Tracheal pressure regulated volume assist ventilation in acute respiratory failure

Abstract

Purpose: Proportional assist ventilation (PAV) uses volume assist (VAV) and flow assist ventilation (FAV) to reduce elastic and resistive effort, respectively. Proportional assist ventilation may be difficult to apply clinically, particularly due to FAV related considerations. It was hypothesized that regulating tracheal (Ptr) rather than airway opening pressure (Pao), to overcome endotracheal tube related resistive effort, during VAV would provide an effective alternative method of ventilation. We therefore compared the effects of Pao and Ptr regulated VAV on breathing pattern and inspiratory effort. Methods:In seven intubated patients, flow, volume, Pao, Ptr, esophageal and transdiaphragmatic pressure were measured during VAV (0-80% respiratory system elastance) using Pao vs Ptr to regulate ventilator applied pressure. Breathing pattern and the pressure-time integral of the inspiratory muscles (∫P mus ⋅dt) and diaphragm (∫P di ⋅dt) were determined.Results: Compared to spontaneous breathing, the respiratory rate to tidal volume ratio, or rapid shallow breathing index (RSBI), improved progressively with increasing VAV (130 ± 64 vs 70 ± 35, VAV 0 vs 80%; P < 0.05) while inspiratory effort fell (∫P mus ⋅dt = 39.6 ± 7.5 vs 28.5 ± 7.2 cm H 2 O·sec·L -1 , ∫P di ⋅dt, = 35.4 ± 7.8 vs 24.2 ± 5.9 cm H 2 O·sec·L -1 , VAV 0 vs 80%; P < 0.05) due to a decrease in elastic related effort. At any given level of support, there was further reduction in RSBI, ∫P mus ⋅dt, and ∫P di ⋅dt (which averaged 23.6 ± 2.7, 33.7 ± 4.4, and 38.5 ± 5.1%, respectively; P < 0.05) for Ptr compared to Pao regulated VAV due to a decrease in resistive effort. Conclusions:Tracheal pressure regulated VAV can be a simple and effective method of partial ventilatory support in acute respiratory failure. Further work will be needed to determine its efficacy and potential benefit relative to PAV and other modes of ventilation in routine clinical practice.

Enhancing ventilatory strategies for the critically ill — proportional assist ventilation

“…This is illustrated in Figure 1 of Mirkovic's paper: panel A showing the inspiratory effort (partitioned into its components) of a typical patient with airway opening pressure regulation (left) and with tracheal pressure regulation (right), panel B showing the ventilator assistance provided by VAV with the same two regulation systems. 9 Unsurprisingly, VAV progressively reduced the patients' elastic effort with increasing level of assistance. More interestingly, tracheal pressure regulated ventilation provided an important assistance against resistive loads compared with the conventional system (airway opening pressure regulation).…”

“…8 In a study reported in this issue of the Journal, Mirkovic et al address some of these issues with the implementation of PAV in the clinical setting, bringing two modifications to the conventional PAV system. 9 First, they used a simplified version of PAV, volume assist ventilation (VAV), providing assistance solely for the elastic component of the respiratory system impedance without any assistance for the resis- tive component. Secondly, they moved the site of airway pressure measurement from the Y-piece of the breathing circuit to the distal end of the tracheal tube.…”

“…abordent certains des problèmes associés à la mise en oeuvre de la PAV dans un contexte clinique, et apportent deux modifications au système de PAV conventionnel. 9 En premier lieu, ils utilisent une version simplifiée de PAV, la ventilation assistée proportionnelle au volume (VAV), fournissant une aide uniquement à la composante élastique de l'impédance du système respiratoire, sans aucune assistance à la composante résistive. Deuxièmement, les auteurs ont déplacé le site de mesure de la pression aérienne de la pièce en Y du circuit respiratoire à l'extrémité distale du tube trachéal.…”

“…Ceci est illustré dans la figure 1 de l'article de Mirkovic : le panneau A montre l'effort inspiratoire (réparti en ses composantes) d'un patient typique avec régulation de la ventilation par la pression du circuit respiratoire (gauche) et avec régulation par la pression trachéale (droite) ; le panneau B montre l'aide respiratoire fournie par la VAV avec les deux mêmes systèmes de régulation. 9 Comme on pouvait s'y attendre, la VAV a réduit de façon progressive l'effort élastique du patient avec l'augmentation séquentielle du niveau d'assistance. Ce qui est intéressant, c'est que la ventilation régulée par la pression trachéale a fourni une aide importante contre les charges résistives par rapport au système conventionnel (régulation par la pression du circuit).…”