Sodium Nitroprusside

How it works

It releases nitric oxide, which activates guanylate cyclase to increase cyclic GMP, relaxing both arterial and venous smooth muscle and reducing preload and afterload.

Prescribing in practice

• Prolonged or high-rate infusion can cause cyanide and thiocyanate accumulation, so use the lowest effective rate, limit duration, and watch for unexplained metabolic acidosis.
• Its effect is rapid in onset and offset, mandating continuous intra-arterial blood pressure monitoring and titration via an infusion pump.
• The solution is light-sensitive and must be protected from light, with caution in renal or hepatic impairment which affects metabolite clearance.

Monitoring

Monitor blood pressure continuously, ideally via an arterial line, and watch acid-base status and for features of cyanide toxicity during prolonged use.

Counselling the patient

• Explain to the team that the infusion must be light-protected and delivered by pump with continuous arterial pressure monitoring.
• Note that unexplained acidosis or rising lactate may indicate cyanide accumulation and should prompt review.
• Highlight that blood pressure can change very quickly, so titration is in small steps.

Evidence & guidelines

Sodium nitroprusside is a long-established agent for hypertensive emergencies, with its use tempered by the recognised risk of cyanide toxicity on prolonged or high-dose infusion.