Is hypoxia also a form of hypoxemia?

No, Hypoxia is NOT the Same as Hypoxemia

Hypoxia and hypoxemia are distinct but related concepts that must not be confused, as they require different diagnostic and therapeutic approaches. 1, 2

Key Definitions

Hypoxemia refers specifically to abnormally low partial pressure of oxygen (PaO2) or low oxygen content in the arterial blood, typically defined as PaO2 <8 kPa (60 mm Hg) or SaO2 <90%. 1, 2

Hypoxia is a broader term describing insufficient oxygen supply to meet metabolic demands at the tissue level, which can occur even when blood oxygen levels are normal. 2

Critical Clinical Distinction

The most important clinical pitfall is that normal oxygen saturation does not rule out tissue hypoxia—patients with adequate SpO2 may still have tissue hypoxia due to non-hypoxemic mechanisms. 2

Four Types of Hypoxia

1. Hypoxemic hypoxia: Results from low arterial PaO2 due to lung pathology (V/Q mismatch, shunt, diffusion impairment, alveolar hypoventilation, or reduced inspired oxygen). 1

2. Anemic hypoxia: Reduced oxygen-carrying capacity despite normal PaO2 and SpO2, caused by low hemoglobin or carbon monoxide poisoning. 1

3. Stagnant hypoxia: Inadequate tissue oxygen delivery due to low cardiac output or poor regional blood flow, even with normal arterial oxygen levels. 1

4. Histotoxic hypoxia: Inability of tissues to utilize oxygen due to mitochondrial dysfunction (e.g., cyanide poisoning, severe sepsis). 1

Management Implications

For Hypoxemia

• Oxygen therapy targeting SaO2 ≥94% for most acutely ill patients (88-92% for COPD/hypercapnic risk). 1, 2
• Monitor with pulse oximetry and arterial blood gases. 2

For Non-Hypoxemic Hypoxia

• Anemic hypoxia: Blood transfusion when hemoglobin <70 g/L in critically ill patients. 1, 2
• Stagnant hypoxia: Fluids, inotropes, vasopressors to improve cardiac output and tissue perfusion. 2
• Histotoxic hypoxia: Specific antidotes (e.g., for cyanide) and treatment of underlying sepsis. 2

Common Clinical Error

Focusing solely on oxygen therapy when SpO2 is normal but tissue hypoxia exists from anemic, stagnant, or histotoxic mechanisms will result in delayed appropriate treatment and worse outcomes. 2 Always assess lactate levels, hemoglobin, cardiac output, and clinical signs of tissue perfusion—not just oxygen saturation. 2