Autorelease Ensures Consistent Total PEEP With APRV

Abstract

Background:

A common method to maintain lung volume during the release period of APRV is to set Plow at 0 cm H₂O and titrate Tlow to create intrinsic PEEP. Tlow should be set to transition to Thigh when the expiratory flow is at 50-75% of PEF. A potential issue is that as airway mechanics change, total PEEP (PEEPtot) may also change. A possible solution is a feature on the Draeger Infinity V500, AutoRelease, which allows the user to set the percentage of PEF at which to transition to Phigh. The aim of this study was to determine whether AutoRelease maintains a more consistent PEEPtot when compared to a fixed Tlow in the context of changing lung compliance.

Methods:

A V500 ventilator was attached to an ASL Breathing Simulator. The ASL was set to: inspiratory resistance 5 cm H₂O/L/s, expiratory resistance 10 cm H₂O/L/s, and a passive model (Pmusc 0 cm H₂O). Compliance settings were 10 (C10), 30 (C30), and 50 (C50) mL/cm H₂O. Ventilator was set to: Phigh 30 cm H₂O, Plow 0 cm H₂O, Thigh 4 s, and Slope 0.2 s. For the AutoRelease (AR) group, AutoRelease was set to 75% of PEF. The set Tlow (TL) group, the Tlow was set to 0.38 s, which was associated with 75% of PEF at C30 and a release rate of 14 breaths/min. For both groups, PEEPtot and release volume were measured from the ventilator nine times at each compliance level, allowing 60 s to pass between measurements. Data was summarized in SPSS.

Results:

Mean +SD PEEPtot (cm H₂O) for TL vs AR at C10: 3.5 ± 0.1 vs 11.2 ± 0.2, P< 0.01; C30: 14. 7 ± 0.1 vs 14.0 ± 0.2, P< 0.01; and C50: 19.4 ± 0.1 vs 15.3 ± 0.1, P< 0.01. The release rate for AR ranged from 13.2 breaths/min at C50 to 14.4 breaths/min at C10. Release volumes increased as compliance increased. Mean release volumes (mL) for TL vs AR at C10 mL/cm H₂O: 366 vs 277; C30: 542 vs 542; and C50: 613 vs 789.

Conclusions:

A more consistent PEEPtot is maintained during APRV with AutoRelease compared to a set Tlow in the setting of changing compliance. PEEPtot for AR and TL was statistically significant at all three compliances, but at a compliance of 30 the PEEPtot is essentially the same by design. Release rate variation may have influence on results when a Thigh/Tlow ratio or release rate is ordered. Release volume variation is expected as compliance and PEEPtot change. A clinical trial should be conducted to determine whether these results are clinically important.

Disclosures:

None.