Page 564 - Clinical Application of Mechanical Ventilation

530 Chapter 16

circumstances, there are other modes of ventilation that provide partial ventilatory
support (MacIntyre et al., 2001). These modes are volume support, volume-assured
pressure support, mandatory minute ventilation, and airway pressure-release venti-
lation. For a more detailed discussion on these modes, refer to Chapter 4, Operating
Modes of Mechanical Ventilation.
Volume support (VS) and volume-assured pressure support (VAPS) are a form
of PSV that “guarantees” a preset tidal volume. In VS, the pressure support level
is adjusted automatically to achieve the target tidal volume. In VAPS, it guaran-
tees a preset tidal volume by incorporating inspiratory pressure support ventila-
tion (PSV) with conventional volume-assisted cycles (VAV). Unlike typical PSV,
VAPS assures stable tidal volume in patients with irregular breathing patterns. By
decreasing the frequency, the work of breathing is shifted from the ventilator to
the patient.
Mandatory minute ventilation (MMV) is a form of SIMV in which the min-
ute ventilation is guaranteed. The ventilator adjusts the frequency automatically to
achieve the target minute ventilation. By decreasing the MMV level, the patient
assumes more spontaneous breathing.
Airway pressure-release ventilation (APRV) has two pressure levels: the higher
airway pressure (e.g., 10 cm H O) and the lower release pressure (usually 0 cm
2
H O). The tidal volume is determined by the pressure gradient between the
2
airway pressure and the release pressure. In APRV, exhalation occurs during
pressure release and inhalation occurs when the pressure returns to the airway
pressure. Weaning may be done by decreasing the frequency of pressure release.
When the frequency of pressure release is zero, the patient is essentially on a
CPAP mode.

WEANING PROTOCOL

Weaning protocol and clinical practice guidelines for weaning are primarily
used to outline the standard of care for the purpose of weaning from mechanical
ventilation. In general, they often include three elements: the patient condition in
which weaning may be attempted, the detailed process of weaning, and the evalu-
ation of weaning outcomes.
There are many weaning protocols published in the literatures or developed
by individual hospitals or departments. Each of them can be useful when the
elements of weaning are incorporated with sound clinical reasoning and imple-
mentation. The criteria in the weaning protocol should be used as guidelines
only and must not be carried out using a “cookbook” approach. Individual pa-
tient differences must also be considered since disease processes and patient
characteristics are two of many variables that may affect the outcomes of a wean-
ing protocol (Keenan, 2002). Weaning protocols range from simple to com-
plex. Table 16-6 provides a simple weaning protocol for mechanical ventilation
(Grap et al., 2003).

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.