The endotracheal tube biases the estimates of pulmonary recruitment and overdistension

Abstract

To assess the impact of the endotracheal tube (ETT) and of different flow waveforms on estimates of alveolar cyclic recruitment (CR) and overdistension (AO). Numerical simulation of the respiratory system plus ETT (inertance L plus a flow-dependent resistance, K (1) and K (2)), with the following non-linear equation of motion PAW(t)= ((K1 + K2 x/V(t)/) x V(t) + L x V(t)) + Rrs x V(t) + (E1 + E2 x V(t) x V(t) + P0 (PAW pressure at the airways opening, V volume), under volume-controlled mechanical ventilation. An index %E2 = 100 x (E2 x V(T))/(E1 + E2)x V(T)) can be calculated where %E(2) > 30% represents AO and %E(2) < 0% represents CR. Parameters were estimated by the least-squares method, either with the complete equation or suppressing L, K(2) or both. %E(2) is always underestimated (down to -152 percent points) with incomplete equations of motion. The estimation of %E (2) may be strongly biased in the presence of an ETT excluded from the estimation model.

The augmented RIC model of the human respiratory system

“…Note that these models of impedance are all based upon a time-correspondence between an imposed pressure (at the mouth) and the resulting response of air flow, which satisfies a linear ordinary differential equation. This is in contrast to respiratory system models of the pressure-flow relationship with respect to time that satisfy nonlinear ordinary differential equations, such as [10] and [29]. Moreover, these stimulus-response models are also fundamentally different from the structural types modeling air (and particle) flow through the respiratory system, e.g., using computational fluid dynamics [2].…”

Respiratory system dynamical mechanical properties: modeling in time and frequency domain

“…As a consequence, the inertance has not been considered in the measurement of respiratory mechanical properties in adults during conventional ventilation (Lanteri et al 1999). However, neglecting the inertive component has recently been questioned, especially in mechanically ventilated patients with endotracheal tube (EET) (Sullivan et al 1976;Lanteri et al 1999;Jandre et al 2008). Additionally, mechanical ventilation in infants usually requires high respiratory frequency as well as an artificial airway with a small inner diameter and length, which contributes even more to the necessity of taking into account inertial properties.…”

“…The most common application of this model occurs in patients under mechanical ventilation with an endotracheal tube (Sullivan et al 1976;Lanteri et al 1999). In fact, it seems that under such conditions, the impedance of the endotracheal tube may significantly contribute to the global pressure-flow behavior (Sullivan et al 1976;Jandre et al 2008). However, the nature of the apparent nonlinearity in resistive properties seems to be much more dependent on the breathing pattern and flow waveform .…”

“…In general, the volume-dependent elastance model seems to be quite independent of the respiratory resistance or inertive components (Lanteri et al 1999;Jandre et al 2008). However, a study with numerically simulated data suggests that the unmindfulness of the endotracheal tube mechanical properties may bias the identification of overdistension, especially during mechanical ventilation with pressure-controlled ventilation .…”

Automated mechanical ventilation: adapting decision making to different disease states

“…In its actual status of development the system incorporates a total of three independent controllers: (i) a first controller for automatically setting the respiratory rate in order to control the CO 2 excretion such as described in the present study, (ii) a second controller for setting the inspiratory oxygen fraction (FiO 2 ) to control oxygenation and (iii) a third controller for setting tidal volume (V t ) and positive end-expiratory pressure (PEEP) to control the transfer of mechanical energy between ventilator and lungs based on the analysis of respiratory mechanics considering the mechanics of the artificial airways such as the endotracheal tube [10]. Since the ventilatory parameters cannot be controlled independently, the output of these basic controllers is manipulated in the optimization unit before being transmitted to the ventilator [15].…”