Hypoxemia

An abnormally low concentration of oxygen in the arterial blood (PaO₂ <10.6 kPa or <80 mmHg), reflecting impaired pulmonary gas exchange or oxygenation of circulating blood.

Causes

• Pulmonary causes

  • Chronic obstructive pulmonary disease (COPD)

  • Asthma

  • Pneumonia

  • Acute respiratory distress syndrome (ARDS)

  • Interstitial lung disease with pulmonary fibrosis

  • Pulmonary embolism

  • Pneumothorax

  • Pulmonary edema

  • Atelectasis

  • Alveolar hypoventilation

  • Ventilation–perfusion (V/Q) mismatch

  • Diffusion impairment

  • Intrapulmonary shunting

• Cardiovascular causes

  • Heart failure

  • Right-to-left cardiac shunts

  • Congenital heart disease causing shunting

• Sleep-related causes

  • Obstructive sleep apnea

  • Obesity hypoventilation syndrome

• Environmental causes

  • High altitude

  • Low inspired oxygen concentration

• Medication and substances causing respiratory depression

  • Narcotics (opioids)

  • General anesthetics

  • Sedatives

• Other causes

  • Severe anemia causing reduced oxygen content despite normal PaO₂

  • Neuromuscular disorders causing respiratory failure

  • Chest wall deformities impairing ventilation