- Absence of oxygen.
- A pathological deficiency of oxygen, especially hypoxia.
- a physiological state in which insufficient oxygen reaches the tissues of the body, especially when of sufficient severity to cause permanent damage.
- A condition in which a tissue or environment is severely or totally deprived of <xref>oxygen</xref>, severe <xref>hypoxia</xref>.
- severe hypoxia; absence of oxygen in inspired gases or in arterial blood or in the tissues