Page 150 - Clinical Application of Mechanical Ventilation

116 Chapter 4

HFOV delivers a constant flow (bias flow) and its piston pump oscillates at fre-
In HFOV, ventilation can quencies ranging from 3 Hz to 15 Hz (180 breaths/min to 900 breaths/min). Adult
be increased by decreasing the
oscillation frequency. Ventila- patients are sedated to prevent deep spontaneous breathing, as this will trigger the
tion can also be increased by alarms and affect ventilator performance.
increasing the amplitude of
the oscillations, inspiratory Ventilation can be increased by decreasing the oscillation frequency (in traditional
time, or bias flow (with an ventilators, the frequency would be increased). Ventilation can also be increased by
intentional cuff leak).
increasing the amplitude of the oscillations, increasing the inspiratory time, or in-
creasing the bias flow (with an intentional cuff leak). Oxygenation to the patient can
be increased by increasing the mean airway pressure or increasing the F O . Topics
In HFOV, oxygenation to I 2
the patient can be increased related to high frequency ventilation will be discussed in more details in Chapter 17,
by increasing the mean airway “Neonatal Mechanical Ventilation.”
pressure or increasing the F I O 2 .

SUMMARY

There are many different ventilator operating modes and the number is expected to
increase in coming years. As each mode is designed to accomplish a set of specific
functions, it is essential to understand its capabilities, as well as its limitations and
complications. When two or more operating modes are used in tandem, care and
caution must be used because the combined outcomes are often complex and difficult
to predict or manipulate.
An excellent source of obtaining detailed technical information is to consult the op-
eration manual or contact the technical professionals of each ventilator manufacturer.
Quality patient care is possible when the appropriate operating modes are selected
and applied. A willingness to participate in continuing education is highly desirable
and sometimes mandatory in this ever-changing field of mechanical ventilation.

Self-Assessment Questions

1. Volume-controlled ventilation delivers a predetermined _______ to the patient using variable _______
according to the changing compliance and resistance.
A. tidal volume, peak inspiratory pressure
B. peak airway pressure, tidal volume pressure
C. tidal volume, PEEP
D. PEEP, pressure support

2. During pressure-controlled ventilation, an increase of airway resistance or a decrease of compliance would:

A. reduce the delivered volume.
B. raise the peak inspiratory pressure.
C. reduce the work of breathing.
D. cause respiratory alkalosis.

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