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What is Which of the following barbiturate is used for induction? and explain in detail?
Ans: a (Thiopentone) Ref: KDT, 6th ed,p. 374* Thiopentone sodium is an ultrashortacting thiobarbiturate highly soluble in water, yielding a very alkaline solution (pH 10.4)* On IV injection it produces loss of consciousness in one arm- brain circulation time * Ultrashort duration of thiopentone is because of methyl group added to it. At induction it causes mild hypokalaemia* Elimination half life of thiopentone is 10.4 hours but consciousness is regained after 15-20 min because of redistribution (drug redistributed from brain to tissues with less vascularity like muscle or fat)* 80-90% is bound to plasma proteins (mainly albumin)* Metabolized in liver and metabolic products are eliminated through kidney* MOA - inhibits function of synapse. Transmission of excitatory neurotransmitters like Ach is inhibited and that of inhibitory neurotransmitters like GABA is enhanced* Cerebral protection - cerebral oxygen consumption, cerebral metabolic rate and intra cranial tension are decreased (therefore agent of choice)* Causes hypotension and decreases intra ocular pressure* Pregnancy - crosses placental barrier and achieves high concentration in brain of fetus* Stimulates ADH action and has got antithyroid activity* * poor analgesic and muscle relaxant action* Intra arterial injection - very dreadful complication which may lead to gangrene and loss of limb if not diagnosed early* Absolute contraindication - acute intermittent porphyria and variegate porphyriaThiopentone induces enzyme aminolevulenic acid synthetase which stimulates formation of porphyrin in susceptible individuals Barbiturates Long acting- PhenobarbitoneShort acting- Butobarbitone- PentobarbitoneUltra short acting- Thiopentone- Methohexitone