Image Based Question-65538

A 70 kg aged athlete was posted for surgery. The patient was administered with the drug shown in the picture below due to unavailability of vecuronium. It was administered in intermittent dosing (total 640 mg).

During recovery, patient was not able to breathe spontaneously & move limbs. What will be the probable reason for the same?

A. Pseudocholinesterase deficiency increasing the action of succinylcholine.

B. Phase 2 blockade produced by succinylcholine.

C. Undiagnosed muscular dystrophy and muscular weakness.

D. Muscular weakness due to fasciculation produced by succinylcholine.

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Correct Answer » B Explanation

Ans: B. Phase 2 blockade produced by succinylcholine.

Succinylcholine

It is a depolarizing relaxant, acting in about 30 seconds and with a duration of effect averaging three to five minutes
Mechanism of Action

Phase I Block:

• Succinylcholine acts as a depolarizing neuromuscular blocker by binding acetylcholine receptors at the post-synaptic neuromuscular junction end plate.

• The resultant endplate depolarization initially stimulates muscle contraction; however, because succinylcholine is not degraded by acetylcholinesterase, it remains in the neuromuscular junction to cause continuous endplate depolarization and subsequent muscle relaxation. This is termed a phase I block.

Phase II Block:

• With increasing doses of succinylcholine, a phase II block may occur.

• Continuous activation of acetylcholine receptors leads to ongoing shifts of sodium into the cell and potassium out of the cell.

• Despite this, the post-junctional membrane potential eventually moves in the direction of normal even in the continued presence of succinylcholine.

• This is due to increased activity of the sodium-potassium ATPase pump, which brings potassium into the cell in exchange for sodium.

• The receptor does not respond appropriately to acetylcholine, and the neuromuscular blockade is prolonged.

• Phase II block may be seen clinically with doses of succinylcholine >4mg/kg, but some characteristics of this blockade have been reported at 0.3mg/kg.