Relationship between oscillatory volume and oscillatory pressure in neonatal high-frequency oscillatory ventilators: an in vitro study.

Objective: We analysed the relationship between oscillatory volume (V) and pressure amplitude (ΔP) in six neonatal high-frequency oscillatory (HFO) ventilators and related it to (1) the accuracy of V and ΔP measurements and (2) the maximal delivered ΔP.

Design: In vitro study.

Setting: Neonatal intensive care unit.

Interventions: Ventilators tested were VN800 (Dräger), Servo-n (Maquet Getinge), SensorMedics 3100A (Vyaire Medical), Fabian HFOi (Vyaire Medical), SLE6000 (SLE UK) and Humming Vue (Metran). We changed various settings and mechanical characteristics of the test lung to mimic preterm and term conditions.

Main Outcome Measures: For each condition, we measured V and ΔP. We assessed the accuracy of the V and ΔP measurements versus a reference measurement system using linear regression and Bland-Altman analysis. We evaluated the maximum delivered ΔP at different oscillatory frequencies.

Results: We observed large variability between machines in the ΔP displayed at any target V. Most ventilators over-read ΔP with errors up to 30 cmHO or 60%. The error in the measurement of V was up to ±2 mL or ±30%. We observed high variability in the accuracy of ΔP and V measurements; the SLE6000 committed the lowest errors in ΔP measurements and the Fabian HFOi in V. The maximum delivered ΔP varied depending on the ventilator, being maximal for the Humming Vue, followed by the SLE6000 and SensorMedics 3100A.

Conclusions: The variability in the relationship between V and ΔP among HFO ventilators is largely explained by the variable accuracy in ΔP and V measurement. Different ventilators also exhibit important differences in the maximal generated ΔP.