VT PLUS HF performance verification of Bunnell Life-Pulse HFJV (High Frequency Jet Ventilator)
VT PLUS HF provides a special mode for evaluating the performance of high frequency ventilators while connected to the patient ypiece of ventilator breathing circuit. A proper test load (calibrated test lung) should always be used to evaluate the performance of ventilators compared to their manufacturer’s specifications and to ensure the ventilator will perform according to clinical expectations in real-use scenarios.
Brief HFJV intended use and theory of operation:
HFJV is a method of delivering oxygen-rich gases into the lungs to promote gas exchange across the lung-unit (alveoli)-to-blood tissue partition. The way that HFJV does this is by delivering the gas flow over short Inspiratory times (I-times), which provide two of the most important benefits of H F J V :
- small tidal v o l u m e s
- low alveolar pressures.
Small tidal volumes, when delivered with short I-times, make it impossible for the peak pressure used during HFJV to be transmitted to alveoli, thus protecting them.
Squirting gas into the ET tube at high velocity allows gas to penetrate deeper into the lung with each breath, penetrating through dead space gas instead of pushing it ahead of the fresh gas. Delivering fresh gas in this way minimizes the size of each breath and pressure needed to deliver it to the aveoli. With fresh gas shooting down the center of the airways slower moving passive expiratory gas flow moves out along the airway walls. This countercurrent pattern facilitates airway clearance as shown in the following illustration.
PEEP controls mean airway pressure during HFJV, and MAP determines mean lung volume. Optimal PEEP/MAP facilitates oxygenation without the use of continual CV breaths. This strategy relegates CV breaths to intermittent use for alveolar recruitment.