Makindo Medical Notes

💉 Sodium Nitroprusside is a potent, fast-acting vasodilator used for short-term blood pressure control in critical care. ⚠️ Its use is limited by the risk of **cyanide accumulation** with prolonged infusion → requires expert supervision and careful monitoring. 👉 Always check the BNF link here before prescribing.

🧪 About

• Chemical formula: Na₂Fe(CN)₅NO·2H₂O.
• Highly photosensitive in solution → must be protected from light (wrap infusion bag/tubing).
• Used as an IV infusion only (never bolus).

⚙️ Mode of Action

• Direct relaxation of vascular smooth muscle → balanced arterial & venous dilatation.
• Reduces preload & afterload → rapid fall in BP and reduced cardiac workload.
• Onset within 1–2 minutes, duration short → needs continuous infusion & invasive BP monitoring.
• Tachyphylaxis may occur with prolonged use.

💊 Indications & Dosing

• 🚨 Hypertensive emergencies – immediate BP reduction.
• 💔 Acute LV failure / cardiogenic pulmonary oedema (specialist setting).
• 🔪 Aortic dissection (with beta-blocker e.g. labetalol to prevent reflex tachycardia).

Dosing

• Initial: 0.3–1.5 micrograms/kg/min, titrate slowly.
• Typical range: 0.5–8 micrograms/kg/min.
• Stop if no satisfactory response after 10 minutes.
• Heart failure: often lower fixed doses (10–200 micrograms/minute).
• ⚠️ Must be administered in ITU/CCU with invasive BP monitoring.
• Infusion must be protected from light.

🔗 Interactions

• Refer to BNF for detailed list.
• Other antihypertensives → risk of profound hypotension.
• Nitrates & PDE5 inhibitors → additive vasodilation.

🚫 Contraindications

• Severe aortic stenosis or hypertrophic cardiomyopathy (risk of worsening obstruction).
• Significant renal impairment (CKD, AKI) → impaired cyanide clearance.
• Severe vitamin B12 deficiency or Leber’s optic atrophy (risk of cyanide toxicity).

⚠️ Side Effects

• Excessive hypotension → syncope, organ hypoperfusion.
• Cyanide & thiocyanate toxicity with prolonged/high-dose infusion → confusion, seizures, lactic acidosis, arrhythmias.
• Reflex tachycardia (often countered by concurrent beta-blocker).

💡 Clinical Pearls

✔️ Always use invasive arterial line monitoring when infusing nitroprusside.
✔️ Keep infusion time short (hours, not days) → toxicity risk rises with duration.
✔️ In aortic dissection, combine with a beta-blocker to blunt reflex sympathetic drive.
✔️ Watch for unexplained metabolic acidosis or neurological changes → think cyanide toxicity.

📚 References

• BNF: Sodium Nitroprusside
• Goldman-Cecil Medicine, 26th ed. – Critical Care Pharmacology.
• European Society of Cardiology (ESC) Hypertension Guidelines 2018.