Page 595 - Clinical Application of Mechanical Ventilation

Neonatal Mechanical Ventilation 561

Clinical Use. HFJV is used in tandem with conventional ventilators. The purpose
of the conventional ventilator is threefold. First, it provides occasional sighs that
help stimulate the production of surfactant and prevent microatelectasis. Second,
the conventional ventilator provides PEEP to the patient’s airway. Third, it makes
a continuous flow of gas available at the endotracheal tube for entrainment by the
jet ventilator (Gordin, 1989).

Hazards. The principal hazard of HFJV is damage to the trachea and large airways,
The principal hazard of
HFJV is damage to the trachea leading to necrotizing tracheobronchitis. Originally thought to be caused by poor
and large airways, leading to humidification, it is now believed to be caused by the impact of the high pressure
necrotizing tracheobronchitis.
gas “bullets” on the wall of these airways (Milner & Hoskins, 1989).
To offset damage, HFJV should only be delivered through a special catheter that
exits internally to the endotracheal tube or via a special triple-lumen endotracheal
tube, previously mentioned. The triple-lumen tube incorporates the jet injector and
a pressure monitoring port in the lumen of standard-sized endotracheal tubes.
Other hazards include gas trapping, hyperinflation, obstruction of the airway
To minimize tracheal with secretions, hypotension, and inflammatory injury to the trachea (Gordin,
damage, the high pressure
pulse of gas exits inside the 1989; Richardson, 1988).
endotracheal tube via a Of concern with the use of HFJV is the difficulty encountered in assessing the pa-
special tube.
tient. Auscultation of breath sounds and heart sounds is difficult due to the constant
vibration and noise produced by the ventilator. Assessment of these patients is based
on the observation of other clinical signs. Decreased lung compliance and pneu-
mothoraces are observed by a decrease in chest wall vibration, increased PaCO ,
2
Transillumination of the and a decreased PaO . Transillumination of the infant chest can be used to detect
2
infant chest can be used to tension pneumothorax. A decrease in chest wall vibration and an increase in PaCO ,
detect tension pneumothorax. 2
without a drop in PaO , indicate an obstruction or malposition of the endotracheal
2
tube. Microatelectasis and hyperinflation may be seen clinically as a decrease in the
PaO . Neonates on HFJV should also be closely monitored for fluid, electrolyte,
2
and neurological status (Gordin, 1989).

High Frequency Oscillatory Ventilation (HFOV)

High frequency oscillatory ventilation (HFOV) utilizes the highest of frequencies,
usually in the range of 480–1,800/min (8 to 30 Hz). A piston pump produces the
oscillatory waves that deliver the gas to the lungs.
Concept of Operation. A unique feature of HFOV is that it produces a positive as well
as a negative stroke, which assists both inspiration and expiration (Figure 17-3). The
HFOV device is placed inline with the endotracheal tube and a gas source is passed
perpendicularly into the tube, as illustrated in Figure 17-4.
As the fresh gas enters the endotracheal tube, it is driven to the patient by the
waves coming from the oscillator. Expiration occurs opposite to where the gas en-
ters the endotracheal tube through an expiratory limb that has a high impedance to
oscillations, but a low impedance when there is a steady flow of gas. Modern HFOV
devices use traditional endotracheal tubes and are not used in tandem with conven-
tional ventilators (Meredith, 1995).

Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.