2012
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Influential Citations
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Quality indicators
Journal
Drugs
Abstract
Sodium nitroprusside (SNP; 'Nipride') is a well established, potent, reliable antihypertensive agent of particular use during clinical anaesthesia, in the treatment of hypertensive emergencies, and as an aid to the management of severe intractable cardiac failure. This article reviews recent literature on the use and problems of sodium nitroprusside. When infused, the drug is capable of producing profound hypotension and many workers consider that direct arterial monitoring is mandatory. On withdrawal of the drug the arterial pressure always rises spontaneously and vasopressors are never required provided blood loss has been replaced. Overdosage with SNP is inevitably associated with rises in plasma and red cell cyanide and later with increases in plasma thiocyanate. During normal infusion these increases have no measurable adverse effects on the patient, but attempts to combat tachycardia and 'resistance' by infusion of the drug at high rates can result in total doses of sodium nitroprusside which will, in time, produce a dangerous rise in levels of plasma cyanide. The most probable explanation of 'resistance' to sodium nitroprusside can be explained by the baroreceptor mechanism, the main control mechanism for the maintenance of arterial blood pressure. Fall in arterial pressure decreases the activity of the baroreceptors, causing traffic of impulses up the glossopharyngeal and vagus nerves to the vasomotor and vagal centres leading to peripheral vasoconstriction, a decrease in vagal tone and a reflex tachycardia. This reflex tachycardia is well described and is a particular problem in young people but appears to be more troublesome with ganglion blockers than with sodium nitroprusside. In most cases this tachycardia is manageable. It can certainly beminimised by adoption of an anaesthetic technique which avoids anticholinergics and always includes intermittent positive pressure ventilation. If, despite this, tachycardia is still a problem the drug must not under any circumstances be 'pushed' but rather a small dose of a ~-adrenergic blocker, e.g. propranolol, given.