MECHANICAL PERFORMANCE OF CLINICALLY AVAILABLE, NEONATAL, HIGH-FREQUENCY, OSCILLATORY-TYPE VENTILATORS

Objective: To perform a functional evaluation of five different high f requency, oscillatory-type ventilators that are currently being market ed for neonatal high-frequency oscillation, Design: Observational anim al study, Setting: Laboratory, Subjects: New Zealand White male rabbit s, Interventions: Oscillator waveforms and delivered volumes were meas ured plethysmographically for the following ventilators: the SensorMed ics 3100 A; the Drager Baby Log 8000; the Metran Humming V; the Infant Star; and the Infant Star 950, The independent variables which were a djusted included frequency (5 to 15 Hz), amplitude (25% to 100%), mean airway pressure (5 to 25 cm H2O) and lung injury, Measurements and Ma in Results: At 15 Hz, the volume delivered at the 100% amplitude setti ng varied from 2.1 to 8.8 mL. Generally, the delivered volume decrease d with increasing frequency, and with increased percentage of amplitud e. Volume de livery was relatively unaffected by mean airway pressure but decreased with lung injury, Waveforms ranged from pure sinusoidal to a complex square wave. The handling of inspiration/expiration time ratios was ventilator specific, The SensorMedics inspiration/expiratio n ratio is user selected over a range from 1:2.3 (30% inspiratory time ) to 1:1 (50% inspiratory time) and once selected it is consistent ove r its entire range of operating frequencies, The Drager ratio is machi ne determined and varied from 1:2.5 at 5 Hz to 1:1 at 15 Hz, Inspirato ry time of the Infant Star is machine set at 18 msecs such that the in spiration/expiration ratio is 1:10.1 at 5 Hz and 1:2.7 at 15 Hz, The H umming V has a fixed inspiration/expiration ratio of 1:1, The relation ship of the mean airway pressure displayed on the ventilator to the al veolar occlusion pressure varied considerably among devices, The displ ayed mean pressure could either overestimate (SensorMedics at 33% insp iratory time or Infant Star), approximate (Humming V), or underestimat e (Drager) the mean lung distending pressure measured during a brief o cclusion maneuver, Conclusions: The findings demonstrate large variati ons in machine performance. The ventilators also differed profoundly i n complexity of operation and versatility as neonatal ventilators.