Shortest acting muscle relaxant:
**Core Concept**
The question is testing the student's knowledge of the pharmacodynamics of muscle relaxants, specifically their duration of action. Muscle relaxants are a class of medications that reduce muscle tone and are commonly used in anesthesia to facilitate endotracheal intubation and in the management of muscle spasticity.
**Why the Correct Answer is Right**
The correct answer is succinylcholine, which is a depolarizing muscle relaxant that acts by mimicking the action of acetylcholine at the neuromuscular junction. Its short duration of action is due to its rapid hydrolysis by the enzyme plasma cholinesterase. Succinylcholine has a very short duration of action, typically lasting only 4-6 minutes, making it the shortest acting muscle relaxant available.
**Why Each Wrong Option is Incorrect**
**Option A:** Rocuronium - This is a non-depolarizing muscle relaxant with a duration of action that is significantly longer than succinylcholine, typically lasting 30-60 minutes.
**Option B:** Vecuronium - This is also a non-depolarizing muscle relaxant with a duration of action that is longer than succinylcholine, typically lasting 20-40 minutes.
**Option C:** Atracurium - This is a non-depolarizing muscle relaxant with a duration of action that is intermediate, typically lasting 15-30 minutes.
**Clinical Pearl / High-Yield Fact**
Succinylcholine should be used with caution in patients with underlying cardiac disease, as it can cause a transient increase in cardiac muscle contractility and potentially lead to arrhythmias.
**Correct Answer:** D. Succinylcholine.