Hypoxia

Hypoxia


Hypoxia is defined as an inadequate Oxygen supply to the body tissues.

Normal values : PO2 –  85 -100mm Hg Moderated hypoxia :  PO2 –  < 60mm Hg Serius hypoxia :  PO2 –  < 40mm Hg

Causes of Hypoxia
Hypoxia can be caused by an inadequate oxygenation of the blood in the lungs: deficiency of O2 in the atmosphere, hypoventilation (neuromuscular disorder);

Pulmonary disease: abnormal alveolar ventilation-perfusion ratio;

Venous-to-arterial shunts (right-to-left);

Inadequate O2 transport to tissues by the blood: anemia / abnormal hemoglobin, generalized/Localized circulatory deficiency;

Inadequate tissue ability to use the O2.

Types of Hypoxia
There are four different types of hypoxia:

Hypoxic Hypoxia: In which the partial pressure of Oxygen in arterial blood is reduced. Its causes can be a decrease of atmospheric O2, at high altitudes, but also some Pathophysiological Mechanisms, as for example: Hypoventilation, Diffusion Limitation, Physiological Shunts, Anatomical Shunts. In this type of Hypoxia, the arterial PO2 is decreased as well as the venous PO2.

Anemic Hypoxia: In which the partial pressure of Oxygen in blood is normal, but there is an insufficient or non-functional amount of heamoglobin. Can be caused by: a deficiency of essential nutrients (iron, B12 vitamin), blood loss, hemolytic anemia (cell cycle disease).

Stagnant ( Ischemic) Hypoxia: Is the insufficient O2 that reaches the tissues due to reduced blood flow. Its causes can be: Systemic (entire body) - heart failure; Local area - obstructed artery (arteriosclerosis).

Histotoxic Hypoxia: Is known by the disability of the cell to use O2. Its causes are: inactivation of certain metabolic enzymes, chemical poisons like alcohol and cyanide poisoning by inhibition of oxidative enzymes.