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Abstract:
The study was made of the recent literature on controlled hypotension and its place in modern anaesthetic practice. The effects of the different techniques and drugs are outlined in this paper. The results of investigation revealed that the circulation of heart, brain, liver, and kidneys is able to tolerate a wide range of deviation of blood pressure. Hypotension induced by high doses of halothane alone, which used to be considered as an adequate measure, has recently been shown to cause such serious side-effects that it can no longer be recommended. Halothane lowers blood pressure almost exclusively by means of a reduction of the contractility of the heart muscle. Ganglionic blocking agents alone should not be used either because of their depressing effect on the heart; moreover their hypotensive effects are hard to control. The sole exception is trimetaphan but it produces other severe side-effects such as liberation of histamine. On the other hand ganglionic blocking agents combined with halothane can be recommended. The combined administration of these drugs allow an easy control of hypotension and the side effects are minimal. Only sodium-nitroprusside meets all the requirements of a hypotensive drug. It operates selectively in a peripheral vasoplegic manner without effecting the cerebral centres. Regarding the heart, no side-effect is known apart from tachycardia; cardiac output is not altered. The metabolism of sodium-nitroprusside requires precaution in dosage, as degradation takes place via the toxic compounds of cyanide. Therefore liver disease and disturbances in vitamin B12 utilisation are regarded as contraindications for the use of nitroprusside. That is also the reason why a maximum allowable dose of 10-15 gamma/kg body weight and minute should not be exceeded. Prophylactic administration of vitamin B 12a (hydroxocobalamin) should be considered in every case when nitroprusside is used.