Thiopentone

INTRODUCTION:
  • Thiopentone is a short acting barbiturate used in the induction of anaesthesia.
  • Anaesthetic barbiturates are derivatives of Barbituric acid with an oxygen or sulfur at 2 position.
  • The three barbiturates commonly used for clinical anaesthesia are :
  1. Sodium thiopental
  2. Thiamylal
  3. Methohexital
  • Thiopentone is supplied as powder containing the sodium salts with 6% sodium carbonate.
  • The addition of sodium carbonate to the powder makes it water soluble.
PHARMAKOKINETICS:
It prevents it from precipitating
  • Thiopentone is used for the induction of anaesthesia because it has a very rapid onset of action.
  • The typical induction dose (3-5 mg/kg /2.5%) of thiopentone produces unconsciousness in 10-30 seconds with a peak effect in 1 minutes and duration of anaesthesia of 5-8 minutes.
  • Action of this drug terminates quickly because of rapid redistribution.
  • Thiopentone is highly lipid soluble, therefore its redistribution is very rapid and this accounts for its short duration of action.
  • Sulphur is added to increase the lipid solubility of thiopentone.
  • Thiopentone is given intravenously.
  • It produces little to no pain on injection.
  • Venoirritation can be reduced by injection into larger non hand veins and by prior intravenous injection of lidocaine.
  • If sometimes thiopentone inadvertently enter intraarterial circulation it causes severe inflammatory and potentially necrotic reaction.
ACTION:
  • C.N.S.
  1. Besides producing a general anaesthesia, barbiturates reduce the cerebral metabolic rate, as measured by cerebral oxygen consumption (CMRO2) in a dose dependent manner.
  2. As a consequence of the decrease in (CMRO2) cerebral blood flow and intracranial pressure are similarly reduced.
  3. Because it markedly lowers cerebral metabolism, thiopentone has been used as a protectant against cerebral ischemia.
  4. Thiopentone also reduces intraocular pressure.
  5. Presumbaly in part due to their CNS depressant activity barbiturates are effective anticonvulsants.
  6. Thiopentone in particular is a proven medication in the t/t of status epilepticus.
  • Respiratory
  1. Theiopentone is respiratory depressants.
  2. It causes dose dependent decrease in minute ventilation and tidal volume with a smaller and inconsistent decrease in respiratory rate.
  • Thiopentone in cardiovascular system
  1. Thiopentone produces dose dependent decrease in blood pressure.
  2. The effect is primarily due to vasodilation, particularly venodilation and to a lesser degree to direct decrease in cardiac contractility.
  3. Hypotension can be severe in patients with impaired ability to compensate for vendilation such as those with hypovolemia, cardiomyopathy, valvular heart disease, coronary artery disease, cardiac tamponade and b adrenergic block.
USES:
  • Narcoanalysis
  • Reduction of ICP
  • Head Injury
  • Duchenne muscular dystrophy for tendon lengthening procedure
  • RTA
  • Seizure
ADVERSE EFFECT:
  • Thiopentone has no clinically significant effect on hepatic, renal or endocrine systems.
  • Thiopentone on extravasation or intraarterial injection cause intense pain and even necrosis.
  • Thiopentone (Barbiturates) can induce fatal attacks of porphyria in patients with acute intennittent porphyria and are contraindicated in such patients.
  • Intravenous thiopentone produces Rash, Pain, Spasm

CONTRAINDICATIONS:

  • Acute intermittent porphyria
Exam Question of:
  • Fall in intracranial tension, Decreases oxygen consumption of brain & Decreases metabolic rate of brain are seen as 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 a 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
  • Intra artireal injection of thiopentone causes Vasodialation,Necrosis of vessel wall, Hypotension
  • Anesthesia 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 anesthetic agent lacking analge­sic effect
  • Action of i. v. thiopentone is terminated by Redistribution

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