1. HYPOXIA RESPIRATORY FAILURE
M. Tatar
Dept. of Pathophysiology

2. HYPOXIA hypoxemia anoxia ischemia

3. glucose
38 ATP
Krebs´s
cycle O2
CO2
H2O
glucose
2 ATP
lactate
pyruvate

4. The aim of oxygen transport
to preserve high PO2 gradient between capillaries and mitochondria
Q x Hb conc. x (SaO2 – SvO2) O2 c
circulation
respiration
erythropoiesis
microcirculation
Hb afinity to O2
ADP
VO2 m

5. Classification of hypoxia (1)
Hypotonic hypoxemic hypoxia
-  PaO2,  CaO2; Q . Hb . ( SaO2 – SvO2)
- carotid body stimulation, hyperventilation
- pulmonary hypertension in chronic form
- respiratory failure
2. Izotonic hypoxemic hypoxia
- normal PaO2,  CaO2; Q .  Hb . ( SaO2 – SvO2)
- chemoreceptors are not stimulated, lack of dyspnea
- anemia, carboxyhemoglobin

6. Hb concentration and CaO2 interrelationship
300
100
polycythemia
Hb = 20
200
100
normal
Hb = 15
CaO2, ml/l
150
SaO2, %
100
anemia
Hb = 10
PaO2 , mmHg

7. Classification of hypoxia (2)
3. Hypoextractive hypoxia
- increased Hb afinity to O2
- Q . Hb . (SaO2 –  SvO2)
100
released O2
SaO2, % 50
pH = 7,4; t = 37 °C
pH  7,4; t  37 °C
PaO2, kPa

8. Classification of hypoxia 3
4. Hypocirculatory hypoxia
-  Q . Hb . (SaO2 – SvO2)
- ischemic, congestive; local, general
5. Overutilization hypoxia
-  demand of tissues for O2 excesses the available supply
- angina pectoris, epilepsy (fatigue and cerebral depression)
6. Histotoxic hypoxia
- disturbed ATP production, blocked oxidative phosphorylation
- Q . Hb . (SaO2 –  SvO2)
- cyanide

9. Respiratory failure - definition
Syndrome characterized by disturbed exchange of oxygen and carbon dioxide in lung
Consequences: PaO2  60 mmHg (8.0 kPa) with or without
PaCO2 > 50 mmHg (6.7 kPa)
- under resting condition
- breathing atmospheric air at sea level
Classification:
1. Hypoxemic (hypoxemia with normal or  PaCO2)
2. Hypercapnic (hypoxemia and hypercapnia)

10. Respiratory failure
Factors determining oxygenation and ventilation are different
PaCO2 must be regarded as a function of the overall ventilation of the entire lung, without regard to local inequalities of distribution of ventilation and perfusion
PaO2, on the other hand, depends not only on the amount of alveolar ventilation but also on the matching of ventilation and perfusion

11. Respiratory failure
Mechanisms responsible for gas exchange disturbances
A. intrinsic lung disorders (airways, lung parenchyma)
1. Ventilation/perfusion (V´/Q´) mismatch
2. Venous admixture
3. Diffusion impairment
B. extrinsic lung disorders (respiratory centre, nerve
pathways, respiratory muscles, thoracic cage, pleural
space)
1. Alveolar hypoventilation (overall)

13.  ventilatory drive PaO2 PaCO2 chemoreceptors SaO2 100 40 50 120 30
70%
chemoreceptors
SaO2
100%
hypoxemia
normocapnia
hypoxemia
hypercapnia

18. 2. compartments with low V´/Q´ ratio
Respiratory failure
Mechanisms of hypoxemia
1. alveolar hypoventilation
2. compartments with low V´/Q´ ratio
3. right-to-left shunting of blood in
compartments with zero V´/Q´ratio
4. diffusion impairment due to thickening of the
alveolar-capillary membrane

19. Diffusion impairment – oxygen saturation of arterial blood
normal
PcO2 12
impaired
kPa
exercise
rest
PvO2 4
0.8 s
Er contact time with A-c membrane

20. Respiratory failure
Mechanisms enhancing hypoxemia
Pure oxygen breathing:
 hypoxic pulmonary vasoconstriction
resorptive atelectasis ( PAN2,  resorption of O2)
 central inspiratory drive

21. Mechanisms of hypercapnia
Respiratory failure
Mechanisms of hypercapnia
1. overall alveolar hypoventilation
2. critical amount of the compartments with low
V´/Q´ ratio
overall ventilation must increase to maintain effective
alveolar ventilation (normal CO2 exchange)
limits of effective alveolar ventilation:
 work of breathing
respiratory muscle fatigue
 dead space ventilation