Page 249 - Clinical Application of Mechanical Ventilation

Initiation of Mechanical Ventilation 215

TABLE 8-2 Indications for Mechanical Ventilation

Indication Examples

1. Acute ventilatory failure Apnea or bradypnea
Acute lung injury (ALI) or Acute
respiratory distress syndrome
(ARDS)
pH ,7.30, PaCO .50 mm Hg
2
2. Impending ventilatory Progressive acidosis and
failure hypoventilation to pH ,7.30
and PaCO .50 mm Hg
2
Spontaneous frequency .30/min

3. Severe hypoxemia PaO ,40 mm Hg, SaO ,75%
2
2
PaO /F O (P/F ratio): ≤300 mm Hg for
P/F ratio: PaO 2 / F I O 2 . Clinical 2 I 2
assessment of oxygenation and de- ALI, ≤200 mm Hg for ARDS
gree of hypoxemia, ≤300 mm Hg
for ALI, ≤200 mm Hg for ARDS. 4. Prophylactic ventilatory Postanesthesia recovery
support Muscle fatigue
Neuromuscular disease
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TABLE 8-3 Assessment of Acute Ventilatory Failure

Parameter Limit

PaCO 2 .50 mm Hg (higher for COPD patients)

pH ,7.30
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documented by the PaCO , then the patient may be supported with supplemental
2
oxygen or continuous positive airway pressure (CPAP) or bilevel positive airway
pressure (BiPAP). Table 8-3 shows some common methods to assess the presence of
acute ventilatory failure.

Impending Ventilatory Failure

Impending ventilatory failure occurs when a patient can maintain only marginally
normal blood gases, but only at the expense of a significantly increased work of
breathing. Depending on the pulmonary reserve and lung function of a patient,
the PaCO value may be normal or low at the beginning of impending ventila-
2
tory failure. This is because of an increase in minute ventilation in an attempt to

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