Table I.
Mechanisms of hypoxemia with examples.
| Mechanism of hypoxemia | Example |
|---|---|
| Low FiO2 | High altitude Anesthetic accidents in which oxygen source is reduced, occluded, or otherwise not appropriate for the patient |
| Hypoventilation | Cervical myelopathy |
| Reduced movement of air into and out of the alveoli | Neuromuscular disease Sedation/anesthesia |
| Diffusion impairment | Interstitial lung disease (smoke inhalation, ARDS) |
| Thickening or other abnormality of the alveolar interstitial membrane reducing gas exchange | Pulmonary fibrosis |
| High V:Q mismatch | Pulmonary thromboembolism |
| Ventilation normal (normal oxygen delivery to alveoli), pulmonary blood flow compromised | Atelectasis |
| Low V:Q mismatch | Pulmonary edema |
| Ventilation compromised (low oxygen delivery to alveoli), pulmonary blood flow normal | Pneumonia Pulmonary neoplasia |
| Right to left anatomic shunts | Right to left patent ductus arteriosus Ventricular septal defect |
FiO2 — Fraction of inspired oxygen; ARDS — Acute respiratory distress syndrome; V — Ventilation; Q — Perfusion.