Impact of Plow on Flow,Tidal Volume,and Inspiratory PEEP in APRV

Abstract

Background:

In airway pressure release ventilation (APRV), there have been questions about whether increases in pressure low (Plow) will impact flow characteristics while maintaining a time low (Tlow) of 75%. We hypothesize that the addition of Plow will not change the flow characteristics.

Methods:

Utilizing the Hamilton G5 (Bonaduz, Switzerland) and Drager V500 (Lubeck, Germany) mechanical ventilators, we created a baseline with the following settings: High pressure (Phigh) 20 cm H₂O, low pressure (Plow) 0 cm H₂O, time high (Thigh) 6 s, time low (Tlow) 75% of peak expiratory flow (PEF). Intrinsic PEEP and the change in pressure from <Phigh to intrinsic PEEP (ΔP) were measured and the Phigh was adjusted with increases in set Plow to maintain the same ΔP. Plow was increased in increments of 5 cm H₂O up to 20 cm H₂O. The T-low was adjusted to as close to 75% of PEF as possible. A Thigh of 6 S, and ΔP of 12 cm H₂O was maintained for the Hamilton G5 and a ΔP of 11 cm H₂O for the Drager V500. The ASL 5000 was set to passive breathing, PEF, V_T, intrinsic PEEP and T-low were recorded every 5 breaths.

Results:

The addition of Plow resulted in a expiratory flow decrease of 12 L/min on both ventilators from a Plow of 0 to 20 cm H₂O. the tidal volumes increased by almost triple even while maintaining the same ΔP. Additionally, the increases in PEEP did not simply increase by the same number in Plow.

Conclusions:

With the addition of Plow, flow characteristics did change, the intrinsic PEEP increased by unpredictable values, and the V_T increased by almost triple despite maintaining the same ΔP. The addition of Plow does impact the flow, V_T, and intrinsic PEEP in patients and caution should be taken when applying it to APRV.