hypoxia and Classify o hypoxia:
§
Definition:
It may be defined as lack of supply of oxygen to tissues below the normal
level.
§
Classification:
A. Hypoxic hypoxia: There is
defective oxygenation of blood in lungs, hence O2 in tissue is also
below the normal level. This may occur in the following conditions-
1. The
atmosphere may have low O2 tension.
2. The
atmosphere may be polluted with irrespirable gases, CO1, CO2
(here the person is normal)
3. There
may be some block in lung tissue & alveoli as may occur in pneumonia &
pulmonary oedema.
4. If
the pt. has long standing emphysema, the ventilatory capacity is lowered.
5. There
may be tumor in the bronchus obstructing air. There may be obstruction in
larynx either intramural or extramural. There may be external pressure in the
neck constricting the airway like hanging, strangulation, throattling.
The person may
be drowned in water, milk, inspiring not air but liquid. In all above cases,
less O2 is refused in the body.
B. Anaemic hypoxia: here reduced O2
capacity of blood owing to lack of RBC or Hb which may be inadequate or
abnormal. For example- CO poisoning, massive or severe haemorrhage.
C. Stagnant hypoxia: There is
inadequate circulation of blood where the circulation is very much low.
example- tight ligature in snake bite. It may be local where there is a venous
& arterial ligature. It may be generalized due to central cause like heart
failure.
D. Histotoxic hypoxia: In this
type, even the O2 supply is adequate & reaches the tissue, yet
the tissue that will take O2 be in defective as it is poisoned by
some mechanism.
In
other words, there is depression in the oxidative process in the tissue. This
can be subdivided into following 4 types:
1. Extraceellular: O2 enzyme
system of body is poisoned, eg. cyanide poisoning.
2. Intracellular: Decrease in cell
membrane permeability thereby O2 can’t gain access to the cell. eg.
anaesthetics like chloroform, ether etc.
3. Metabolic: The end product of
metabolism can’t be removed thus preventing furthur metabolism. eg. uraemia, CO2
poisoning.
4. Substrate: Not sufficient food
staff for efficient metabolism.
Asphyxia the types with causes of asphyxia.
§
Definition:
It may be defined as a condition in which the supply of O2 to the
blood & tissues has been reduced appreciable below the normal working level
as a result of some interference with respiration causing in consciousness or
death.
§
Types:
1. Mechanical:
Air-passages are blocked mechanically. eg.
i. Closure of external respiratory orifices as
by closing nose & mouth with hand or cloth
or by filling these openings with mud or other substances as in smothering.
ii. Closure of air passages by external pressure
on the neck, as in hanging, strangulation
throttling.
iii. Chocking.
iv. Drowning.
- Bronchitis.
- Acute edema of glottis.
- Laryngeal spasm.
- Tumors & abscess.
- Paralysis of respiratory muscles (result from acute poliomyelitis).
3. Toxic: Poisonous substances
prevent the use of O2.
- Capacity of Hb to bind O2 is reduced, eg. poisoning by CO.
- Enzymatic process by which O2 in blood is utilized by the tissues are blocked, eg. cyanides.
- Respiratory centers may be paralysed in poisoning by opium, barbiturate, strychnine.
- Respiratory muscles may be paralysed by poisoning by gelsemium.
4. Environmental:
a. O2
in inspired air: enclosed places, trapping in a disused refrigerator or trunk.
b. Exposure
to irrespirable gases in the atmosphere: sewer gas, CO, CO2.
5. Traumatic:
- Pulmonary embolism from femoral vein thrombosis due to lower limb injury.
- Pulmonary fat embolism from fracture of long bones.
- Pulmonary air embolism from an incised wound of internal jugular vein.
- Bilateral pneumothorax from injuries to the chest wall or lungs.
6. Positional: Results from
forcible flexion of the neck on the chest.
7. Iatrogenic: is associated with
anesthesia.
