High-frequency ventilation
In general, those devices that need conventional mechanical ventilation do not produce the same lung protective effects as those that can operate without tidal breathing.
With high-frequency ventilation, the tidal volumes used are smaller than anatomical and equipment dead space and therefore alternative mechanisms of gas exchange occur.
[citation needed] High-frequency jet ventilation (HFJV) minimizes movement of the thorax and abdomen and facilitates surgical procedures where even slight motion from spontaneous or intermittent positive pressure ventilation may significantly affect the duration and success of the procedure (for example atrial fibrillation ablation).
HFJV does NOT allow: setting specific tidal volume, sampling ETCO2 (and because of this, frequent ABGs are required to measure PaCO2).
This combination of small tidal volumes delivered for very short periods of time creates the lowest possible distal airway and alveolar pressures produced by a mechanical ventilator.
Usage of high-frequency jet ventilation is recommended in neonates and adults with severe lung injury.
Infants of this description studied ranged in birth weight from 600 to 3660 grams and in gestational age from 24 to 38 weeks.
These adverse effects include: High-frequency jet ventilation is contraindicated in patients requiring tracheal tubes smaller than 2.5 mm ID.
Settings that can be adjusted in HFJV include 1) inspiratory time, 2) driving pressure, 3) frequency, 4) FiO2, and 5) humidity.
HFOV is often used in premature neonates with respiratory distress syndrome who fail to oxygenate appropriately with lung-protective settings of conventional ventilation.
It has also been used in ARDS in adults, but two studies (the OSCAR and OSCILLATE trials) showed negative results for this indication.
HFPPV is delivered through the endotracheal tube using a conventional ventilator whose frequency is set near its upper limits.
It has been used to salvage patients with persistent hypoxemia when on conventional mechanical ventilation or, in some cases, used as a primary modality of ventilatory support from the start.
[6][7] HFFI — High Frequency Flow Interruption is similar to high-frequency jet ventilation but the gas control mechanism is different.
Frequently a rotating bar or ball with a small opening is placed in the path of a high pressure gas.
Active exhalation means a negative pressure is applied to force volume out of the lungs.
[9] HFOV is characterized by high respiratory rates between 3.5 and 15 hertz (210 - 900 breaths per minute) and having both inhalation and exhalation maintained by active pressures.
Different mechanisms (direct bulk flow - convective, Taylorian dispersion, Pendelluft effect, asymmetrical velocity profiles, cardiogenic mixing and molecular diffusion) of gas transfer are believed to come into play in HFOV compared to normal mechanical ventilation.
It is often used in patients who have refractory hypoxemia that cannot be corrected by normal mechanical ventilation such as is the case in the following disease processes: severe ARDS, ALI and other oxygenation diffusion issues.
The higher amplitudes at lower frequencies will cause the greatest fluctuation in pressure and move the most gas.
The mean airway pressure will change and requires the mean pressure adjust to be adjusted when the following settings are changed: During high-frequency oscillatory ventilation (HFOV), PAW is the primary variable affecting oxygenation and is set independent of other variables on the oscillator.
The power setting interacts with PAW conditions existing within the patient circuit to produce the resulting ΔP.
Such as Treacher Collins syndrome, Robin sequence, head and neck surgery with supraglottic or glottic obstruction).
