Am. J. Respir. Crit. Care Med.,
Volume 162, Number 2, August 2000, 387-392
Tracheal Gas Insufflation
Limits of Efficacy in Adults with Acute Respiratory Distress Syndrome
LESLIE A.
HOFFMAN,
ADELAIDA M.
MIRO,
FREDERICK J.
TASOTA,
EDGAR
DELGADO,
THOMAS G.
ZULLO,
JOHN
LUTZ,
and
MICHAEL R.
PINSKY
Department of Acute/Tertiary Care, School of Nursing; Department of Anesthesiology and Critical Care Medicine, School of Medicine, University of
Pittsburgh; and Respiratory Care Department, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania
In mechanically ventilated adults with acute respiratory distress
syndrome (ARDS), peak airway pressures (Pawpeak) above 35 cm
H2O may increase the risk of barotrauma or volutrauma. Tracheal gas insufflation (TGI), an adjunctive ventilatory technique, may facilitate a reduction in set inspiratory pressure in these patients, and thereby in the tidal volume (VT) and Pawpeak used in their ventilation, without a consequent increase in arterial carbon dioxide
tension (PaCO2). The purpose of this study was to: (1) assess the
limits of efficacy of continuous TGI at two levels of decreased mechanical ventilatory support; and (2) determine an appropriate
time interval after initiation of TGI at which to evaluate response.
We prospectively studied eight adults with ARDS and increased
airway pressures (40.2 ± 2.7 cm H2O) who were managed with
pressure-control ventilation (PCV). After obtaining baseline ventilatory and hemodynamic measures, we initiated TGI at 10 L/min,
adjusting ventilator positive-end expiratory pressure (PEEP) to
maintain baseline VT, and decreased the set inspiratory pressure
by 5 cm H2O. Data were obtained after 30 and 60 min. Set inspiratory pressure was then decreased by an additional 5 cm H2O (total: 10 cm H2O), and data were again obtained after 30 min. Baseline (zero TGI) measures were then again recorded. Thirty minutes
after decreasing the set inspiratory pressure by 5 cm H2O with TGI
at 10 L/min, there was a 15% decrease in Pawpeak and a 16% decrease in VT as compared with their baseline values. However,
PaCO2 remained constant (59 ± 10 mm Hg versus 57 ± 6 mm Hg)
(p = NS). There was no change in PaO2 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 minutes after the set inspiratory pressure was decreased by 10 cm H2O with
TGI at 10 L/min, there was a 26% decrease in Pawpeak and a 26%
decrease in VT. However, PaCO2 increased by 19% and PaO2 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 PaCO2. The ability to achieve a 5 cm
H2O reduction in set inspiratory pressure without adverse physiologic effects was evident within 30 min. Attempts to further reduce set inspiratory pressure were not successful.
