Page 596 - Clinical Application of Mechanical Ventilation

562 Chapter 17

Gas Flow
to Patient

Inspiration

Gas Flow
from Patient
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Expiration
Figure 17-3 In high frequency oscillatory ventilation (HFOV), positive and negative strokes
are provided to assist both inspiration and expiration.

Theories of Gas Exchange. A phenomenon, called pendelluft, occurs when inflated
alveolar units equilibrate gases by swinging ventilations between them. This serves
to improve gas exchange and impact enhanced diffusion (Higginson, 2002). With
all theories of gas exchange during HFV, it may be easiest to just say “Our under-
standing of this complex set of gas exchange dynamics remains incomplete” (Walsh
et al., 2010). Even those who experiment, compute, and mathematically examine
these theories, conclude that what happens in simulations may not be what is hap-
pening in real lungs (Pedley et al., 1994). See Figure 17-4.
Indications. HFOV should be considered when conventional ventilation fails to pro-
vide adequate ventilation or oxygenation to neonates of all birth weights and gesta-
tional ages (Clark et al., 1994; Grenier & Thompson, 1996). Additionally, in recent
years, studies have been done on neonates who were placed directly on HFOV and

Oscillator

Mixed Expired Gas Through
Gas Flow Low Pass Filter

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Endotracheal
Tube
Figure 17-4 The oscillator or high frequency oscillatory ventilation (HFOV) device is placed
in-line with the endotracheal tube and a gas source is passed perpendicularly into the tube.

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