Hypoxia & Cyanosis physiology of respiration 1.pdf

Physiology

1. HYPOXIA & CYANOSIS

2. Hypoxia
•Reduced oxygen
delivery to a tissue
(tissues)

3. Factors that determine amount of
O2
1.{O2} in blood
2.Blood flow
3.Ability of the tissue to extract O2
Decrease in any of these will cause
hypoxia if the other two are kept
constant

4. {O2} in blood
•Determined by:
1.Hemoglobin concentration
2.Ability of hemoglobin to carry O2
3.PaO2
dissolved O2)
Decrease in any of these will decrease {O2}
if the other two are kept constant

5. Hypoxias due to low {O2} in
blood
•Hypoxic Hypoxia
•Anemic Hypoxia

6. Hypoxic hypoxia (hypoxemia)
•Due to low PaO2
•Caused by reduced oxygenation of
blood in the lungs

7. Causes of hypoxic hypoxia
 O2
alveolar ventilation (hypoventilation)
O2
Normal alveolar PO2

pulmonary edema
Ventilation perfusion inequality
Shunting of venous blood to arterial blood
(veno-arterial shunts)

8. Characteristics of hypoxic hypoxia
•Low {O2} in blood
•Low percent saturation
•Low PaO2

9. Anemic hypoxia
•Due to:
–Low hemoglobin concentration
(anemia)
–Abnormal hemoglobin
(methemoglobin)
–Occupied hemoglobin (carbon
monoxide)

10. Characteristics of anemic hypoxia
•Low {O2} in blood
•Normal PO2
•Percent saturation
–Normal in anaemia
–Low if haemoglobin is occupied by
carbon monoxide
–Low if hemoglobin is abnormal

11. Hypoxia due to low blood flow
•Generalized
–Heart failure
–shock
•Localized
–Venous obstruction
–Arterial obstruction
Called stagnant hypoxia

12. Characteristics of stagnant hypoxia
•Normal PaO2
•Normal percent saturation
•Normal {O2} in arterial blood
All these are lower than normal in
venous blood

13. Hypoxia due to inability of tissue to
extract O2
•Called histotoxic hypoxia
•Due to
–Toxins (cyanide poisoning)

14. Characteristics of histotoxic hypoxia
•Normal PaO2
•Normal percent saturation
•Normal {O2} in arterial blood
All these are higher than normal in
venous blood

15. Oxygen therapy is effective in:
•Some hypoxic hypoxias;
–Hypoventilation
–Thick respiratory membrane
–Ventilation perfusion inequality
•Some anaemic hypoxias;
–CO poisoning;
•Hyperbaric O2

16. Oxygen therapy is not very effective
in:
•Some hypoxic hpoxias
–Veno-arterial shunt
•Some anaemic hypoxias
–Anaemia
–Abnormal haemoglobin
•Stagnat hypoxia
•Histotoxic hypoxia

17. Cyanosis
•Blue coloration of skin/mucous
membranes
•Due to high {reduced Hb}:
–5g/dl
•Occurs in:
–Hypoxic hypoxia
–Stagnant hypoxia

18. Cyanosis
•Types:
–Peripheral
•Localized stagnant hypoxia
–Tips of finger (cold exposure)
–Central
•Hypoxic hypoxia
•Generalized stagnant hypoxia
•Does not occur in severe anemia