In the first blog, we wrote about the added value of jet ventilation. Now we will go further into how jet ventilation works and explain the differences between classic High Frequency Jet Ventilation (HFJV) with a thin jet catheter and Superimposed High Frequency Jet Ventilation (SHFJV). SHFJV is a form of jetting that can be applied with the Twinstream®.
In classic jet ventilation, ventilation occurs in an open airway by means of insufflation of gas at a very high speed through a narrow catheter (diameter 2.5 mm) and a ventilation frequency of >1 Hz. Below you can see the difference between ventilation with a tube and classic HFJV using a jet catheter.
Essential characteristics of HFJV are:
- Open system, free airway
- Low volumes, under high pressure and high speed
- Wide frequency scale: 60–2400 b/min
- Active inspiration and passive expiration
- Simultaneous inspiration and expiration
- Multiple gas flow principles ensure good gas exchange, including the Bernoulli and Venturi effects
Because the jet stream passes through a narrow catheter at high pressure, a suction effect of ambient air occurs at the outlet of the catheter. This venturi effect or air-entrainment therefore increases the Tidal Volume.
With jet ventilation, the higher the frequency, the better the oxygenation will be. At the same time, as the frequency increases, the CO₂ washout will decrease. By combining high-frequency ventilation with normoventilation, an optimal, tubeless ventilation can be created in which the HF jet flow generates the end-expiratory pressure plateau (PEEP) and the low-frequency jet flow provides the inspiratory pressure plateau (PIP).
Superimposed High Frequency Jet Ventilation
The combination of these gas flows is called Superimposed High Frequency Jet Ventilation. The SHFJV creates optimal gas exchange with low ventilation pressures. Below you see a schematic representation:
During jet ventilation, there are a number of settings that influence gas exchange:
- The working pressure of the jet stream; roughly speaking, a higher pressure means that air-entrainment increases;
- The frequency of jet ventilation; a higher frequency is positive with regard to the FiO₂ and reduces CO₂ washout;
- Adjusting the I:E ratio affects gas exchange.
During jet ventilation, it is recommended to heat and humidify the ventilation air. This takes place through an extra (bias) flow that is administered via a humidifier. As an additional advantage, this extra flow increases air-entrainment.
This table shows what a change in one of the settings accomplishes.
