Hemorrhage is defined as the excess loss of blood due to rupture of blood vessels.
TYPES AND CAUSES OF HEMORRHAGE
Hemorrhage
occurs due to various reasons. Based on the cause, hemorrhage is classified
into five categories:
ACCIDENTAL HEMORRHAGE
Accidental
hemorrhage occurs in road accidents and industrial accidents, which are very
common in the
developed
and developing countries.
Accidental
hemorrhage is of two types:
i. Primary
hemorrhage, which occurs immediately after the accident
ii.
Secondary hemorrhage, which takes place some time (about few hours) after the
accident.
CAPILLARY HEMORRHAGE
Capillary
hemorrhage is the bleeding due to the rupture of blood vessels, particularly
capillaries. It is very
common in
brain (cerebral hemorrhage) and heart during cardiovascular
diseases. The rupture of the capillary is followed by spilling of blood into
the surrounding areas.
INTERNAL HEMORRHAGE
Internal
hemorrhage is the bleeding in viscera. It is caused by rupture of blood vessels
in the viscera. The
blood
accumulates in viscera.
POSTPARTUM HEMORRHAGE
Excess
bleeding that occurs immediately after labor (delivery of the baby) is called
postpartum hemorrhage. In some cases, it is very severe and leads to major complications.
HEMORRHAGE DUE TO
PREMATURE DETACHMENT OF PLACENTA
In some
cases, the placenta is detached from the uterus of mother before the due date
of delivery causing severe hemorrhage.
COMPENSATORY EFFECTS OF HEMORRHAGE
Many
effects are observed during and after hemorrhage. Effects are different in
acute hemorrhage and chronic hemorrhage.
Acute Hemorrhage
Acute
hemorrhage is the sudden loss of large quantity of blood. It occurs in conditions
like accidents. Decreased blood volume in acute hemorrhage causes hypovolemic shock.
Chronic Hemorrhage
Chronic
hemorrhage is the loss of blood either by internal or by external bleeding over
a long period of
time.
Internal bleeding occurs in conditions like ulcer. External bleeding occurs in
conditions like hemophilia and excess vaginal bleeding (menorrhagia). Chronic hemorrhage
produces different types of effects such as anemia.
Compensatory Effects
After
hemorrhage, series of compensatory reactions develop in the body to cope up
with the blood loss.
Compensatory
effects of hemorrhage are of two types.
A.
Immediate compensatory effects
B. Delayed
compensatory effects.
IMMEDIATE
COMPENSATORY EFFECTS OF HEMORRHAGE
1. On
Cardiovascular System
Reduced
blood volume after hemorrhage decreases venous return, ventricular filling and
cardiac output. In severe hemorrhage, there is fall in blood pressure also. However,
when blood loss is slow or less, the arterial blood pressure is not affected
much. If it is affected it is restored quickly.
During
mild hemorrhage
During
slow or mild hemorrhage when there is loss of a small amount of blood up to 350
to 500 mL the blood pressure decreases slightly and soon it returns back to normal.
Mechanism
involved in main tenance of blood pressure:
i. Usually
when arterial blood pressure increases, the carotid and aortic baroreceptors
are stimulated
and send
impulses to brain resulting in decrease in blood pressure. During hemorrhage
when the arterial
blood pres
sure falls, baroreceptors become inactivated and stop discharging impulses.
ii. This
increases the vasomotor tone leading to vasoconstriction. This type of reflex
vaso constriction
occurs in
all regions of the body except brain and heart.
iii.
Vasoconstriction results in increase in the peripheral resistance
iv. Loss
of blood also causes reflex constriction of veins
v.
Venoconstriction enhances the venous return, ventricular filling and stroke
volume
vi. Thus,
because of increased peripheral resistance and stroke volume the arterial blood
pressure
is restored
vii. One
more factor is involved in this mechanism. Vasoconstriction occurs in the organs
having
reservoir
function such as skin, liver and spleen. Blood from these reservoir organs is
directed into
systemic
circulation. This may compensate the volume of blood that is lost during
hemorrhage.
During
severe hemorrhage
When
hemorrhage is severe with loss of about 1,500 to 2,000 mL of blood, the arterial
blood pressure falls to a great extend. It is because of decreased venous
return and stroke volume.
In the
heart, the reflex tachycardia increases the quantity of metabolic products in
myocardium. These
metabolic
products cause coronary vasodilatation.
