INDICATIONS FOR MECHANICAL VENTILATION

1. Hypoxemic respiratory failure

2. Hypercarbic respiratory failure

• Hypoxemic respiratory failure is present when arterial O2 saturation (SaO2) < 90% occurs

despite an inspired O2 fraction (FIO2) > 0.6.• The goal of ventilator treatment in this setting is to provide adequate SaO2 through a

combination of supplemental O2 and specific patterns of ventilation that improve V˙ /Q˙ matching and reduce intrapulmonary shunt.

Hypoxemic respiratory failure

Most commonly results from conditions such as • Pneumonia• pulmonary edema• pulmonary hemorrhage• respiratory distress syndrome

• Hypercarbic respiratory failure results from conditions that decrease minute ventilation or increase physiologic dead space such that

alveolar ventilation is inadequate to meet metabolic demands.

• Acute hypercarbic respiratory failure is characterized by arterial PCO2 values > 50 mmHg and an arterial pH < 7.30.

Clinical conditions associated with hypercarbic respiratory failure include

• Neuromuscular diseases, such as myasthenia gravis,

• Ascending polyradiculopathy,• Myopathies• Diseases that cause respiratory muscle fatigue

due to increased workload, such as asthma, chronic obstructive pulmonary disease, and

restrictive lung disease.