Phase II block is seen with -

Ans. is 'a' i.e., SCh infusion o Under certain conditions depolarizing agents produce dual mechanism of neuromuscular blockade which can be divided into two phases :a) Phase 1 blockRapid in onsetResult from persistant depolarization of muscle end plate.Has classical features of depolarization block.Block is not antogonized by anticholinesterases (neostigmine).b) Phase II blockSlow in onsetResults from desensitization of receptor to ACh.Resembles block produced by competitive blockers.Block is partially reversed by anticholinesterases (Neostigmine).o In man normally only phase I block is seen - typical depolarizing block.o Phase II block is seen when fluorinated anaesthetics have been given or when SCh is injected in high dose or infused continuously.o SCh also produces phase II block in patients with atypical or deficient pseudocholinesterase.