Effect of PEEP-valve placement on function of a home-care ventilator

The addition of a PEEP valve to the circuit of a home-care ventilator like the Aequitron LP-6 can be viewed as a consumer modification of the system. We sought to determine the effect that such a modification would have on ventilator function.

Part 1. We tested the effect of PEEP level and PEEP-valve position on volume delivered at the ventilator Y-adapter, over a range of tidal volumes. Part 2. We held tidal volume, frequency, and inspiratory time constant, and varied PEEP level and PEEP-valve position to test the effect of PEEP-valve position on pressures measured at the ventilator outlet, patient-Y, and within the exhalation-valve pressurization line.

Conventional placement of the PEEP value (distal to, or 'after,' the exhalation valve) in the LP-6 ventilator circuit resulted in statistically significant and potentially clinically important decreases in the volumes delivered to the patient at some ventilator settings. Proximal placement of the PEEP valve (proximal to, or 'before,' the exhalation valve) resulted in consistent volumes delivered to the patient at all levels tested, without changing the ventilatory performance characteristics of the ventilator as reflected by pressure waveforms.

We recommend that appropriate observations and measurements be made to verify system function before a home-care ventilator modified to provide PEEP is applied to the patient.