0 Thiopentone

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Thiopentone = Sodium Thiopental
Thiopental, a barbiturate, is used for the induction of anesthesia

First used in 1934 by Lundy' and Waters

Yellow amorphous powder.

pH 10.5 - 11 , therefore not to be given with Normal Saline & RL

Dose - 3-5mg/kg ;  Route: IV
Adequate induction dose will cause loss of eyelash reflex.

Used in concentration of 2.5%
Given Commonly at outer aspect of forearm (Never in anticubital fossa)

If Concentration >2.5%
  • Pain on injection
  • Venous thrombosis

Mechanism of action :
  • depress RAS
  • binds at a distinct binding site associated with a Cl- ionopore at the GABAA  receptor, increasing the duration of time for which the Cl- ionopore is open. The post-synaptic inhibitory effect of GABA in the thalamus is, therefore, prolonged.
Duration of action 
  • Determined by redistribution (not by elemination)
  • Patient looses consciousness in 30 sec and regains in 20 min.
  • With repeated doses - duration depends on elimination (Metabolized in Liver)

Systemic effects:
  • Decrease BP (Compensatory increase in Heart Rate)
  • Decreased response to hypoxia & hypercarbia.
  • Apnea (Treat with Positive pressure resp. -  IPPV)
  • Decrease Tidal Volume and Respiratory Rate 
  • Can cause bronchospasm & laryngospasm
  • Decreases Cerebral blood flow
  • Decreases Cerebral O2 consumption ( Therefore Cerebroprotective ; DOC - in Head Injury )
  • Lowers threshold for pain ( it is AntiAnalgesic)
  • Does not cause Muscle relaxation
  • Powerful anticonvulsant (refractory seizures can respond to it)
  • Decreases Renal blood flow and GFR
  • Crosses Placenta and has some antithyroid activity.
It is Microsomal enzyme inducer.
Induction of hepatic enzymes increase the rate of metabolism.

Contraindications:
Acute Intermittent Porphyria and Variegate Porphyria

Can be used in Porphyria Cutaneous Tarda



In case of inadvertent intra-arterial injection (eg: if in anticubital fossa)
  • pain , 
  • blanching hand , 
  • absent radial pulse , 
  • Secondary thrombosis
Treatment 
  • Stop injection & Leave the needle in situ (most important)
  • Flush with saline
  • Give Vasodialator
  • Brachial or stellate ganglion block
  • Anticoagulant


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