QS Study

Definition: Hypoxia is Oxygen deficiency at the tissue level. The brain depends on the blood to provide it with a regular supply of oxygen. Thus disruptions to any element of the body that plays a function in blood or oxygen supply can lead to hypoxia.

Classification

Traditionally, hypoxia has been decided into four types:

(A) Hypoxic hypoxia: (anoxic anoxia) – Hypoxia due to inadequate oxygenation of blood in the lungs because of extrinsic reasons or pulmonary disease. This refers to hypoxia resulting from an inadequate saturation of blood oxygen due to a reduced supply of oxygen in the air, decreased lung ventilation, or respiratory disease.

Cause

(a) Inadequate oxygenation of the blood in the lung because of intrinsic reasons –

  • Deficiency of oxygen in the Atmosphere,
  • Hypoventilation (neuromuscular disorder)

(b) Pulmonary disease

  • Hypoventilation due to increased airway resistance or decreased pulmonary compliance.
  • Diminished respiratory membrane diffusion.

(c) Venous to arterial shunt (right to left cardiac shunt)

Oxygen-therapy in hypoxic hypoxia –

  • In atmospheric hypoxia – 100% effective.
  • In hypoventilation hypoxia – 100% is extremely beneficial.
  • In hypoxia caused by impaired alveolar membrane diffusion – highly effective.
  • In physiologic shunt – Much less value.

 

(B) Anaemic hypoxia – In which the arterial PO2 is normal but the amount of haemoglobin available to carry Oxygen is reduced. This refers to when the capacity of the blood to carry oxygen is reduced and inadequate levels of oxygen are therefore circulated around the body.

Cause

(a) ↓ Hb (Anaemia)

(b) Carbon monoxide poisoning

(c) Abnormal haemoglobin.

Oxygen therapy – In anamic hypoxia oxygen therapy is of much less value.

 

(C) Stagnant or ischemic hypoxia – When oxygen tension, Hb is normal but the amount of oxygen reaching the tissue is inadequate, this hypoxia is called stagnant hypoxia. Heart attack, heart failure, or cardiac arrest, for example, can slow the circulation of blood meaning inadequate oxygen is delivered to important tissues and organs.

Cause

Generalized deficiency

  • Cardiac output
  • Impaired venous return
  • Congestive cardiac failure.

Localized circulatory defect

  • Blood flow to the organ.
  • Haemorrhage and shock etc.

Oxygen therapy – Oxygen therapy is of much less value, because of atherosclerosis, or vasoconstriction.

 

(D) Histotoxic hypoxia – In which the amount of oxygen delivered to a tissue is adequate but because of the action of a toxic agent, the tissue or cells cannot make use of the oxygen supplied to them. This may occur with the overuse of alcohol or drugs and is also seen in cyanide poisoning.

Cause

  • Poisoning with KCN which paralyzed the cytochrome oxidase.
  • Narcotics
  • Lack of the oxidative enzyme
  • Vitamin deficiency (Beri beri)

Oxygen therapy – O2 therapy is very limited value.