Thiopentone Flashcards
What is the onset and offset of action of thiopentone?
Onset time: 30 seconds Offset time: 5-10 minutes
How is thiopentone metabolised?
Metabolism: In the liver to the active oxybarbiturate derivative: pentobarbital and two other inactive metabolites.
The plasma concentration of the active metabolite is very low when thiopentone is used as an induction agent. However when it is used as an infusion then it will accumulate.
Describe the effects of thiopentone on the different systems?
CNS: Hypnotic, anti-epileptic, antanalgesic
CVS: direct cardiac supression resulting in reduced CO.
RS: Dose-dependent reduction in minute ventilation, commonly with a short period of apnoea.
What are some of the potential complications of thiopentone?
Extremely painful and limb-threatening if given intra-arterially.
Urgent treatment includes: Saline dilution, papaverine 40 mg to dilate the artery and sympathetic blockade to improve blood flow.
Hypersensitivity reactions: Approximately 1 in 15000.
Absolutely contraindicated in porphyria.
What chemical class does thiopental belong to and what physicochemical properties does it have?
It is a thiobarbiturate.
It is highly lipid-soluble and a weak acid with a pKa of 7.6.
Approximately 60% of free thiopental is in the unionized form, which is more lipid-soluble.
About 75-80% is bound to plasma proteins.
What is the induction dose of thiopentone?
3-7mg/kg
How is thiopentone stored?
In a vial containing: 500 mg of the thiopental sodium salt, together with sodium carbonate and is stored under nitrogen.
When mixes with 20ml of sterile water it creates a 2.5% solution (25mg per ml) with a ph of 10.5.
This high pH is required to stop the insoluble acid from precipitating out of solution.
