t)]. Model 1 presented a significantly higher root mean square error of approximation than models 2 and 3, which were similar. Thus, model 1 was not as accurate as the latter, possibly due to turbulence. Model 3 presented the most robust resistance-related coefficient. Estimated inertances did not vary among the models using the same tube. In conclusion, in HFPV ΔPTT can be easily calculated by the physician using model 3.

High frequency percussive ventilation increases alveolar recruitment in early acute respiratory distress syndrome: an experimental, physiological and CT scan study

“…This 30-cmH 2 0 pressure seems to limit the risk of distension-related lung injury as reported by Boussarsar [ 41 ] and Tobin [ 42 ]. A recent study elucidated pressure drops through endotracheal tubes [ 43 ]. During the mini-burst inspiratory phase, pressure drops were: 9.28 (4.95–12.93), 9.48 (5.05–13.47), and 10.04 (5.62–16.97) cmH 2 O for diameters 8, 7.5 and 6.5, respectively [ 44 ].…”

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

“…Data obtained with pseudorandom waveform integer multiple (IM), non-sum non-difference order 2 (NSND-2) and non-sum non-difference order 3 (NSND- The description of ETT pressure losses using Eq. 4 [26] incorporates nonlinear resistive and linear inertial characteristics, which are often used for ETT compensation during mechanical ventilation [22,40,41,49]. Moreover, many commercial mechanical ventilators provide automatic tube compensation (ATC) algorithms, based on the coefficients of this equation [50].…”

On some factors determining the pressure drop across tracheal tubes during high-frequency percussive ventilation: a flow-independent model

“…For these reason the estimation of tracheal tube contribution to airway peak pressure is of paramount importance to avoid damage to the lung during mechanical ventilation [3], as well as to adequately apply the lung ventilatory protective strategy [6][7][8] and avoid under-treatment. Several models have been proposed to estimate pressure drop across the tracheal tube during artificial ventilation [3,4,13,16]. However, all of them depend on flow measurement that is not present in high frequency percussive ventilators.…”

“…To overcome this limitation a portable instrument has been proposed to measure flow during HFPV but it cannot estimate ΔP TT [15]. Recently, a model to calculate ΔP TT based on flow and Blasius' constant has been described [16]. Even though it is very robust the flow measurement is mandatory, which may be difficult to perform in some clinical scenarios.…”