الفهرس 
Material and methodsOnly 14 pages are availabe for public view
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Abstract
Bleeding during surgery is one of the major problems both to
It can hamper the
the surgeons and to the anaesthetist.
surgeon’s work. make dissection more difficult and prolong the
durat,ion of operation. so. the need for some means of controlling
blood loss during surgical procedures was important in the minds
of those surgeons in the 1930 sl Arteriotomy with consequent
reduction in blood volume and vasoconstriction was tried by some;
others used spinal anaesthesia with its
resultant peripheral
pooling of blood in the dilated distal circulatory bed, with
consequent reduction of blood loss in the operative field .
.Ganglion blockers were then used for production of induced
hypotension.
concentrated on the use of halothane either alone or as adjunct
In recent years methods of induced hypotension have
to other hypotensive agents
Then sodium nitroprusside was used
for production of hypotension.
Deliberate hypotension may be induced by many different
drugs but the fundamental action of each is one of two mechanism
1) A reduction in cardiac output.
2) Change in the peripheral circulation.
The extent of controlled hypotension plUS the application of
the principles for maintaining tissue oxygenation is a measure of
the safety of the technique.
In most instances the induction of
hypotension is accompanied by postural manipUlations to divert
the blood from specified areas.
The methods of induced hypotension during surgery are either
1) Pharmacological blockade, it is based on ganglion block by
pentolinium, trimetaphan, and assisted by such drugs as halothane
to which may be added the effects of beta-adrenergic blockers as
propranolol. practolol or labetalol, head up tilt, IPPV and
positive end expiratory pressure (PEEP). The principle is to
reduce cirCUlatory homeostatic reflexes to such a degree that,
when challenged with head up tilt and PEEP they are no longer
able to maintain normal blood pressure. Advantages of this method
are the hypotension can be reversed quickly by change in PEEPand
reducing the head up tilt, and the reduction of angiotensin and
plasma renin activity (which allow an easier and safer control of
pressure).
2) Direct-acting vasodilators (SNP and nitroglycerine, ATP). SNP
rapidly gained acceptance as a major hypotensive agent, its
rapid, transient and potent action making it the agent of choice
in many circumstances.
3) Combined- use of haemodilution and hypotension, since
deliberate hypotension can decrease blood loss and since acute
normovolaemic haemodilution minimises the need for homologous
blood, it seems logical that the combined use of both techniques
should be more advantageous.
~lg ffigin1nd1aat1Qn~ lOr induced hypotension are :_
1) Blood loss may be so minimised that transfusion may be avoided
2) \Vhere severe haemorrhage is likely to obscure the field of
operation. This makes the dissection difficult and so prevents
the accurate total removal of dangerous lesion such as a
parotid tumour or a large haemangioma.
3) \’lherethere is an undue rLsk of t .
L pos operat~ve haematoma. So
,induced hypotension is indicated in the following types of
operation, brain tumours, aneurysm, coarctation of aorta.
vascular tumours, plastic surgery. and operation on internal
ear, nos~, and eyes.
Inlluced hypotension is contraindicated in the following
conditions ’-
1) Disease states, as severe cardiac diseases. arteriosclerosis.
obstructive lung diseases. poor renal or hepatic functions or
Addison’s disease.
2) Clinical conditions as uncorrected anaemia, shock. or
pr~operative haemorrhage, hypovolaemia.
3) Technical difficulties, inadequate skill.
Complications of induced hypotension are
Cerebral thrombosis. thrombosis of the central artery of
the retina. leading to unilateral blindness, coronary thrombosis,
oliguria and reactionary haemorrhage.
The size of risk during controlled hypotensive anaesthesia
depends on the state of patient. vascular tree, the degree of
hypotension attained and careful blood pressure, ECG. EEG
monitoring.