Sodium nitroprusside: theory and practice.

Sodium nitroprusside, by a peripheral vasodilator action, is a powerful hypotensive drug. In contrast to established agents, its hypotensive action is accompanied by an unchanged or augmented cardiac output. Intravenous administration of sodium nitroprusside rapidly produces a profound and controllable hypotension. Normotension is swiftly restored by ceasing to infuse the agent, and antidotes are unnecessary. Its attributes make it especially suitable for neurosurgical anaesthesia, and although free cyanide is liberated during biotransformation, side effects are virtually absent provided that dosage is reasonable. Special contraindications to its use are hypothyroidism and altered cobalamin metabolism.