Question

All of the following statements about the neuromuscular blockade produced by succinylcholine are true, except:

• A. No fade on train of four stimulation
• B. Fade on tetanic stimulation
• C. No post tetanic facilitation
• D. Train of four ratio > 0.4

Hint:

Fade is the signature of a non-depolarising block, not a pure depolarising one.

Answer 1

The Correct Option is B

Step 1: Recognise the drug type. Succinylcholine is a depolarising neuromuscular blocker. In a pure phase I (depolarising) block, the response to stimulation is fundamentally different from a non-depolarising block.

Step 2: Recall the features of a phase I depolarising block. The four twitches of train of four are reduced but equally, so there is no fade. There is sustained but reduced response to tetanic stimulation, so there is no tetanic fade. There is no post tetanic facilitation. The train of four ratio stays high, typically near or above 0.7, well above 0.4.

Step 3: Test each option. Option A (no fade on train of four) is true. Option C (no post tetanic facilitation) is true. Option D (train of four ratio above 0.4) is true. Option B says there is fade on tetanic stimulation, which is a feature of a non-depolarising or phase II block, not of a pure depolarising block.

Step 4: The question asks for the exception, so we pick the false statement.

The answer is B. Fade on tetanic stimulation.