2. On Skin
Vasoconstriction
in skin, which occurs after hemorrhage decreases the cutaneous blood flow. It
increases the deoxygenation of blood and large quantity of reduced hemoglobin
is accumulated in cutaneous blood vessels. It results in greyish pallor color
of skin. Sometimes cyanosis develops in certain areas of
the body.
Skin also becomes cold due to less blood flow. Sweating is decreased.
3. On Tissue Fluid
Arteriolar
constriction decreases the capillary pressure. Therefore, tissue fluid enters
capillaries. It
helps to
compensate the blood loss. It also causes hemodilution.
4. On Kidneys
Constriction
of afferent and efferent arterioles of kidneys after hemorrhage decreases the
glomerular filtration rate (GFR) very much. Therefore, the urinary output decreases.
The blood level of nitrogenous substances, particularly urea, increases
resulting in uremia. Severe hemorrhage leads to fall in arterial blood pressure
and damage of renal tubules resulting in acute renal
failure.
5. On Renin
Secretion
Hypoxia
produced after blood loss increases secretion
of renin
from kidney and the subsequent formation angiotensin II. Angiotensin II helps
in restoring blood
pressure
by producing generalized vasoconstriction. It also increases release of
aldosterone from adrenal
cortex.
Aldosterone causes retention of sodium and this helps increasing the blood
pressure. Angiotensins III and IV are also involved in restoring the blood
pressure.
6. On Secretion of
Antidiuretic Hormone
Antidiuretic hormone
(ADH) is released in large quantities immediately
after the hemorrhage. It is probably due to increased osmolality of body fluid
by aldosterone induced sodium retention. ADH promotes water retention and helps
in restoring osmolality and volume of ECF.
7. On Secretion of
Catecholamines
Sympathetic
activity increases due to blood loss. It causes secretion of large quantities
of catecholamines, which are also involved in restoring blood pressure by the
vasoconstrictor effect.
8. On Respiration
Hemorrhage
causes stagnant hypoxia because of decrease in venous return, cardiac output
and velocity
of blood
flow. Hypoxia stimulates the chemoreceptors leading to increase in respiratory
rate. The catecholamines, which are secreted in large quantities due to
hemorrhage, increase the respiratory movements through reticular
activating system (RAS).
9. On Nervous
System
i. On brain
Though
hemorrhage causes vasoconstriction in many organs of the body, it causes
vasodilatation in brain. It is because of increased sympathetic
activity. However, the blood flow to brain is
not affected very much after hemorrhage because of autoregulation.
ii. On
reticular formation
Catecholamines
stimulate the RAS. It causes restlessness, anxiety and increased motor activity
after hemorrhage. The respiratory movements are also accelerated due to
stimulation of RAS.
iii. Fainting
When
hemorrhage is severe, cardiac output decreases and blood pressure falls. The
autoregulation in brain fails to cope up with the hypotension. So, the blood
flow to brain decreases resulting in fainting.
iv. Cerebral
ischemia
When the
blood flow to brain is severely affected due to hypoxia, ischemia of the brain
tissues develops within 5 minutes. It causes irreversible damage to brain tissues.
DELAYED COMPENSATORY
EFFECTS OF HEMORRHAGE
If
hemorrhage is not severe, some delayed compensatory reactions occur. These
reactions help to restore blood volume, blood pressure and blood flow to
different regions of the body.
Delayed
reactions are:
1.
Restoration of plasma volume
2.
Restoration of plasma proteins
3.
Restoration of red blood cell count and hemoglobin content.
1. Restoration of
Plasma Volume
During the
period of hemorrhage itself, tissue fluid starts entering the blood because of
low capillary pressure. So, the plasma volume increases. Because of increase in
plasma volume, hemodilution
occurs.
So, the concentration of plasma proteins and hemoglobin is low. Transport of
fluid from tissues is
continued
for long time after hemorrhage.
2. Restoration of
Plasma Proteins
The
reserve proteins stored in liver start mobilizing within few hours after
hemorrhage. Liver also starts
synthesizing
the plasma proteins. Restoration of plasma proteins occurs within 3 to 4 days.
Plasma proteins help to retain the fluid transported from tissues to blood.
3. Restoration of
Red Blood Cell Count and Hemoglobin Content
Hypoxia
that is developed after hemorrhage stimulates the secretion of erythropoietin
from kidney. Erythropoietin in turn stimulates red bone marrow causing erythropoiesis.
However, restoration of RBC count is a slow process. It takes about 4 to 6
weeks. Reticulocyte count increases in blood. Hemoglobin content also comes
back to normal level along with RBC count, if the diet contains adequate quantity
of iron and proteins.
0 Comments