Expiratory phase and volume-adjusted tracheal gas insufflation: A lung model study

Objective: To evaluate in a lung model the effects of expiratory-phase tracheal gas insufflation (expiratory-phase TGI) with both volume and pressure control ventilation, and tidal volume adjusted continuous flow TGI (volume adjusted TGI) on system pressures and volumes. Design: Single-compartment lung model, Setting: Research laboratory in a university medical center. Interventions: Expiratory-phase TGI was established, using a solenoid valve activated by the ventilator, Volume adjusted TGI was applied by reducing tidal volume (VT) by the product of TGI flow and inspiratory time. Ventilation was provided with pressure control of 20 cm H2O or volume control ventilation with VT similar to that with pressure control ventilation. A rate of 15 breaths/min and positive end expiratory pressure (PEEP) of 10 cm H2O were used throughout, Inspiratory time periods of 1.0, 1.5, 2.0, and 2.5 sees were used with TGI flows of 0, 4, 8, and 12 L/min, Lung model compliance (mL/cm H2O) and resistance (cm H2O/L/sec) combinations of 20/20, 20/5, and 50/20 were used. Measurements and Main Results: In expiratory-phase TGI with pressure control ventilation, peak alveolar pressure remained constant, PEEP increased (p < .01) and VT decreased (p < .01), In expiratory-phase TGI with volume control ventilation and volume-adjusted TGI, there were significant increases in peak alveolar pressure and PEEP (p < .01), Readjustment of VT in volume-adjusted TGI was impassible with longer inspiratory time (greater than or equal to 2 sees) and higher TGI flows (greater than or equal to 8 L/min), Conclusions: The marked increases in system pressures and volumes observed with continuous-flow TGI can be avoided with expiratory-phase TGI and volume adjusted TGI.