Assessment of high-frequency neonatal ventilator performances

Abstract

We found that under our test conditions two of the three ventilators delivered adequate tidal volumes at the usual frequency of 15 Hz, regardless of the size of the endotracheal tube and of the mechanical properties of the respiratory system. When lung compliance increased or mean airway pressure decreased, both of which are common events during the recovery phase of hyaline membrane disease, we found that the intrinsic properties of two of the ventilators tested were responsible for a decrease in tidal volume. This decrease may account for some cases of heretofore unexplained hypercapnia.

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

“…As shown previously, [6][7][8]14 the principal factors influencing the mechanical performance of HFOV ventilators are frequency, inspiratory time, and load charge. Although all ventilators delivered lower V T with increasing frequencies, there were marked differences in the extent of V T decrease between ventilators at an oscillatory frequency of 15 Hz.…”

“…On the other hand, the Babylog VN500 presented important oscillatory flow limitations at high frequency settings as has also been reported in a recent bench study by John et al, 9 and these were similar to those seen in the older Babylog 8000. 6,7 This feature may be explained by the specific design of the Babylog VN500 that incorporates some of the technical concepts of the Babylog 8000 (ie, a Venturi multi-valve system on the expiratory side) combined with a new pulsed inspiratory flow. Because the flow is set automatically based on the frequency and the P aw , an insufficient bias flow may explain the power limitation of this ventilator seen in our study.…”

“…6,8,23 First, we used a test lung with airway resistance simulated using different sized airway resistors. This system allowed us to test different changes in respiratory mechanics but cannot completely reproduce the complexity of the neonatal respiratory system.…”

“…5 The technical features added to these new ventilators, in particular the choice of the ventilator mode between conventional mechanical ventilation and HFOV, the measurements of V T , and the volume-targeted mode during HFOV might represent all attractive features for the clinician, but data on volume delivery accuracy and performance of these new generation HFOV devices are lacking. Most of the published data on mechanical performance of oscillatory ventilators dates back more than 10 y, [6][7][8] and there is only one recent study, which looked into the performance of the Babylog VN500, showing a reduction of its power for generating oscillatory pressure amplitudes at higher operating frequencies. 9 Furthermore, published data on stability of V T during volume-targeted ventilation are conflicting.…”

Oscillatory Ventilator Performance: What Does It Mean?

“…no heat loss) that exist at frequencies above 5 Hz in a sealed glass flask. The adiabatic approach used in several previous assessments of oscillatory performance has the added advantage of removing the need for the insertion of an additional flowmeter into the circuit, and can be used to assess tidal volume delivery under heated and humidified conditions [3,5,6]. Furthermore, by varying the volume of the flask permit measurements across the range of compliances observed during moderately severe neonatal RDS, this approach arguably provides more accurate in vitro assessments of volume delivery, and its use should be strongly considered for future evaluations of oscillatory ventilator performance.…”