Tracheal gas insufflation - Limits of efficacy in adults with acute respiratory distress syndrome

In mechanically ventilated adults with acute respiratory distress syndrome (ARDS), peak airway pressures (Paw(peak)) above 35 cm H2O may increase the risk of barotrauma or volutrauma. Tracheal gas insufflation (TGI), an adjun ctive ventilatory technique, may facilitate a reduction in set inspiratory pressure in these patients, and thereby in the tidal volume (VT) and Paw(pe ak) used in their ventilation, without a consequent increase in arterial ca rbon dioxide tension (Pa-co2). The purpose of this study was to: (I) assess the limits of efficacy of continuous TGI at two levels of decreased mechan ical ventilatory support; and (2) determine an appropriate time interval af ter initiation of TGI at which to evaluate response. We prospectively studi ed eight adults with ARDS and increased airway pressures (40.2 +/- 2.7 cm H 2O) who were managed with pressure-control ventilation (PCV). After obtaini ng baseline ventilatory and hemodynamic measures, we initiated TGI at 10 L/ min, adjusting ventilator positive-end expiratory pressure (PEEP) to mainta in baseline VT, and decreased the set inspiratory pressure by 5 cm H2O. Dat a were obtained after 30 and 60 min. Set inspiratory pressure was then decr eased by an additional 5 cm H2O (total: 10 cm H2O), and data were again obt ained after 30 min. Baseline (zero TGI) measures were then again recorded. Thirty minutes after decreasing the set inspiratory pressure by 5 cm H2O wi th TGI at 10 L/min, there was a 15% decrease in Paw(peak) and a 16% decreas e in VT as compared with their baseline values. However, Pa-co2 remained co nstant (59 +/- 10 mm Hg versus 57 +/- 6 mm Hg) (p = NS). There was no chang e in Pao, or in hemodynamic variables, and no differences between variables , at 30 min versus 60 min in seven subjects. The remaining subject did not tolerate the reduction in set inspiratory pressure for 60 min. Thirty minut es after the set inspiratory pressure was decreased by 10 cm H2O with TGI a t 10 L/min, there was a 26% decrease in Paw(peak) and a 26% decrease in VT. However, Pa-co2 increased by 19% and Pa-co2 decreased by 13%. Six subjects completed this phase of the protocol for 30 min, and one subject completed it for 60 min. TGI can be used to rapidly facilitate a 5 cm H2O reduction in set inspiratory pressure without an increase in Pa-co2. The ability to a chieve a 5 cm H2O reduction in set inspiratory pressure without adverse phy siologic effects was evident within 30 min. Attempts to further reduce set inspiratory pressure were not successful.