Proportional assist versus pressure support ventilation in patients with acute respiratory failure: Cardiorespiratory responses to artificially increased ventilatory demand*

Abstract

In patients with acute respiratory failure, dynamic inspiratory pressure assistance modalities are not superior to PSV with respect to cardiorespiratory function and inspiratory muscles unloading after increasing ventilatory demand. The latter might be explained by higher peak flows resulting in nonlinearly increased resistive workload that was incompletely compensated by PAV+ATC.

Tracheal pressure regulated volume assist ventilation in acute respiratory failure

“…This has been previously noted with conventional PAV (i.e., VAV+FAV) and attributed to mechanical unloading and improved neuromechanical coupling. 2,5,12,21 The influence of tube compensation, particularly as applied here using Ptr to regulate ventilator applied pressure, on breathing pattern variability has not been examined previously. These data are in contrast to other conventional modes of partial ventilatory support, particularly pressure support ventilation, where the manner in which positive pressure is applied limits the amount of variability observed.…”

“…4,5,12,21,[27][28][29][30] Navalesi and coworkers specifically characterized the consequences of increasing levels of VAV on total work of breathing over a wide range of support. 3 The reduction in elastic work achieved with VAV was offset in part by an increase in resistive work so that the decrease in total work of breathing was less than expected.…”

“…7,10 Failure to take this into account during FAV may lead to under-assistance as well as over-assistance, resulting in patient-ventilator asynchrony, frequent alarms, and increased caregiver intervention. 1,2,5,11,12 Clinical acceptance of PAV has been disappointing as a result of such considerations. 13,14 Automatic tube compensation (ATC) is a ventilatory modality designed to overcome the added flow resistance of an artificial airway by applying positive pressure in relationship to flow based on in vitro determination of tube resistance and continuous measurement of inspiratory flow and airway opening pressure (Pao) during pressure preset modes of ventilation.…”

Enhancing ventilatory strategies for the critically ill — proportional assist ventilation

“…Parce que la résistance des tubes trachéaux (Ret) varie considérablement selon le débit, la PAV (dont le principe de fonctionnement nécessite une résistance constante) ne compensera par correctement la Ret. [5][6][7] Une façon d'éliminer la charge résistive du tube trachéal est d'utiliser des modes tels que la compensation de tube automatique (automatic tube compensation), qui calcule la pression inspiratoire requise afin de compenser la résistance du tube trachéal à chaque respiration. Toutefois, ces systèmes ont des limites et ne fonctionnent pas toujours tel qu'attendu, fournissant alors une compensation sous-optimale à la résistance du tube endotrachéal.…”

“…Because resistance of tracheal tubes (Ret) varies significantly with flow, PAV (whose working principle requires a constant resistance) will poorly compensate for Ret. [5][6][7] One way to accommodate the tracheal tube resistive load is to use modes such as the automated tube compensation, which computes the ventilator pressure required to compensate for the resistance of the tracheal tube for every breath. However, there are limitations with these systems which do not always perform as expected, yielding suboptimal compensation of the endotracheal tube resistance.…”