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Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
A 70 kg old athlete was posted for surgery, Patient was administered succinylcholine due to unavailability of vecuronium. It was administered in intermittent dosing (total 640 mg). During recovery, the patient was not able to respire spontaneously & move limbs. What is the explanation –
assistant
The correct answer is  This a case of phase II block, caused by a high dose of succinylcholine.

"After administration of 7-10 mg/kg or 30-60 minutes of exposure to succinylcholine, non-deplarizing dual or phase II block occurs".
— Millers

Option a requires specific mention here because prolonged paralysis with succinylcholine administration may also occur in pseudocholinesterase deficiency. But, this is due to the phase II block.
So, Sch can cause phase II block in two conditions:-


When Sch is administered in high doses
Patients with atypical or deficient pseudocholinesterase. It these patients it occurs at usual doses as usual amount of Sch is not metabolized.