Ans. is 'd' i.e. Induction agent of choice in shock 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 :Sodium thiopentalThiamylalMethohexitalThiopentone is supplied as powder containing the sodium salts with 6% sodium carbonate.The addition of sodium carbonate to the powder makes it water soluble.It prevents it from precipitatingThiopentone is used for the induction of anaesthesia because it has a very rapid onset of action.The typical induction dose (3-5 mg/kg) 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.Effects on systemC.N.S.Besides producing a general anaesthesia, barbiturates reduce the cerebral metabolic rate, as measured by cerebral oxygen consumption (CMR02) in a dose dependent manner.As a consequence of the decrease in (CMR02) cerebral blood flow and intracranial pressure are similarly reduced.Because it markedly lowers cerebral metabolism, thiopentone has been used as a protectant against cerebral ischemia.Thiopentone also reduces intraocular pressure.Presumably in part due to their CNS depressant activity barbiturates are effective anticonvulsants.Thiopentone in particular is a proven medication in the t/t of status epilepticus.RespiratoryThiopentone is respiratory depressants.It causes dose dependent decrease in minute ventilation and tidal volume with a smaller and inconsistent decrease in respiratory rate.Thiopentone in cardiovascular system * Thiopentone produces dose dependent decrease in blood pressure.The effect is primarily due to vasodilation, particularly venodilation and to a lesser degree to direct decrease in cardiac contractility.Hypotension can be severe in patients with impaired ability to compensate for venodilation such as those with hypovolemia, cardiomyopathy, valvular heart disease, coronary artery disease, cardiac tamponade and b adrenergic block.* Intravenous anaesthesia of choice in shock is ketamineKetamine increases blood pressure, heart rate and cardiac output.These effects are mediated due to sympathomimetic activity of ketamine.Ketamine causes inhibition of both central and peripheral catecholamine reuptake.Ketamine has direct negative inotropic and vasodilatory activity but these effects usually are overwhelmed by sympathomimetic action.Adverse effectsThiopentone has no clinically significant effect on hepatic, renal or endocrine systems.Thiopentone (Barbiturates) can induce fatal attacks of porphyria in patients with acute intermittent porphyria and are contraindicated in such patients.