Page 528 - Clinical Application of Mechanical Ventilation

494 Chapter 15

Lung Protection using Airway Pressure Thresholds

Studies have shown that lung injuries during mechanical ventilation are associ-
ated with high airway pressures. Barotrauma or volutrauma is one of the severe
complications of positive pressure ventilation. In patients with ARDS and reduced
compliance, high peak inspiratory pressure is usually required because of the low
lung compliance. The increase in airway pressures has the potential to injure the
lung units that have normal or high compliance. Positive pressure ventilation can
lung protection strategy: A also cause lung injuries such as pneumomediastinum, pneumoperitoneum, pneu-
method to prevent the lungs from mothorax, tension pneumothorax, and subcutaneous emphysema (Bezzant et al.,
pressure- or volume-induced inju-
ries during mechanical ventilation. 1994; Slutsky, 1994).
Lung protection strategy is a method to prevent the lungs from pressure- or
volume-induced injuries during mechanical ventilation. The general agreement of
Risk of barotrauma may lung protection is to use the lowest pressures (i.e., PIP, P PLAT , mPaw) or tidal volume
be reduced by keeping the PIP possible. Studies recommend that, in most cases, the airway pressures should be
,50 cm H 2 O, P PLAT ,35 cm
H 2 O, mPaw ,30 cm H 2 O, and kept as follows: peak inspiratory pressures ,50 cm H O, plateau pressures ,35 cm
2
PEEP ,10 cm H 2 O. In 2000,
the ARDSNet recommended H O, mean airway pressures ,30 cm H O, and PEEP ,10 cm H O (Bezzant
2
2
2
plateau pressure ,30 cm et al., 1994; Slutsky, 1994). (Note: In 2000, the ARDSNet recommended plateau
H 2 O.
pressure ,30 cm H O.)
2
The suggested thresholds on airway pressures should be used as a guideline. De-
pending on the patient and other coexisting conditions, the pressure thresholds
must be adjusted as indicated.
Low Tidal Volume and Permissive Hypercapnia

High airway pressure and high tidal volume increase the risk for ARDS in pa-
tients receiving mechanical ventilation for greater than 48 hours (Jia et al., 2008).
Low tidal volume and permissive hypercapnia are two strategies that can partially
permissive hypercapnia: A lung
protection method that uses low minimize these risk factors. The primary advantage of using low tidal volume or
tidal volume (i.e., 4 to 7 mL/Kg) permissive hypercapnia is to minimize the airway pressures and to reduce the risk
and allows the PaCO 2 to rise above
50 mm Hg. for barotrauma (Feihl et al., 1994; Hall et al., 1987).
Low Tidal Volume. In patients with high lung compliance, increased functional re-
sidual capacity and air trapping, barotrauma is likely due to preferential distribu-
For patients with COPD, tion of mechanical tidal volume to lung units with high compliance. Patients with
the tidal volume should be
reduced. The peak inspiratory COPD are candidates of acquiring overdistention, air trapping, and auto-PEEP
flow should be increased to during positive pressure ventilation. For these patients, the tidal volume should be
allow a longer expiratory time
for adequate exhalation. reduced. The peak inspiratory flow should be increased to allow a longer expiratory
time for adequate exhalation.
Mechanical ventilation with low tidal volume increases deadspace ventilation
and decreases alveolar ventilation. Complications of the low tidal volume method
Mechanical ventila- include acute hypercapnia and respiratory acidosis, increased work of breathing,
tion with low tidal volume
increases deadspace ventila- dyspnea, and atelectasis (Kallet et al., 2001a and 2001b).
tion and decreases alveolar
ventilation. Permissive Hypercapnia. Permissive hypercapnia uses low tidal volume during volume-
controlled ventilation and allows the PaCO to rise above the upper-normal limit
2

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.