NEWBORN HIGH FREQUENCY VENTILATION

High-frequency ventilation: High-frequency ventilation (HFV) may improve blood gases because, in addition to the gas transport by convection, other mechanisms of gas exchange may become active at high frequencies (variable velocity profiles of gas during inspiration and exhalation, gas exchange between parallel lung units, increased turbulence and diffusion).Extensive clinical use of the various HFVs has occurred in newborns.

High-frequency positive-pressure ventilators employ standard ventilators modified with low-compliance tubing and connectors, thus an adequate tidal volume may be delivered despite very short inspiratory time. High-frequency jet ventilation (HFJV) is characterized by the delivery of gases from a high-pressure source through a small-bore injector cannula.

The fast gas flowing out of the cannula possibly produces areas of relative negative pressure that entrain gases from their surroundings. High-frequency flow interruption (HFFI) also delivers small tidal volumes by interrupting the flow of the pressure source, but in contrast to jet ventilation, HFFI does not use an injector cannula.

High-frequency oscillatory ventilation (HFOV) delivers very small volumes (even smaller than dead space) at extremely high frequencies. Oscillatory ventilation is unique because exhalation is generated actively, as opposed to other forms of HFV, in which exhalation is passive. The largest randomized trial of HFV revealed that early use of HFOV did not improve outcome.

However, the trend is toward decreases in BPD, increases in severe intraventricular hemorrhage and in periventricular leukomalacia, and small increases in air leaks with HFOV and/or HFFI. However, if used properly, HFV is a safe alternative for infants for whom CMV fails.