8.2 Hypoxia.ppt

Controls on natural planning

1. Hypoxia

2. Definitions
Hypoxia :
Hypoxia is defined as lack of oxygen at tissue
level.
Anoxia :
Anoxia is defined as complete absence of
oxygen in the tissues

3. Types of hypoxia
A.Hypoxic hypoxia
B.Anaemic hypoxia
C.Stagnant(ischaemic) hypoxia
D.Histotoxic hypoxia

4. A. Hypoxic hypoxia
•It is characterized by low arterial pO
2when oxygen
carrying capacity of blood and rate of blood flow to
tissues are normal or elevated
•It is characterisedby
i.Low arterial pO
2
ii.Low arterial O
2content
iii.Low arterial % O
2 saturation of haemoglobin
iv.Low A-V pO
2difference

5. Hypoxic hypoxia(contd.)
Causes:
1)Low pO
2of inspired air
2)Decreased pulmonary ventilation
3)Defect in exchange of gases
4)Venous arterial shunts

6. B.Anaemic hypoxia
In anaemic hypoxia arterial pO
2is normal but the
amount of haemoglobin available to carry oxygen is
reduced.
Causes :
i.Anemia
ii.Haemorrhage
iii.Conversion of haemoglobin to some abnormal form

7. Anaemic hypoxia(contd.)
•Characterized by:
i.Normal arterial pO
2
ii.arterial O
2content moderately reduced
iii.A-V pO
2difference is normal

8. C. Stagnant(ischemic) Hypoxia
Bloodflowtothetissueissolowthatadequateoxygen
isnotdeliveredtothemdespitenormalarterialpO
2
andhaemoglobinconcentration
Causes:
i.Circulatoryfailure
ii.Haemorrhageviabaroreceptorsleadingtoreflex
vasoconstriction

9. Stagnant hypoxia (contd.)
Characterized by:
i.Normal arterial pO
2
ii.Normal arterial O
2content
iii.normal arterial % O
2saturation of haemoglobin
iv.A-V difference more than normal

10. D.Histotoxic hypoxia
•Amount of oxygen delivered to the tissues is adequate
but because of the action of toxic agents the tissues
cannot make use of the oxygen supplied to them.
•Cause :Cyanide poisoningcausing damage to
enzyme cytochrome oxidase.
•Characterized by:
i.Normal pO
2
ii.No difference in O
2content of arterial and venous
blood.
iii.A-V pO
2difference is less than normal

11. Clinical features of hypoxia
1)Hyperventilation is seen in all types of hypoxia except
anemic hypoxia
2)In all types of hypoxia the first symptoms are like that of
alcohol overdose(drowsiness, depression/excitement,
emotional outburst)
If oxygen saturation of haemoglobin falls below 60% there
unconsciousness within 20 seconds, causing death in 4-5
minutes.
3)Severe hypoxia( except anaemic) causes increase in heart rate
and systemic blood pressure.
4)Associated symptoms-nausea, vomiting and anorexia

12. Treatment of hypoxia
1.Treatment of the underlying cause-depending upon
the type of hypoxia
2.Oxygen therapy-
i.Inhalation of 100% pure oxygen
ii.Hyperbaric oxygen therapy

14. CYANOSIS
Bluish discoloration of skin and/or mucus membrane
due to the presence of at least 5gm of reduced
haemoglobin per 100ml of blood in capillaries.
Sites to be examined:
i.Mucus membrane of undersurface of tongue
ii.Lips
iii.Ear lobes
iv.Nail beds
v.Tip of nose

15. Types of cyanosis:
1.Centralcyanosis-Duetoacirculatoryorventilatory
problemthatleadstopoorbloodoxygenationinthelungs.
Itdevelopswhenarterialsaturationofbloodwithoxygenis
≤85%.Cyanosismaynotbedetecteduntilsaturationis75%
indark-skinnedindividuals
2.Peripheralcyanosis-Duetoinadequatecirculation.
Allfactorscontributingtocentralcyanosiscanalsocause
peripheralsymptomstoappear,howeverperipheralcyanosis
canbeobservedwithouttherebeingheartorlungfailures.

16. Causes of cyanosis
1.Hypoxic hypoxia
2.Stagnant hypoxia
3.Polycythemia
4.Exposure to mild cold( approx 20
0
C) produces
cyanosis while exposure to severe cold (appprox.
10
0
C or below) does not produce cyanosis.

17. Cheyne-Stokes respiration
•Cheyne-Stokes respiration is also known as
periodic respiration, with cycles of respiration
that are increasingly deeper then shallower
with possible periods of apnoea. Typically,
over a period of 1 minute, a 10-20 second
episode of apnoea or hypopnoea occurs
followed by respirations of increasing depth
and frequency. The cycle then repeats itself.

18. Causes of Cheyne-Stokes respiration
•Causes include:
–Brainstem lesions: cerebrovascular event
–Encephalitis
–Raised intracranial pressure
–Heart failure
–Chronic pulmonary oedema
–Altitude sickness

19. Pathophysiology
•Instability of respiratory control underpins the
development of Cheyne-Stokes respiration
and results from hyperventilation, prolonged
circulation time, and reduced blood gas
buffering capacity