Monday, January 23, 2006

Tuesday January 24, 2006

Conventional mechanical ventilation is provided at a rate < 2 Hz (1 Hz = 60 breaths/min). With high frequency ventilation (HFV), rates are provided at 2 – 15 Hz. The frequency range is determined by the specific technique and the size of the patient. Regardless of the technique, adults are generally ventilated at the low end of the rate spectrum and neonates at the high end of the spectrum. There are three techniques that have been classified as high frequency ventilation:

High frequency positive pressure ventilation (HFPPV)
High frequency Oscillation (HFO)
High frequency jet ventilation (HFJV)

conventional ventilators are used to provide rates at the low end of the HFV spectrum.

HFO has both an active inspiratory and expiratory phase. Oscillators establish gas flow by the movement of a diaphragm or piston, perpendicular to a bias flow that moves across the airway. With HFO, rates across the whole frequency spectrum are possible but in general 10 to 15 Hz range are most common with neonates and 3 to 8 Hz range are used with adults. The two conceptual advantages to HFO are lower peak airway pressures and the fact that non bulk-flow mechanisms may improve V/Q matching. Inadequate humidification is a well-known complication when using high gas flows and delivered minute volumes and may result in necrotizing tracheobronchitis. HFO may also cause direct physical airway damage.

During HFJV, gas under high pressure is injected into the airway with a secondary gas source entrained to provide tidal volume. With the HFJV, both a jet ventilator and conventional ventilator may be needed to establish gas delivery in the low to middle part of the HFV rate spectrum. This form of ventilation is mostly used in the operating room where a surgeon is working in the airway (laser Rx of papilloma on vocal cords) and an ETT cannot be placed or as an emergency airway. It is also used in the treatment of a disrupted airway or massive bronchopleural fistula as the non-bulk flow of gas decreases the amount of gas escaping out of the fistula. HFJV has been approved by the FDA for ventilating patients in whom a large and persistent bronchopleural fistula has developed.

See nice Review article
HIGH FREQUENCY OSCILLATORY VENTILATION: Clinical Management from VIASYS. (more details/tools at site). has no connection with VIASYS and info here is solely for educational purpose.

References: Click to get abstract/article
1. Schuster, DP, Klain, M, Snyder, JV.
Comparison of high frequency jet ventilation to conventional ventilation during severe acute respiratory failure in humans. Crit Care Med 1982 Oct;10(10):625-30.
2. Holzapfel, L, Robert, D, Perrin, F, et al.
Comparison of high-frequency jet ventilation to conventional ventilation in adults with respiratory distress syndrome. Intensive Care Med 1987; 13:100.
3. Fort, PF, Farmer, C, Westerman, J, et al.
High-frequency oscillatory ventilation for adult respiratory distress syndrome. Crit Care Med 1997; 25:937.
4. Mehta, S, Granton, J, MacDonald, RJ, et al.
High-frequency oscillatory ventilation in adults: the Toronto experience. Chest 2004; 126:518.