Download Causes and types

Shock
Shock is a clinical syndrome of circulatory failure characterized by:
• Low cardiac output.
• Hypotension.
• inadequate tissue perfusion
Causes and types:
Shock occurs as a result of many disorders, and according to the
underlying cause, four main types of shock can be identified.
1-Hypovolsemic shock
This occurs as a result of severe reduction of the blood volume. Its
manifestations are those of severe haemontage It is called cold shock
because the skin of the patient is cold due to severe cutaneous
vasoconstriction.
Causes and types:
1. Hemorrhagic shock (severe haernorrhage)
2. Traumatic shock (severe trauma): This may be complicated by
precp1tation of myoglobin (from the crushed muscles) in the renal
tubules resulting in renal shutdown, kidney damage and anuria (crush
syndrome)
3. Burn shock (extensive bums): It is a hypovolemic shock which follow
extensive burns it is mainly due to loss of large amounts of plasma from
the burned areas.
4. Surgical shock (major surgery): It is a hypovolemic shock which
follows surgical operation (it is due to external and or internal
hemorrhage)
5. Dehydration (e g in severe diarrhea) it is due to lass of large amount of
Na+ in the urine or feces with the loss of water leading again to
hypovolemic shock.
2-flistribntfre shock
This type of shock is caused by widespread vasodilation (VD)
which markedly increases the capacity of the vascular system. The blood
volume is normal but the cardiac output is maldistributed to different
organs where more blood goes to the inactive abdominal viscera, skeletal
muscles and skin and less blood goes to the active, vital organs especially
the heart and brain which become under-perfused its manifestations are
generally similar to those of hypovolemic shock, but the skin is warm due
to VD (hence the name warm shock). Examples:
Neurogenic shock
This is a distributive shock which occurs on receiving sudden,
shocking news strong emotions as extreme fear, grief or se ere pan in
these cases, shocking news may cause failure of the sympathetic tone i e
there is sudden withdrawal of the sympathetic vasomotor tone which
results in widespread vasodilation. The decrease in cerebral blood flow
leads to fainting (a= a prolonged syncope loss of consciousness due to
cerebral ischemia).
A rapid fall in the blood pressure (B.P) also occurs in neurogenic
shock in which the sympathetic tone is decreased, usually because of
upper spinal card damage or spinal anesthesia.
Anaphylactic shock:
This is a distributive shock caused by a severe allergic reaction to
an antigen to which the subject was previously exposed, and sensitized,
eg. an injection of penicillin. The resulting antigen-antibody reaction
causes the release of large amounts of histamine which produces massive
vasodilation.
Septic shock:
This is a distributive shock produced by the invasion of the blood
stream by bacteria or their toxins; especially the gram-negative bacteria
which release an endotoxin that stimulates the polymorph nuclear
leucocytes and tissue macrophages to secrete many VD cytokines
(especially interleukin-i. tumor necrosis factor (TNT)). These substances
produce massive vasodilation leading to shock.
3-Cardiogenic shock (Congested shock)
This occurs as a result of inadequate pumping action of the heart
(severe depression of myocardial contractility) which leads to reduction
of the cardiac output and arterial BP (systolic pressure fails below 80
mmHg, the central venous pressure (right atrial pressure) is elevated
above 18 mmHg (congestion).
Its manifestations are similar to those of hypovolemic shock plus
congestion of the lungs and viscera due to failure of’ the heart to pump all
the venous blood returned to it (hence the name, congested shock).
Causes:
1- Extensive myocardial infarction involving the left ventricle.
2- Acute myocarditis.
3. Heart failure.
4. Severe ventricular arrhythmia.
4-Obstructive shock
It is caused by marked restriction of the diastolic filling of the
ventricles, e.g. by pericardial tamponed (compression of. the heart by
accumulation of excess fluid or blood in the pericardial sac) or massive
pulmonary embolism. The cardiac output is markedly reduced leading to
hypotension and shock.
Causes:
(a) A large pneumothorax.
(b) Massive pulmonary embolism.
(c) A cardiac tumor.
Danger of shock.. How does it cause death?
Serve shock may be fatal if not rapidly and properly treated,
especially if becoming irreversible. Death occurs as a result of
development of multiple positive feedback cycles for death cycles), for
example:
• Hypotension → cerebral ischemia depression of the VCC → VU and
bradycardia → more hypotension (and so on till death occurs).
• Hypotension → myocardial ischemia → low cardiac output → more
hypotension. and so on till death occurs (cardiac damage may be so
severe that the cardiac output is not restored to normal even if the blood
volume is increased):
• A late cause of death is pulmonary damage due to pulmonary micro
embolism by thrombi formed by coagulant agents released from the
damaged cells (acute or adult respiratory distress syndrome, ARDS).
Fainting (syncope)
It is a sudden transient loss of consciousness. it usually results from
cerebral ischemia; it is often due to cardiovascular abnormalities
including either venous pooling or reduced cardiac output. A person ho
has fainted typically exhibits shallow breathing, a weak pulse, and low
blood pressure.
Etiology or Types:
1) Vasovagal syncope: due to hypotension produced as a result of sudden
vasodilation associated with bradcardia.
• Psychophysiological; this commonly occurs in strong emotions.
• Reduction in venous return; by the increased intrathoracic pressure, this
reduces the cardiac output leading to hypotension, like;
1. Micturition syncope: hypotension; in addition to reflex bradycardia
induced by. voiding urine.
2. Defecation syncope.
3. Cough syncope.
4. Valsalva maneuver.
2) Orthostatic syncope or hypotension: it means a rapid hypotension that
occurs on sudden standing. It is accompanied by dimness of vision,
dizziness arid even fainting. It results on failure of the baroreflex to
compensate for the sudden downward gravitational pull on the blood. On
standing from supine position, the effect of gravity leads to pooling of
blood in the lower part of the body → decrease in venous return →
decrease in cardiac output → fall in arterial blood pressure (Orthostatic
hypotension) → decreased cerebral blood flow → brain ischemiasyncope (Orthostatic syncope or fainting).. it may occur in normal
persons, in hypovolemic, idiopathic, and in patients with diseases that
damage the sympathetic nervous system e.g., diabetes. and syphilis, and
in primary autonomic insufficiency (diabetes; decreased production of
catecholamines due to Dopamine B-hydroxylase enzyme deficiency).
3) Carotide sinus syncope. carotide sinus syndrome.
4) Neurocardiogenic syncope; reduced cardiac output;
• syncope due to heart block or sinus arrest.
• syncope may also occur in severe arrhythmias (tachycardia more than
160 beat/minute or in bradycardia less than 40 beat/minute).
• Myocardial infarction with pump failure.
• Valve diseases (aortic stenosis. mitral stenosis).
• long QT syndrome.
• cardiomyopathy (HOCM),
• Congestive heart failure.
5) Deglutition syncope: due to VD and bradycardia induced by
swallowing.
6) Effort syncope: common in patients having aortic or pulmonary
stenosis.