Karnataka PGET Anesthesia MCQ Answer 4

The correct Answer is D

Barbiturates

• Oxybarbiturate - pentobarbital and methohexital
• Thiobarbiturates - thiopental and thiamylal
  

Sodium thiopentone is used to induce general anesthesia (and also in status epilepticus). It dissolves in water and a 5% solution has a pH of 10.8. Sodium carbonate, 1.6% , is added to the powder to prevent formation of free acid on exposure to atmospheric carbon dioxide (Limited shelf life of solution.). It is therefore an extremely irritating solution.

A dose of 4-5 mg/kg intravenously produces loss of consciousness within 10 second and general anestheisa for about 5 min. The plasma half-life of the drug is 6 hours but the rapid course of action is explained by its high lipid solubility coupled with a rich penetration into the brain. The short-lived anesthesia results from the rapid fall (α phase) of the blood concentration, which occurs due to distribution of drug into the tissues. Drug is then transferred rapidly back out of the brain into the blood to maintain equilibrium. Following the initial uptake of thiopentone into the brain the main early transfer is into muscle.

Metabolism, mainly side chain oxidation, is almost complete and occurs in the liver, muscles and kidneys. The metabolites are excreted via the kidneys.

Category: Karnataka PGET 2007 MCQs