2021A Question 9

Explain the onset and offset of neuromuscular block at the diaphragm, larynx and adductor pollicis after an intubating dose of vecuronium. What are the clinical implications of these differences?

Examiner Report

29.5% of candidates achieved a pass in this question.

The major domains assessed in this question were:

• The definition of an intubating dose of vecuronium
• How the specified muscles differ in terms of fibre types and the sensitivity of these types to non-depolarizing muscle relaxants
• The relative onset and offset of blockade at the different muscle groups and the factors that accounted for these differences
• The clinical implications of these differences for intubating and extubating

Accurate graphs demonstrating the relative speed of onset and offset of block at peripheral vs central muscles, supplemented with an explanation were given credit.

Common problems included:

• Ranking muscle groups by speed of onset or offset without further explanation
• Listing factors affecting speed of onset or offset without explanation
• Addressing only the onset of blockade; both onset and offset needed to be addressed to pass
• Only addressing the clinical implications of differences in onset (timing of intubation) or offset (timing of extubation) but not both

Detailed explanation of the mechanism of neuromuscular blockade for all muscle groups did not explain the differences in speed of onset between different muscle groups and therefore did not attract marks.

Model Answer

Structure:

• Introduction
• Table
• Graph
• Implications

Introduction

Table

Implications