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 –
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.
Pseudocholinesterase deficiency increasing action of syccinylcholine
Phase 2 blockade produced by succinylcholine
Undiagnosed muscular dystrophy and muscular weakness
Muscular weakness due to fasciculation produced by succinylcholine