Abstract
Background:
Airway pressure release ventilation (APRV) is a pressure controlled mode of ventilation that ventilates the patient with a long Time High (Thigh) and short Time Low (Tlow) to intentionally create auto-PEEP. APRV may improve oxygenation and increase alveolar lung recruitment. The purpose of this bench study was to evaluate APRV on the Carefusion Avea (Avea) in APRV/BiLevel, Drager V500 (V500) in PC-APRV, Medtronics PB 980 (PB 980) in BiLevel, and Maquet Servo-I (Servo-i) in BiVent using the IngMar Medical ASL 5000 (ASL) electronic lung simulator set at three levels of static compliance (Cst) to simulate three severities of ARDS.
Methods:
An extended self-test was performed on each ventilator using oxygen and air. ASL settings: Cst 40 mL/cm H2O (mild), 30 mL/cm H2O (moderate), and 20 mL/cm H2O (severe); inspiratory resistance 12 cm H2O/L/s, expiratory resistance 14 cm H2O/L/s, and Pmus 0 cm H2O (apneic). The ASL was connected directly to the ventilator y-piece with a 22 mm adapter. Ventilator settings: Pressure High (Phigh) 17 and 22 cm H2O, Thigh 6 seconds, Pressure Low (Plow) 0 cm H2O, Tlow was adjusted to achieve a release point at 75% of Peak Expiratory Flow Rate (PEFR), Pressure Support 0 cm H2O, and Tube Compensation off. PEFR was measured directly from the ventilator flow waveforms. The ASL was ventilated for one minute to stabilize and one minute for data collection, first ventilating at Phigh 17 then 22 cm H2O. Data were recorded directly by the ASL and the parameters evaluated include: PEFR, peak inspiratory pressure (Ppeak), mean airway pressure (Pmean), total PEEP (PEEPtot), and expiratory tidal volume (exp VT).
Results:
Phigh 22 cm H2O resulted in an increase of all evaluated parameters. As Cst decreased, exp VT decreased. In severe ARDS, the Avea and the V500 exhibited the greatest exp VT . In severe ARDS the V500 and the Servo-I exhibited the greatest PEFR. Overall pressures (Ppeak and Pmean) were highest on the Avea. The Avea exhibited the highest level of PEEPtot while the V500 exhibited the lowest.
Conclusions:
This study demonstrated that all ventilators provided an increase in PEEPtot, exp VT, Pmean, PEFR, and Ppeak at Phigh of 22 cm H2O. The ventilators provided a different level of PEFR and PEEPtot at 75% PEFR. Further research is needed to compare APRV in patients to determine the amount of Auto-PEEP remaining in the lung at 75% PEFR in order to prevent derecruitment of the lung.
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