THIOPENTONE

Thiopentone  decreases oxygen consumption, metabolic rate and ICT. That is why it is agent of choice for cerebral protection. On sleep it increases stage 2 and decreases stage 3, 4 and REM.

Thiopentone is highly lipid soluble,

therefore redistribution is rapid and this accounts for its short duration of action.

Ans. is ‘a’ i.e., Acute intermittant porphyria

o Thiopentone is contraindicated in acute intermittant porphyria.

C i.e. Rapid redistribution

C i.e. 2.5%

D i.e. All

C i.e. 5 mg/kg

C i.e. Agent of choice in shock

Thiopentone, a pale yellow powder, is ultrashort acting smooth inducing agent because of rapid redistributionQ. It is used in 2.5% conc. at 2.5 – 4.5 mg/kg mixed with 6% anhydrous Na₂CO₃ as perservativeQ

Thiopentone is contraindicated in porphyria, status asthmaticus, severe shock, pericardial temponade and uncompensated myocardial diseaseQ

A i.e. Acute intermittent porphyria

– In porphyria (AIP), barbiturates (eg thiopentone, methohexital & thiamylal), etomidate, pentazocine and ropivacaine are avoided/ contraindicatedQ whereas diclofenac, ketorolac, phenacetin, tilidine, chlordiazepoxide, nitrazepam, hydralazine, nifedipine, and phenoxybenzamine are used with extreme caution only.

Barbiturate (Thiopentone) induces aminolevulenic acid synthetase & formation of porphyrin which may precipitate actue intermittent or variegate prophyriaQ. ; so it is contraindicated in porphyria.Q

– Due to cholinergic nerve stimulation, histamine release or direct bronchial smooth muscle stimulation, barbiturates may cause bronchospasm; which would be preventable by pretreatment with atropine, so it is not C/I in asthma.

A i.e. Rash; B i.e. Pain;  C i.e. Spasm

A i.e. Vasospasm

D i.e. Pain

C i.e. Decreased (lowered) cerebral metabolism

• Barbiturates (thiopental), primarily decreases cerebral metabolism resulting in a dose related depression of cerebral metabolic oxygen consumption (CMRO2).
• Reduced CMRO2 causes progressive slowing of EEG, a reduction in rate of ATP consumption, cerebral vasoconstriction (reducing cerebral blood flow and intracranial tension) and protection from incomplete cerebral ischemia.

Thiopentone Sodium

• Thiopentone is a yellow coloured powder used as 2.5 % solution at 5 mg/kg dose for smooth induction.
• It is ultrashort acting due to rapid redistribution.
• It is contraindicated in porphyria.

A i.e. Thiopentone sodium

Barbiturates (eg thiopentone), etomidate, pentazocine are considered unsafe and should be avoided in porphyriaQ (contraindicated).

C i.e. IV lignocaine through same needle

Ans. is ‘c’ i.e., Redistribution

Three proceeses are involved in the termination of action of barbiturates: the relative importance of each varies with the compound.

Redistribution: it is important in the case of highly lipid soluble thiopentone. After iv injection the action of thiopentone is terminated in 6-10 mins by redistribution while the ultimate disposal occurs by metabolism (tl/ 2 of elimination is 9 hours).

Metabolism: drugs with intermediate lipid solubility (short acting barbiturates) are primarily metabolized in liver by oxidation, dealkylation and conjugation. Their plasma t1/2 ranges from 12 – 40 hours.

Excretion: barbiturates with low lipid solubility (long acting agents) are significantly excreted unchanged in urine. The t1/2 of phenobarbitone is 80-120 hours. Alkalinization of urine increases ionization and excretion.

Ans. is ‘c’ i.e., IV injection is painless

Ans. is ‘d’ i.e., As antidepressant

Ans. is ‘a’ i.e., Acute intermittant porphyria 

Thiopentone

• It is an ultrashort acting barbiturate.
• It has short duration of action due to rapid redistribution.
• It causes fall in BP due to vasodilatation – Cardiovascular collapse may occur if hypovolemia, shock or sepsis are present.
• It can cause respiratory depression.
• It has anticonvulsant action – agent of choice for neurosurgical procedures.
• It is the agent of choice for cerebral protection. because it decreases ICT, and cerebral metabolic rate.
• Miller 6^th/e – 330, 332 .o It is poor analgesic -f painful procedure should not be done.It produces hyperalgesia.
• It has poor muscle relaxant property.
• Extravasation of the solution or inadverent intrarterial injection produces intense pain – thrombosis and vasoconstriction can cause necrosis and gangrene.
• Treatment of this condition includes.
• Leaving needle insitu
• Brachial block
• Heparin injection to → prevent thrombosis
• Dilution of thiopentol t by injection of saline into the artery.
• Papaverine injection → to relieve spasm.
• Urokinase, streptokinase, vasodilators, steroid and lignocaine can also be used.

 Contraindications

    Acute intermittant porphyria

    Cardiovascular instability or shock.

    Respiratory obstruction  

    No availibility of airway equipments.

    Status asthmaticus