Sodium Nitroprusside

CLASS

  • an inorganic complex

MECHANISM OF ACTION

  • vasodiator and 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

CCC 700 6

Critical Care

Compendium

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health and Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with 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 completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. 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 litfl.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.

| INTENSIVE | RAGE | Resuscitology | SMACC

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