**Question:** The dose of non-depolarising muscle relaxants in a neonate is

A. 0.1-0.2 mg/kg
B. 0.2-0.3 mg/kg
C. 0.3-0.4 mg/kg
D. 0.4-0.5 mg/kg

**Correct Answer:** B. 0.2-0.3 mg/kg

**Core Concept:** Non-depolarising muscle relaxants work by blocking the nicotinic acetylcholine receptors in the neuromuscular junction, reducing the transmission of the motor nerve impulse and causing muscle relaxation. The most commonly used non-depolarising muscle relaxant is succinylcholine.

**Why the Correct Answer is Right:** In neonates, the appropriate dose of succinylcholine should be within the range of 0.2-0.3 mg/kg. This range ensures that the drug reaches the neuromuscular junction effectively without causing excessive hypotension, hyperkalemia, or respiratory depression. Succinylcholine has a shorter duration of action in neonates due to shorter half-life, which is typically 1-2 minutes compared to adults' 5-10 minutes.

**Why Each Wrong Option is Incorrect:**

A. Lowering the dose to 0.1-0.2 mg/kg may lead to inadequate neuromuscular block, resulting in inadequate surgical conditions and potential complications.

C. Increasing the dose to 0.3-0.4 mg/kg may cause excessive hypotension, hyperkalemia, or respiratory depression due to the higher drug concentration and reduced clearance in neonates.

D. Higher doses may cause the same complications as option C, and the range of 0.4-0.5 mg/kg is generally not recommended for neonates.

**Clinical Pearl:** Succinylcholine usage in neonates should be cautious and only employed when absolutely necessary due to its short duration and potential complications. The optimal choice is a dose within the range of 0.2-0.3 mg/kg for effective neuromuscular blockade while minimizing risks.