Pathophysiology of hypoxia with clinical relevance

1. Pathophysiology
of hypoxia and
cyanosis
Dr. Dinesh Veera
(MBBS, MSc Medical Physiology)
AIMST University

2. Learning Outcomes
Describe the characteristic features of different types of hypoxia.
Describe the types and effects of cyanosis.

3. Definitions
Hypoxia is defined as a
decrease in O2
delivery to, or
utilization by, the
tissues
Hypoxemia is defined
as a decrease in
arterial PO2.

4. Cause of hypoxia

5. 1. Inadequate oxygenation of the blood in the lungs because of
extrinsic reasons
a. Deficiency of oxygen in the atmosphere
b. Hypoventilation (neuromuscular disorders)

6. 2. Pulmonary disease
a. Hypoventilation caused by increased airway resistance or decreased
pulmonary compliance
b. Abnormal alveolar ventilation-perfusion ratio
c. Diminished respiratory membrane diffusion

7. • 3. Venous-to-arterial shunts
(“right-to-left” cardiac shunts)

8. • 4. Inadequate oxygen transport to the tissues by the blood
a. Anemia or abnormal hemoglobin
b. General circulatory deficiency
c. Localized circulatory deficiency (peripheral, cerebral, coronary
vessels)
d. Tissue edema

9. • 5. Inadequate tissue capability of using oxygen
a. Poisoning of cellular oxidation enzymes
b. Diminished cellular metabolic capacity for using oxygen, because of
toxicity, vitamin deficiency, or other factors

11. Types and Hypoxia

12. I-Hypoxic or arterial hypoxia
Reduced arterial PO2 it can be due to
• Alveolar hypoventilation
• Diffusion abnormalities
• Right to left shunt
• Ventilation-perfusion imbalance ( including
increased physiological dead space and
physiological shunt).

13. II-Anemic hypoxia
• It is caused by reduction in the oxygen carrying capacity
of the blood, due to decreased amount of Hb or
abnormal type of Hb which is unable to carry oxygen.
• The PO2 and % Hb-O2 is normal.
Causes:
1- Anemia
2-Abnormal Hb e.g met hemoglobin, carboxyhemoglobin.
Dr.Aida Korish 13

14. III-Stagnant hypoxia:
• Caused by reduced blood flow through the tissues,
so more and more oxygen is extracted from the blood,
and due to slow circulation less oxygen is carried by the
blood at the lung , leading to hypoxia.
• Causes:
• 1-General slowing of the circulation, as in heart failure
and shock
• 2-Local slowing e.g vasoconstriction, cold, arterial wall
spasm.
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15. IV- Histiotoxic hypoxia
• This is inability of the tissues to use oxygen due to
inhibition of the oxidative enzyme activity
• e.g cyanide poisoning causing blockade of the
cytochrome oxidase activity

16. CYANOSIS:
• Definition: Bluish discoloration of skin & mucus membrane
• excessive amounts of deoxygenated hemoglobin in the skin blood
vessels, especially in the capillaries.
• This deoxygenated hemoglobin has an intense dark blue– purple color
that is transmitted through the skin.
• In general, definite cyanosis appears whenever the arterial blood
contains more than 5 grams of deoxygenated hemoglobin in each 100
milliliters of blood

17. Types of Cyanosis:
1. Peripheral:
• Seen on:
• exposure to moderate cold &
• in case of stagnant hypoxia.
• Seen in:
• fingers,
• outer surface of lips.
• Arterial PO2 remains normal.

18. Types of Cyanosis:
2. Central:
• Seen in :
• case of Congenital heart diseases
&
• chronic lung disease.
• Mostly Arterial PO2 is below
normal (due to hypoxic hypoxia).

19. Conditions in which Cyanosis
does not occur:
• Severe anemia (less than 5 gram deoxy Hb/dl)
• CO poisoning (masked due to cherry red complexion)
• Met-Hemoglobinemia (chocolate brown discoloration)

20. References
Physiology, Linda
S. Costanzo 6th
Edition
Guyton and Hall
14th Edition