Page 248 - Clinical Application of Mechanical Ventilation

214 Chapter 8

TABLE 8-1 Goals of Mechanical Ventilation

Goal Target

1. Improve gas exchange Reverse hypoxemia
Relieve acute respiratory acidosis
2. Relieve respiratory distress Reduce oxygen cost of breathing
Reverse respiratory muscle fatigue

3. Improve pulmonary mechanics Prevent and reverse atelectasis
Improve compliance
Prevent lung injury
4. Permit lung and airway healing Maintain lung and airway
functions

5. Avoid complications Protect lung and airway
Prevent disuse respiratory
muscle dystrophy
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INDICATIONS

Mechanical ventilation is indicated when the patient cannot maintain spontane-
Mechanical ventilation ous ventilation to provide adequate oxygenation or carbon dioxide removal. The
is indicated when the patient
cannot maintain spontane- clinical conditions leading to mechanical ventilation can be grouped into four
ous ventilation to provide areas: (1) acute ventilatory failure; (2) impending ventilatory failure; (3) severe
adequate oxygenation or
carbon dioxide removal. hypoxemia; and (4) prophylactic ventilatory support (Brown, 1994; Otto, 1986).
Table 8-2 outlines the indications for mechanical ventilation.

acute ventilatory failure: An Acute Ventilatory Failure
increase of PaCO 2 (.50 mm Hg)
with a concurrent decrease of
arterial (pH ,7.30). The primary indication for mechanical ventilation is acute ventilatory failure. This
is defined as a sudden increase in the PaCO to greater than 50 mm Hg with an
2
accompanying respiratory acidosis (pH 67.30). In the COPD patient, mechani-
impending ventilatory cal ventilatory support is indicated by an acute increase in the PaCO above the
failure: A gradual increase of 2
PaCO 2 (.50 mm Hg) caused by patient’s normal baseline PaCO accompanied by a decompensating respiratory
2
deteriorating lung functions.
acidosis (Brown, 1994; Otto, 1986).
Other signs that may be useful in the assessment of acute ventilatory failure in-
clude apnea, bradypnea, ALI, and ARDS (Byrd et al., 2010). However, mild to
prophylactic ventilatory
support: Early intervention of moderate hypoxemia (PaO 5 50 to 60 mm Hg or SaO 5 85% to 90%) does
2
2
potential ventilatory failure by not by itself indicate the presence of acute ventilatory failure or the need for ven-
means of mechanical ventilation.
tilatory support. If a hypoxemic patient is able to maintain adequate ventilation as

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