New Generation Neonatal High Frequency Ventilators: Effect of Oscillatory Frequency and Working Principles on Performance

Abstract

Increasing the frequency proportionally decreased the V T for all the ventilators, although the magnitude of the decrease was highly variable between ventilators. At 15 Hz and a pressure amplitude of 60 cm H 2 O, the delivered V T ranged from 3.5 to 5.9 mL between devices while simulating pre-term infant conditions and from 2.6 to 6.3 mL while simulating term infant conditions. Activating the volume-targeted mode in the 3 machines that offer this mode allowed the V T to remain constant over the range of frequencies and with changes of lung mechanical properties, for pre-term infant settings only while targeting a V T of 1 mL. CONCLUSIONS: These new generation neonatal ventilators were able to deliver adequate V T under pre-term infant, but not term infant respiratory system conditions. The clinical relevance of these findings will need to be determined by further studies.

Are All Oscillators Created Equal? In vitro Performance Characteristics of Eight High-Frequency Oscillatory Ventilators

“…This was intentional as humidifiers vary between oscillators, humidification provides a variable that is difficult to standardise and the mechanical test lung is not designed to be humidified, potentially influencing the fidelity of the pressure and flow measurements. Apart from the recent report of Grazioli et al [13], in which a dry humidification chamber was left in situ, all previous in vitro reports of HFOV performance have not reported whether the chamber was present [8,10,19]. …”

“…The VN500 and BL8000 displayed less linearity between the set ΔP and measured amplitudes, with a plateau at higher frequencies. This has been previously described for the BL8000 [8,9,10] and VN500 [13,14], and likely reflects similar design. Clinicians should be aware that these devices might perform differently at frequencies >10 Hz, requiring a lower frequency than the SM3100A and B, fabian HFO, SLE5000, Sophie, and Leoni Plus to achieve similar ΔP TRACH and, potentially, CO 2 clearance in some settings.…”

“…Although similar recent reports have also used the Michigan test lung [12,13,14,19], an alternative rigid test lung model was used in earlier in vitro assessments [8,10]. This model permits the use of the adiabatic gas equation to derive flow and volume and has potential advantages, including allowing humidification, permitting lower C L values and obviating the need for an additional flow sensor with its inherent influence on resistance.…”

“…In vitro test lungs do not have the same viscoelastic properties as a diseased human or animal lung, particularly hysteresis, which explains the lack of difference at the two P AW settings. For this reason, we did not evaluate the new ‘volume guarantee' modes offered by some manufacturers [13]. The theoretical advantage of ‘volume guarantee' is to rapidly modulate ΔP to changes in lung mechanics.…”

“…A new generation of high-frequency oscillators are now available and are all licenced for paediatric use. These are all hybrid devices with new methods of high-frequency pressure and flow waveform generation [12], and potential differences in V T delivery [13]. There are no reports to guide clinicians in the specific application of frequency and ΔP for each of these ventilators, and it is not known if the principles developed and validated in older devices are still applicable.…”