A 70 kg athlete is taken for surgery, due to unavailability of vecuronium, succinylcholine is given repeatedly (>640mg). He now is unable to take breath and his lower limbs are paralyzed. What will be cause?
**Core Concept**
Phase II block is a rare, life-threatening complication of succinylcholine administration in patients with pseudocholinesterase deficiency, where prolonged neuromuscular blockade occurs due to impaired degradation of succinylcholine. This results in prolonged paralysis and respiratory failure, especially after repeated dosing.
**Why the Correct Answer is Right**
In this scenario, the athlete received repeated doses of succinylcholine (>640 mg), exceeding safe limits. Succinylcholine is normally hydrolyzed by plasma cholinesterase (butyrylcholinesterase). In patients with **pseudocholinesterase deficiency**, this enzyme is deficient or dysfunctional, leading to delayed hydrolysis of succinylcholine. With repeated dosing, the drug accumulates and causes **prolonged neuromuscular blockade**—this is termed a **Phase II block**. Unlike Phase I (acute) block, Phase II involves cumulative paralysis due to enzyme deficiency and repeated exposure.
**Why Each Wrong Option is Incorrect**
Option B: Succinylcholine causes fasciculations initially, not paralysis—this is a transient effect, not the cause of sustained paralysis.
Option C: Hidden muscle dystrophy may present with weakness but does not typically cause immediate, severe paralysis after succinylcholine.
Option D: While pseudocholinesterase deficiency is a known cause of prolonged succinylcholine blockade, **Phase II block** is the *clinical manifestation* of this condition in repeated dosing. Thus, D is a contributing factor but not the best answer as per question intent.
**Clinical Pearl / High-Yield Fact**
In patients with pseudocholinesterase deficiency, **repeated succinylcholine doses** can lead to **Phase II block**—a severe, prolonged paralysis. Always avoid succinylcholine in patients with known enzyme deficiency or in cases of repeated dosing.
✓ Correct Answer: A. Phase II block