Question

A 6 year old boy is scheduled for examination of the eye under anaesthesia. The father informs that for the past 6 months the child has been developing progressive weakness of both legs. His elder sibling had died at age 14 years. Which drug would you definitely avoid during anaesthetic management?

• A. Succinylcholine
• B. Thiopentone
• C. Nitrous Oxide
• D. Vecuronium

Hint:

Progressive limb weakness with an early sibling death suggests muscular dystrophy; never give succinylcholine here.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
This boy has progressive weakness of both legs over 6 months, and his older sibling died young at age 14. This combination should raise suspicion for an undiagnosed muscular dystrophy, even though no formal diagnosis is stated, and we must pick the drug to avoid during his anaesthetic.

Step 2: Key Formula or Approach:
In patients with muscular dystrophy or any undiagnosed myopathy, the muscle membrane carries far more acetylcholine receptors than normal, spread across the whole muscle surface rather than just at the neuromuscular junction. Succinylcholine, a depolarising muscle relaxant, opens all of these receptors at once, releasing a large amount of potassium into the blood.

Step 3: Detailed Explanation:
Succinylcholine given to a child with unsuspected muscular dystrophy can cause a sudden, severe rise in blood potassium, which can stop the heart within minutes. It can also trigger a malignant hyperthermia like reaction of high fever and muscle rigidity. Because this child's history strongly suggests a muscle disease, even without a confirmed label, succinylcholine must be avoided outright.
Thiopentone is a standard induction agent and does not carry this specific danger in muscle disease, so it remains usable.
Nitrous oxide is an inhalational agent used for general anaesthesia and has no link to the hyperkalemic risk seen with succinylcholine, so it is safe here.
Vecuronium is a non depolarising muscle relaxant. It does not cause the sudden potassium surge that succinylcholine does, though its action may be prolonged in myopathic patients, so it can still be used with care, unlike succinylcholine which must not be used at all.

Step 4: Final Answer:
Succinylcholine must be avoided in this child because of the risk of fatal hyperkalemia from suspected muscular dystrophy, so option 1 is correct.