Page 118 - Clinical Application of Mechanical Ventilation

84 Chapter 4

useful in selected home care settings because of the ease to maintain and the capa-
bility to ventilate without an artificial airway. All subsequent discussions on me-
chanical ventilation in this text refer to positive pressure ventilation unless negative
pressure ventilation is specifically mentioned.

Positive Pressure Ventilation

Positive pressure ventilation is achieved by applying positive pressure (a pressure
The tidal volume deliv- greater than atmospheric pressure) at the airway opening. Increasing the pressure
ered by a positive pressure
ventilator is directly related to at the airway opening produces a transairway pressure gradient that generates an
the positive pressure gradient. inspiratory flow. This flow, in turn, results in the delivery of a tidal volume. There-
fore, tidal volume is directly related to the transairway pressure gradient. All other
factors being held constant, increasing the positive pressure being applied to the
lungs will result in a larger tidal volume being delivered.

OPERATING MODES OF MECHANICAL VENTILATION

A ventilator mode can be defined as a set of operating characteristics that control
how the ventilator functions. An operating mode can be described by the way a
ventilator is triggered into inspiration and cycled into exhalation, what variables are
limited during inspiration, and whether or not the mode allows mandatory breaths,
intermittent breaths, or spontaneous breaths.
Many additional operating functions are also available on modern ventilators.
Some examples are control of the F O , control of the inspiratory flow rate, and
I
2
control of various alarms.
Regardless of which operating mode is selected, it should achieve four main goals:
provide adequate ventilation and oxygenation, avoid ventilator-induced lung injury,
provide patient-ventilator synchrony, and allow successful weaning from mechani-
cal ventilation. Table 4-1 provides an overview of the mechanical breath terminol-
ogy that should enhance an understanding in the selection and use of different
operating modes (Mireles2Cabodevila et al., 2009). Common operating modes
will be reviewed separately in this chapter.
There are at least 23 modes of ventilation available in different ventilators. Two or
more of these modes are often used together to achieve certain desired effects. For
example, spontaneous plus PEEP is the same as CPAP, and it is used to oxygenate
a patient who has adequate spontaneous ventilation. SIMV may be used with PSV
to provide mechanical ventilation and reduce the work of spontaneous breathing.

1. Spontaneous
2. Positive end-expiratory pressure (PEEP)
3. Continuous positive airway pressure (CPAP)
4. Bilevel positive airway pressure (BiPAP)

5. Controlled mandatory ventilation (CMV)
6. Assist/control (AC)

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.