Causes of Hypoxia
- Inadequate Oxygen Delivery: inadequate minute ventilation or FiO2; mechanical failure, disconnect
- R-L Shunt: intracardiac shunting
- V/Q Mismatch: mainstem, pulmonary edema, aspiration, atelectasis, pulmonary embolus
- Impaired Diffusion: pulmonary edema, pneumonia
Note that despite the separate classifications above, most cardiopulmonary pathology contributes to hypoxemia via multiple mechanisms (ex. emphysema causes hypoventilation, diffusion impairment, and V/Q mismatch, see Miller Table 15-2)
The causes of high airway pressures and low exhaled volumes described above can result in hypoxia if they cause hypoventilation.
Despite the use of numerous safety precautions, cases are occasionally documented of ventilators being connected to compressed air or nitrous oxide instead of oxygen.
EXCLUDE equipment failure and mechanical causes of hypoxia. Increase FiO2. Check ETCO2 (will alert you to hypoventilation or increased deadspace, ex. PE). Increase PEEP or minute ventilation. Consider recruitment breaths. Consider bronchoscopy and suctioning. ABG allows you to measure deadspace and A-a gradient.