Thiopentone
THIOPENTONE
- Ultrashort-acting thiobarbiturate.
- Used in induction of anaesthesia due to rapid onset of action.
- Very alkaline solution.
- Must be prepared freshly before injection.
- Highly soluble in water.
- Supplied as powder containing sodium salts with 6% sodium carbonate.
- Sodium carbonate is for water solubility.
PHARMACOKINETICS:
- Un-dissociated form is highly lipid soluble contributes to,
- Very rapid redistribution.
- Instant entry into the brain.
- Very short duration of action.
- Quick termination of drug action.
DOSE:
- Given intravenously.
- Typical induction dose: 3-5 mg/kg /2.5%.
- Produces unconsciousness in 10-30 seconds.
- Peak effect in 1 min.
- Duration of anaesthesia: 5-8 minutes.
ACTION:
C.N.S:
- General anaesthesia.
- Reduces cerebral metabolic rate.
- Measured by cerebral oxygen consumption (CMRO2) in dose-dependent manner.
- Decreased CMRO2 results in reduced cerebral metabolism & subsequently cerebral blood flow & intracranial pressure.
- Hence used as “Protectant” against cerebral ischemia.
- Also reduces intraocular pressure.
- Has CNS depressant activity – Effective anticonvulsants.
- Proven medication for status epilepticus.
Respiratory:
- Causes respiratory depressants in dose-dependent decrease in minute ventilation & tidal volume.
- Smaller & inconsistent decrease in respiratory rate.
CVS:
- Produces dose-dependent decrease in blood pressure.
- Due to vasodilation, reduced ventilation & direct decrease in cardiac contractility.
- Hypotension severe in patients with,
- Impaired ability to compensate for ventilation.
- Seen with hypovolemia.
- Cardiomyopathy.
- Valvular heart disease.
- CAD.
- Cardiac tamponade.
- β-adrenergic block.
USES:
- Narcoanalysis.
- Reduction of ICP.
- Head Injury.
- Duchenne muscular dystrophy for tendon lengthening procedure.
- RTA.
- Seizure.
ADVERSE EFFECT:
- On extravasation or intraarterial injection cause intense pain & even necrosis.
- Induce fatal attacks of porphyria in patients with acute intermittent porphyria.
- Intravenous injection produces rash, pain & spasm.
CONTRAINDICATIONS:
- Acute intermittent porphyria.
Exam Question
- Fall in intracranial tension, decreases oxygen consumption of brain & decreases metabolic rate of the brain are seen as an effect of thiopentone
- Dose of thiopentone is 2.5%
- Sodium carbonate is added to improve solubility of thiopentone.
- Thiopentone is Cerebro protective
- Thiopentone is contraindicated in porphyria
- Thiopentone on extravasation or intraarterial injection cause intense pain and even necrosis.
- Thiopentone is indicated in case of head injury.
- Thiopentone is indicated in increased intracranial tension.
- Thiopentone does not trigger malignant hyperthermia.
- Sodium Thiopentone is ultra short-acting due to rapid redistribution.
- Thiopentone is commonly used in narcoanalysis.
- Intravenous thiopentone produces rash, pain, spasm
- Intraarterial injection of thiopentone causes vasodilation, necrosis of vessel wall, hypotension
- Anaesthesia used in Duchenne muscular dystrophy for tendon lengthening procedure is induction with intravenous thiopentone and N20; and halothane for maintenance.
- Thiopentone is highly distributed to body fat that is an anaesthetic agent lacking analgesic effect.
- Action of i. v. thiopentone is terminated by redistribution.
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