1. Physiology of hypoxia

2. Definition
▪ Reduced oxygen supply to the tissues

3. Classification
▪ Reduced oxygen tension of arterial blood – Hypoxic hypoxia
▪ Decreased oxygen carrying capacity of the blood – anemic hypoxia
▪ Decreased rate of blood flow to the tissues – stagnant hypoxia
▪ Decreased utilization of oxygen by tissues – histotoxic hypoxia

4. But first
▪ Arterial Po2
▪ Oxygen carrying capacity of blood (Hb value )
▪ A –V difference of Po2
▪ Percentage saturation of hemoglobin SaO2

5. Hypoxic hypoxia
▪ Decreased oxygen tension in blood
▪ Decreased O2 saturation of blood
▪ O2 carrying capacity of blood is normal
▪ Blood flow to the tissues normal
▪ Tissue utilization is normal
▪ A –V Po2 difference is low

6. Causes
▪ Low oxygen tension of inspire air
– High altitude
– Closed spaces
– Artificial gas breathing
▪ Hypoventilation
– Obstruction to respiratory passages
– Decreased lung compliance
– Paralysis of respiratory muscles
– Respiratory depression
▪ Reduced diffusion of O2 across respiratory membrane
– Emphysema , pulmonary edema , fibrosis

7. Anemic hypoxia
▪ Basic problem is decreased oxygen carrying capacity of blood
▪ Causes
– Anemia – bone marrow depression
– CO poisoning
– Met-haemoglobinemia

8. Characteristic features
▪ Arterial Po2 is normal
▪ O2 carrying capacity of blood is reduced ( SaO2 reduced)
▪ A –V difference is normal
▪ Normal tissue utilization

9. 2,3 DBG significance
▪ Increases O2 delivery to tissues
▪ Hbo2 + 2, 3 DBG Hb 2, 3 DBG + O2

10. Stagnant hypoxia
▪ Problem – decreased blood flow to tissues (stagnation)
▪ Normal Po2 , SaO2 , Hb , normal tissues
▪ Causes – generalized , localized
– Shock , CHF
– Thrombosis , embolism, atherosclerosis

11. Characteristic Features
▪ Normal pO2
▪ Normal SaO2
▪ A –V pO2 is high than normal

12. Histotoxic Hypoxia
▪ Problem with tissues
▪ Tissues not able to use the oxygen
▪ Inhibition of cellular respiration (ETC) by poisons
▪ Cyanide , sulphide poisoning
▪ Normal pO2
▪ SaO2 normal
▪ A –V difference is nil

13. Effects of hypoxia
▪ Hypoxia mainly affects CNS , specially the higher centers
▪ Fulminant hypoxia , acute hypoxia , chronic hypoxia
▪ Effects depends on the severity , duration and type , and
compensatory mech of body

14. Important Symptoms And Signs
▪ Cyanosis
▪ Tachycardia
▪ Tachypnoea
▪ Acute hypoxia resembles alcohol intoxication
▪ Anaerobic glycolysis
▪ Metabolic acidosis with respiratory alkalosis
▪ Angiogenisis
▪ Polycythemia
▪ Pulmonary hypertension