Pressure-release Tracheal Gas Insufflation Reduces Airway Pressures in Lung-injured Sheep Maintaining Eucapnia

Abstract

Although tracheal gas insufflation (TGI) has proved to be a useful adjunct to mechanical ventilation, end-inspiratory as well as end-expiratory pressures may increase. We investigated the ability of continuous-flow TGI to maintain eucapnia while reducing airway pressure (Paw) and tidal volume (VT). Seven sheep (36 +/- 2 kg) were ventilated using the Dräger Evita 4 in the pressure control plus mode where flow is released via the expiratory valve to maintain constant inspiratory pressure. To avoid TGI-generated positive end-expiratory pressure (PEEP), a prototype reverse flow TGI tube was used. Two TGI flows (5 and 10 L/min) were investigated pre- and postsaline lavage-induced lung injury. Inspiratory pressures and VT were significantly reduced as TGI flow increased. At 10 L/min TGI flow the carinal pressures (Pcar) and VT were reduced pre- and postinjury by 15% and 20%, and by 28% and 34%, respectively. Tidal volume to dead space ratio (VD/VT) decreased preinjury from 0.49 +/- 0.1 to 0.18 +/- 0.2 and postinjury from 0.62 +/- 0.1 to 0.33 +/- 0.1 at a TGI flow of 10 L/min. The combination of the reverse flow TGI tube and a ventilator with an inspiratory pressure relief mechanism kept set end-inspiratory and end-expiratory pressures constant. This TGI system effectively reduced set Paw and VT while maintaining eucapnia.

Dead-space reduction and tracheal pressure measurements using a coaxial inner tube in an endotracheal tube

“…On the other hand, reversed I:E ratio ventilation and large tidal volumes resulted in substantial PEEPi development; still, the DLT is not intended to be used with such ventilator settings. A major problem with the use of TGI is the lack of tracheal pressure monitoring and especially the occurrence of unobserved PEEPi [22]. In most studies on PEEPi and TGI, the PEEPi is attributed to the TGI flow, but it is worth emphasising that a high respiratory rate, the possibility of termination of expiratory TGI flow slightly after the start of inspiration [19], and the increase in expiratory resistance by the TGI catheter inserted through the endotracheal tube [23] can also contribute to the risk of development of unobserved PEEPi.…”

“…There was no further improvement by increasing the TGI flow above this level. Thus, TGI flows of 6-15 l/min used in a number of studies [13,17,19,22], are exaggerated and only add to excessive airway pressures. The DLT is as efficient in CO 2 washout as any mode of TGI, if the effect is limited to a reduction of instrumental dead-space.…”

“…At a CO 2 output level of 240 ml/min the CO 2 washout was also compared to tidal volume-adjusted continuous TGI and expiratory synchronised TGI. Precision of tracheal pressure monitoring and PEEPi formation during DLT ventilation was evaluated by comparing pressure in each limb above the tube to reference tracheal pressure, varying I:E ratios (1:2, 1:1, and 2:1), tidal volumes (300-700 ml), breathing frequencies (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25), and compliance (20-50 ml/ cmH 2 O). DLT ventilation had the same efficacy in removing CO 2 as continuous and expiratory synchronised TGI, reducing single alveolar CO 2 concentration by 9-21% compared to normal ventilation.…”

Insuflação de gás traqueal como recurso terapêutico em ventilação mecânica invasiva: revisão sistemática

“…A TGI tem como objetivo minimizar o estresse pulmonar, melhorando as trocas gasosas e reduzindo o volume corrente ventilatório e a pressão. Também melhora o índice volume/minuto, ajudando assim a reduzir a lesão pulmonar induzida pelo ventilador sem a exigência de elevadas pressões ventilatórias, propiciando uma recuperação mais rápida e a eficácia do tratamento 2,[11][12][13] . Existem dois mecanismos principais responsáveis pela redução do CO 2 durante a aplicação da TGI: o proximal, no qual o gás fresco é introduzido próximo à carina, deslocando o gás contido no espaço morto anatômico proximal até a extremidade do cateter no final da expiração; e o distal, no qual a turbulência gerada pelo jato na extremidade do cateter pode elevar a mistura gasosa em regiões distais ao orifício, aumentando ainda mais a eliminação de CO 2 .…”

Application of Tracheal Gas Insufflation to Acute Unilateral Lung Injury in an Experimental Model

“…TGI can be used either to decrease Pa CO 2 in the setting of hypercapnia or to limit ventilatory distending forces by allowing a reduction in V T while maintaining constant Pa CO 2 (11)(12)(13)(14)(15). In severe unilateral lung injury, we hypothesized that selective application of TGI to the diseased lung ( 1 ) may increase lung volume of collapsed regions without adversely affecting blood flow or causing regional lung overdistension and ( 2 ) may allow a reduction in V T while maintaining eucapnia, thus decreasing the potential for VALI.…”