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

Abstract

Background: The mode of waveform generation and circuit characteristics differ between high-frequency oscillators. It is unknown if this influences performance. Objectives: To describe the relationships between set and delivered pressure amplitude (ΔP), and the interaction with frequency and endotracheal tube (ETT) diameter, in eight high-frequency oscillators. Methods: Oscillators were evaluated using a 70-ml test lung at 1.0 and 2.0 ml/cm H₂O compliance, with mean airway pressures (P_AW) of 10 and 20 cm H₂O, frequencies of 5, 10 and 15 Hz, and an ETT diameter of 2.5 and 3.5 mm. At each permutation of P_AW, frequency and ETT, the set ΔP was sequentially increased from 15 to 50 cm H₂O, or from 20 to 100% maximum amplitude (10% increments) depending on the oscillator design. The ΔP at the ventilator (ΔP_VENT), airway opening (ΔP_AO) and within the test lung (ΔP_TRACH), and tidal volume (V_T) at the airway opening were determined at each set ΔP. Results: In two oscillators the relationships between set and delivered ΔP were non-linear, with a plateau in ΔP thresholds noted at all frequencies (Dräger Babylog 8000) or ≥10 Hz (Dräger VN500). In all other devices there was a linear relationship between ΔP_VENT, ΔP_AO and ΔP_TRACH (all r² >0.93), with differing attenuation of the pressure wave. Delivered V_T at the different settings tested varied between devices, with some unable to deliver V_T >3 ml at 15 Hz, and others generating V_T >20 ml at 5 Hz and a 1:1 inspiratory-to-expiratory time ratio. Conclusions: Clinicians should be aware that modern high-frequency oscillators exhibit important differences in the delivered ΔP and V_T.

Non-invasive high-frequency oscillatory ventilation in neonates: review of physiology, biology and clinical data

“…Some other devices produce high-frequency oscillations by flow interruption due to the cyclic opening-closure of the end expiratory pressure valve and this cannot strictly be considered a form of NHFOV. Several modern neonatal ventilators are technically able to provide NHFOV, although their performance may be variable at extreme settings or for term neonates 8 9. A recent European survey described wide variation in the type of device used to provide NHFOV 5.…”

Oscillatory Ventilator Performance: What Does It Mean?

“…Consequently, if using more than one type of oscillator within the neonatal unit, it is inappropriate to simply transfer a patient from one device to the next using the same ventilator settings. Tingay et al [1] appropriately advise caution in extrapolating the results of their in vitro study to human patients under physiological conditions where tidal volumes higher (or lower) than those reported here may be generated. Whilst percentages may exaggerate differences between devices, the absolute tidal volume and its ability to adequately ventilate the infant at the chosen frequency without undue intrathoracic oscillatory pressure swings are the most clinically important variables.…”

“…In this edition of Neonatology , Tingay et al [1] present the latest investigation, evaluating eight of the current, commercially available oscillatory ventilators. Their observation that differences in performance exist between oscillators echoes the general conclusions of previous studies, and is not unexpected.…”

“…As Tingay et al [1] discuss, there are important differences in the approaches used for the assessment of oscillatory performance and consequent limitations to the interpretations. Ideally, a test setup for evaluation of performance characteristics should replicate clinical settings as closely as possible, including the presence or absence of a flowmeter, use of heated humidified gas and a test lung that reflects the mechanical characteristics of a newborn infant with respiratory distress.…”

“…Tingay et al [1] assessed most ventilators using inspiratory to expiratory time ratios ( t I :t E ) of 1:2, except where this option was not available (SLE 5000). The SM3100B was evaluated at both ratios of 1:1 and 1:2 to provide some comparative data of the effect of changing t I :t E .…”