High Frequency Ventilation

High Frequency Positive Pressure Ventilation (HFPPV)

60-120/min, small volumes. Can be open (ex. catheter in the mouth, output of gas does not follow any particular path) or closed (ex. catheter through an ETT, in which the outflow of gas follows a predetermined pathway). Closed is superior although not always possible. Can be used to ventilate both lungs (or just the operative lung), although when used on the operative lung is oftentimes disruptive (because it increases the diameter of central airways). It is therefore most useful in thoracic non-pulmonary surgery (ex. esophageal, thoracic aorta). At high frequencies (> 6 Hz), CO2 retention may become problematic.

High Frequency Jet Ventilation (HFJV)

100-400/min of 50 psig gas. Open or closed systems are possible. Can be used to deliver volatile anesthetics, and has been successfully used in the operative lung (with traditional ventilation in the dependent lung). The major theoretical advantage of HFJV over CPAP in the operative lung is its relative hemodynamic stability (it has been shown to have less of an effect on cardiac output), however because of the cumbersome equipment involved, it is less commonly used. HFJV is ideal for bronchopulmonary fistulas, as it involves relatively low intrapulmonary pressures. It is also ideal in situations in which a particular region needs ventilation, as the surgeon can place a HFJV catheter in the region of interest.

High Frequency Oscillation Ventilation (HFOV)

400-2400/min, VT 50-80 mL. Gas exchange occurs primarily through molecular diffusion and coaxial airway flow.