Page 593 - Clinical Application of Mechanical Ventilation

Neonatal Mechanical Ventilation 559

TABLE 17-8 Classification of High Frequency Ventilation

Type Of High Frequency Ventilator Frequency (Hertz)* Frequency (Cycles Per Min)

High frequency positive pressure 1 to 2.5 Hz 60 to 150
ventilation (HFPPV)

High frequency jet ventilation 4 to 11 Hz 240 to 660
(HFJV)
High frequency oscillatory 8 to 30 Hz 480 to 1800
ventilation (HFOV or HFO)

*1 Hertz (Hz) 5 1 cycle per sec or 60 cycles per min.
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conventional ventilation are often inclusive, the results may be dependent upon
when HFV is introduced as a means of ventilation. Early intervention may result in
more desirable outcomes. Any conclusive outcomes will require additional research.
HFV is delivered at frequencies between 60 and 1,800 cycles per minute (breaths
HFV uses low pressures per minute). The major types of HFV are categorized by the frequency of ventila-
to deliver small tidal volumes.
This reduces the risk of tion and the method with which the tidal volume is delivered. The three categories
barotrauma. examined here are high frequency positive pressure ventilation, high frequency jet
ventilation, and high frequency oscillation (Table 17-8).

High Frequency Positive Pressure
Ventilation (HFPPV)

High frequency positive pressure ventilation (HFPPV) is simply conventional ven-
tilatory breaths delivered at frequencies between 60 and 150 breaths per minute
(1 to 2.5 Hz). The delivery of tidal volume during HFPPV appears to occur via con-
vective air movement, in which tidal volume exceeds deadspace (Boynton, 1986).
Modern neonatal ventilators can deliver HFPPV at frequencies up to 150/min.
Indications. HFPPV is indicated on those patients who are hypoxemic or hypercap-
HFPPV is indicated on
those patients who are hypox- nic despite adequate and appropriate conventional ventilation. Studies have shown
emic or hypercapnic despite a reduction in PaCO and in F O when HFPPV was used on these patients. These
adequate and appropriate 2 I 2
conventional ventilation. studies additionally showed a lower incidence of pneumothoraces in the neonates
ventilated with HFPPV when compared to those receiving conventional ventilation
(Boynton, 1986). There are also studies that have shown that patient-ventilator dys-
synchrony may be eliminated at ventilatory frequencies of 100 to 120 breaths per
minute (Milner & Hoskins, 1989).

Clinical Use. In the presence of severely noncompliant lungs, increases in peak in-
spiratory pressure may reach dangerous levels before an adequate tidal volume is
achieved. In these cases, the frequency is increased to increase minute ventilation,
allowing the peak pressure to remain lower. As frequencies increase (with sufficient
flow), the inspiratory time is decreased to allow adequate exhalation of the tidal

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