High frequency ventilation is a type of mechanical ventilation
that employs very high respiratory rates (>150 breaths per
minute) and very small tidal volumes (usually below anatomical
dead space). The primary goal of HFV is to achieve ventilation
and oxygenation at a reduced risk of ventilator induced lung
injury (VILI). This is commonly referred to as lung protective
ventilation. Ventilator induced lung injury is caused by
multiple factors. The human lung is designed to ventilate
effectively by using negative pressure in the thorax. Once
positive pressure is applied, some degree of VILI is likely to
occur. One major causative factor is the over stretching of the
airways and alveoli. During mechanical ventilation, the flow of
gas into the lung will take the path of least resistance. Areas
of the lung that are collapsed (atelectasis) or filled with
secretions will be under inflated, while those areas that are
relatively normal will be over inflated. These areas will become
over distended and injured. This may