Page 443 - Clinical Application of Mechanical Ventilation

Management of Mechanical Ventilation 409

lung and may increase the incidence of barotrauma (volutrauma). Therefore, the
barotrauma (volutrauma): Air
leak into the pleural space caused traditional approach in the selection of tidal volume may exacerbate or perpetuate
by excessive pressure or volume in lung injury in patients with ALI or ARDS and increase the risk of mortality and
the lung parenchyma.
nonpulmonary organ and system failure (Petrucci et al., 2004; The Acute Respira-
tory Distress Syndrome Network, 2000).

Volume Selection. In volume-targeted ventilation for patients with ALI or ARDS,
The tidal volume selected
for patients with ALI or ARDS the tidal volumes selected should result in a plateau pressure of ,35 cm H O
2
should result in a plateau (Thompson et al., 2001). Plateau pressure is used as a target pressure because it
pressure of ,35 cm H 2 O.
reflects the condition of the lung parenchyma. For the reason of lung protection,
the lowest tidal volume that meets the patient’s minimal oxygenation and ventila-
tion requirements should be used.

Complications. Use of low tidal volume ventilation should be done with care as it
may lead to complications such as acute hypercapnia, increased work of breathing,
dyspnea, severe acidosis, and atelectasis (Kallet et al., 2001).

Prone Positioning

Prone positioning (PP) has been used as a “stop-gap” strategy to improve the
prone positioning (PP): Place-
ment of the patient in a face-down ventilation, oxygenation, and pulmonary perfusion status of patients with acute
position in a bed. respiratory failure and ARDS. Following PP, there is a rapid increase in oxygen-
ation measurements (e.g., SpO , PaO , SaO ) and improvement in lung compli-
2
2
2
ance (Relvas et al., 2003). The oxygen requirement, intrapulmonary shunting, and
inspiratory pressures are reduced as well (Breiburg, 2000; Fletcher et al., 2003).
PP has been used
to improve ventilation, Table 12-20 outlines the physiologic goals of PP.
oxygenation, and pulmonary
perfusion in patients with While PP improves these pulmonary parameters rapidly, the improvements do
acute respiratory failure and not persist after the patient is returned to the original supine position. In addi-
ARDS.
tion, prone positioning does not increase the survival rate of patients with acute

TABLE 12-20 Physiologic Goals of Prone Positioning

To improve oxygenation (e.g., SpO , PaO , SaO )
2
2
2
To improve respiratory mechanics (e.g., compliance, work of breathing)
To enhance pleural pressure gradient, alveolar inflation, and gas
distribution
To reduce inspiratory pressures (e.g., peak and plateau)

To reduce atelectasis and intrapulmonary shunting

To facilitate removal of secretions
To reduce ventilator-related lung injury

(Data from Breiburg, 2000; Fletcher et al., 2003; Pelosi et al., 2002; Relvas et al., 2003.)
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