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Life in the Fast Lane • LITFL • Medical Blog

Emergency medicine and critical care medical education blog

Critical Care Compendium | Sodium Nitroprusside

Sodium Nitroprusside

by Chris Nickson, Last updated April 26, 2013

CLASS

  • an inorganic complex

MECHANISM OF ACTION

  • vasodiator & hypotension
  • dilates both resistance & capacitance vessels by direction on vascular smooth muscle.
  • acts by interacting with sulphdryl groups in smooth muscle membrane & preventing Ca2+ influx necessary for initiation of contraction

PHARMACEUTICS

  • solution: 10mg/mL
  • must be diluted before administration
  • must be protected from light
  • IV

DOSE

  • 0.5 – 4mcg/kg/min
  • titrated according to response
  • need art line
  • onset: immediate

Indications

(1) hypertensive crises
(2) aortic dissection
(3) LVF
(4) produce hypotension during surgery

Adverse Effects

  • reversible decrease in PaO2 from decrease in hypoxic pulmonary vasoconstriction
  • cerebral vasodilation -> increase in ICP
  • increase in catecholamine
  • increase in renin
  • lactic acidosis may occur
  • toxicity from cyanide production

PHARMACOKINETICS

  • Absorption – n/a
  • Distribution – confined to the plasma
  • Metabolism

(1) reaction with sulphdryl groups on amino acids in plasma
(2) rapid, non-enzymatic hydrolysis within RBC’s

  • 5 cyanide ions are produced by the degradation of each molecule of Na nitroprusside
  • 1 reacts with metHb -> cyanometHb
  • 3 react with thiosulphate -> thiocyanate (catalysed by hepatic rhodanese)
  • 1 reacts with hydoxy-cobalamin -> forms cyanocobalamin (vitamin B12)
  • Elimination – thiocyanate & cyanocobalamin -> urine, t1/2 of thiocyanate = 3 days

EVIDENCE

Major issue – liability to cyanide toxicity

  • risk increased by hypothermia, malnutrition, vitamin B12 deficiency, hepatic or renal impairment
  • related to rate of infusion rather than total dose.
  • cyanide ion combines with cytochrome C -> impairment of aerobic metabolism -> metabolic lactic acidosis
  • signs:
  • tachycardia
  • dysrhythmias
  • hyperventilation
  • sweating
  • treatment:
  • stop SNP infusion
  • supportive measures
  • sodium thiosulphate
  • dicobalt edentate
  • sodium nitrite

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About Chris Nickson

FCICM FACEM BSc(Hons) BHB MBChB MClinEpid(ClinTox) DipPaeds DTM&H GCertClinSim

Chris is an Intensivist at the Alfred ICU in Melbourne and is an Adjunct Clinical Associate Professor at Monash University. He is also the Innovation Lead for the Australian Centre for Health Innovation and the Chair of the Australian and New Zealand Intensive Care Society (ANZICS) Education Committee. He has a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives. After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia's Northern Territory, Perth and Melbourne. He has since completed further training in emergency medicine, clinical toxicology, clinical epidemiology and health professional education. He coordinates the Alfred ICU's education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the 'Critically Ill Airway' course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of Lifeinthefastlane.com, the RAGE podcast, the Resuscitology course, and the SMACC conference. His one great achievement is being the father of two amazing children. On Twitter, he is @precordialthump.

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