An i.v. bolus dose of thiopentone leads to loss of consciousness within 10-15 sec. The patient regains consciousness in just a few minutes. This is because it is:
## Core Concept
Thiopentone, also known as thiopental, is a barbiturate used for inducing general anesthesia. Its rapid onset and short duration of action make it ideal for procedures requiring quick recovery. The mechanism behind its effects is related to its interaction with the GABA (gamma-aminobutyric acid) receptor.
## Why the Correct Answer is Right
Thiopentone acts by enhancing the effect of the inhibitory neurotransmitter GABA at the GABA_A receptor, leading to an increase in chloride influx into neurons, hyperpolarization, and consequently, a decrease in neuronal excitability. This results in sedation, hypnosis, and ultimately, loss of consciousness. The rapid onset of action is due to its high lipid solubility, allowing it to quickly cross the blood-brain barrier. The short duration of action of thiopentone is primarily because it is rapidly redistributed from the bloodstream to tissues, particularly muscle and fat, reducing its plasma concentration and hence its effects on the brain.
## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because redistribution, not metabolism, is the primary reason for the short duration of action of thiopentone. Although metabolism does play a role in the eventual breakdown of thiopentone, it is the redistribution that accounts for the rapid recovery.
- **Option B:** This option is incorrect as it does not accurately describe the primary reason for thiopentone's short duration of action.
- **Option C:** This option might seem plausible because thiopentone does get metabolized, but it's not the reason for the quick regain of consciousness. Metabolism occurs later and doesn't explain the rapid recovery seen within minutes.
## Clinical Pearl / High-Yield Fact
A key point to remember is that thiopentone's effects are quickly terminated by redistribution, not metabolism. This characteristic makes thiopentone useful for procedures where rapid recovery is desired. A classic clinical correlation is that patients can quickly regain consciousness and resume normal activities shortly after the procedure, making it a favorable agent for outpatient surgeries.
## Correct Answer Line
**Correct Answer: D. Redistribution.**