Local anaesthetics: differential block: practice question

A Anaesthesia question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Anaesthesia · Local anaesthetics: differential block

Sample item

In spinal anaesthesia, which sequence describes the order of loss of function?

AMotor, then touch, then painBSympathetic, then pain and temperature, then touch, then motorCAll modalities are lost togetherDTouch, then pain, then sympathetic

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Sympathetic, then pain and temperature, then touch, then motor

Thin myelinated B fibres of the sympathetic system are blocked first, then A-delta and C fibres for pain and temperature, then A-beta for touch and finally large A-alpha motor fibres. The sympathetic block extends about two segments higher than the sensory block.

Option by option

A. Motor, then touch, then pain
Motor is the last to be blocked.
B. Sympathetic, then pain and temperature, then touch, then motor (correct)
Correct. Thin fibres are blocked before thick fibres.
C. All modalities are lost together
Modalities are lost in sequence.
D. Touch, then pain, then sympathetic
Sympathetic block occurs first.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Anaesthesia question

What is the answer to this Anaesthesia question?

The best answer is B, Sympathetic, then pain and temperature, then touch, then motor. Thin myelinated B fibres of the sympathetic system are blocked first, then A-delta and C fibres for pain and temperature, then A-beta for touch and finally large A-alpha motor fibres.

Why is "Motor, then touch, then pain" not the answer?

Motor is the last to be blocked.

Why is "All modalities are lost together" not the answer?

Modalities are lost in sequence.

Why is "Touch, then pain, then sympathetic" not the answer?

Sympathetic block occurs first.

What concept does this question test?

It tests Local anaesthetics: differential block in Anaesthesia. The sympathetic block extends about two segments higher than the sensory block.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Local anaesthetics: differential block?

Make a table of each agent, its key advantage and its main side effect. Then use the flashcards and the other Anaesthesia questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.