2005 OPEN FORUM Abstracts
IMPACT OF COMPLIANCE AND RESISTANCE VARIATION IN APRV: A TEST LUNG STUDY
Gordon Maniere RRT1, Gregory Naworol RRT1, Richard Castina RRT1, David Rice MD2, Catherine Shoff MD2, Thomas KelleyMD2, Patrick Allan MD2 Respiratory Therapy1 and Pulmonary/Critical Care Medicine2, Wilford Hall Medical Center, Lackland AFB, TX
BACKGROUND: Airway pressure release ventilation (APRV) may, relative to other modes of conventional ventilation, offer hemodynamic and oxygenation benefits to acute respiratory distress syndrome patients (ARDS). It is uncertain what impact APRV, at a broad range of inspiratory:expiratory time (I:E) ratios and high and low pressures (Phigh and PEEP, respectively), will have upon tidal volume (Tv). We evaluated the impact of altering I:E and airway pressures on Tv utilizing APRV with a mechanical lung model.
METHODS: A Servo-I ventilator (Maquet, Solna, Sweden) was interfaced to a mechanical lung (Michigan Instruments 5600i) via an artificial trachea intubated with a 8.0 mm cuffed endotracheal tube (ETT). Validation of delivered Tv, airway pressure, and flow was accomplished with a respiratory monitor (Bicore CP100, Irvine, CA) inserted between the circuit wye and ETT. The Servo-I was set to Bi-Ventâ at Phigh range 10 - 36 cm H2O, Plow 0 cm H2O, Thigh 1-4.5 sec, Tlow 1-4.5 sec. Spontaneous breath triggering was not simulated with the mechanical lung. Triplicate trials were conducted using mechanical lung compliances of 90 ml/cm H2O and 30 ml/cm H2O to simulate high and low lung compliance conditions respectively, without the use of in-line resistors. Changes in tidal volume, flow, mean airway pressure, peak airway pressure, and auto-PEEP were measured with the ventilator and in-line Bicore CP 100.
RESULTS: The Tv changes with a fixed Phigh (36 cm H20) and varying Thigh (1-4.5s) (Figure1), and the Tv with a fixed Thigh (4s) and a varying Phigh (10-36cmH20) (Figure 2) are displayed. The data for both figures were collected at a 30 ml/cm H20 compliance.
CONCLUSION: The incremental change in Tv is attenuated at extremes of Thigh when examined in conjunction with a constant Phigh. Incremental changes in Tv are also attenuated with increases in Phigh with a fixed Thigh. These attenuated Tv changes are a consequence of auto-PEEP effects.