The Science Journal of the American Association for Respiratory Care

2005 OPEN FORUM Abstracts

BI-vent Auto-Cycling Associated With Simulated air-leak In A Mechanical Lung Model

Gregory Naworol RRT1, Gordon Maniere RRT1, Richard Castina RRT1,David Rice MD2, Delano Fabro DO2, Michael Van de Kieft MD2, Patrick Allan MD2, Stephen Derdak DO2 Respiratory Therapy1 and Pulmonary/Critical Care Medicine2, Wilford Hall Medical Center, Lackland AFB, TX

BACKGROUND: Spontaneous breathing duringairway pressure release ventilation (APRV or Bi-Ventâ) is facilitated by concurrent use of automatic tube compensation (ATC) or pressure support ventilation (PSV) depending on the ventilator manufacturer. The purpose of this research was to determine whether PSV use or ATC during APRV results in ventilator auto-cycling during simulated air-leak using a mechanical lung model.

METHODS: A Servo-I ventilator (Maquet, Solna, Sweden) and Drager Evita-2 Dura ventilator (Drager Medical, Telford, PA) were sequentially 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 tidal volume, 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 20 - 30 cm H2O, Plow 0 cm H2O, Thigh 1-4 sec, Tlow 1-4 sec with concurrent flow-triggered or pressure-triggered PSV (5 - 15 cm H2O). PSV flow-triggering was varied between 1 ("difficult") and 10 ("easy"). The Evita-2 was set in APRV mode with identical pressure and cycle times using concurrent ATC set at 100% ETT compensation. Spontaneous breath triggering was not simulated with the mechanical lung. Air-leaks were created by opening ports on the artificial trachea. Triplicate trials were conducted with each ventilator using mechanical lung compliances of 90 ml/cm H2O and 20 ml/cm H2O to simulate high and low lung compliance conditions respectively. 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: Flow-triggering (set at 10,"easy") with PSV during Bi-Vent on the Servo-I led to immediate auto-cycling with a simulated air-leaks of 250 - 500 ml from the artificial trachea. Auto-cycling was not observed when flow triggering was set at 1 ("difficult") or when pressure-triggering was set. In contrast, ATC use on the Evita-2 ventilator did not demonstrate auto-cycling with any level of simulated air-leak. Complete or partial ETT cuff-deflation did not result in auto-cycling with either ventilator.

CONCLUSIONS: The presence of large volume air-leaks may cause ventilator auto-cycling during Bi-Ventâ when using flow-triggered PSV. Auto-cycling may be prevented by using pressure-triggered PSV during Bi-Vent. In contrast, ATC use during APRV does not result in auto-cycling with similar degrees of air-leak. The absence of demonstrable auto-cycling with ETT cuff-deflation may be secondary to the mechanical characteristics of the mechanical lung model used.

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BI-vent Auto-Cycling Associated With Simulated air-leak In A Mechanical Lung Model