ICU: Nitroprusside infusion and toxicity

Dose: Start @ 0.5 mcg/kg/min and titrate to effect.
Usual dose: 3 mcg/kg/min
Max. dose: 8-10 mcg/kg/min (Rarely, need >5 mcg/kg/min)

Half-life: 10 min

Converted to cyanide in RBCs and tissue; Cyanide is converted in liver to thiocyanate. Thiocyanate is excreted in in urine.

Monitor for toxicity if:
1) > 4 mcg/kg/min for > 3 days
2) Liver dysfunction (Cyanide toxicity)
3) Renal dysfunction (Thiocyanate toxicity)

Monitoring parameters: HR, BP, pH (metabolic acidosis), Lactate level, Serum level of cyanide and thiocyanate

Cyanide toxicity:
Metabolic acidosis, Tachycardia, pink skin, decreased pulse, decreased reflexes, altered consciousness, coma, almond smell on breath, methemoglobinemia, dilated pupils
Normal: <> 2 mcg/ml
Potentially lethal: > 3 mcg/ml

CyanmetHb forms from the cyanide which is part of Nitroprusside molecular structure. This is more common in postop. cardiac patient because of availability of more Hb in plasma due to hemolysis during cardiopulmonary bypass. Antidote: Sodium thiosulphate or Sodium nitrite.

Thiocyanate toxicity:
Psychosis, blurred vision, confusion, weakness, tinnitus, seizures
Toxic: 35-100 mcg/ml
Fatal: > 200 mcg/ml

Source: Lexi-Comp's Pediatric Dosage Handbook 12th ed. (2005-6)

No comments: