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Introduction

Hypoxemia, hypoxia, anemia, and ischemia are related, yet distinct processes:

  • Hypoxemia:  Low dissolved oxygen (O2) content of arterial blood, commonly defined as an arterial partial pressure of O2 (PaO2) <60 mm Hg.  Example:  parenchymal lung disease.
  • Hypoxia:  Low O2 content at the end-organ and tissue level.  It can be caused by hypoxemia, anemia, or ischemia.  Prolonged hypoxia typically results in tissue necrosis.  Example:  myocardial infarction.
  • Anemia:  Low number of circulating red blood cells (and therefore, hemoglobin content) in arterial blood.  Example:  iron deficiency.
  • Ischemia:  Low perfusion of end-organs and tissues, resulting in decreased O2 and other nutrients (eg, glucose).  Example:  arterial thrombosis.

This article discusses the mechanisms, pathophysiology, and evaluation of hypoxemia.

Normal oxygenation

Normal oxygenation requires 3 elements:

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