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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. |