This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Muscle relaxants, Subject name: Anaesthesia
After suxamethonium 50mg, apnea persists for one hour -- 
Select and explain. 
A. treatment with cholnesterase is indicated, B. Probably an atypical cholinesterase is present, C. Treatment with stored blood is indicated, D. Apnea may be due to low serum potassium concentration
B: Probably an atypical cholinesterase is present
Answer: B: Probably an atypical cholinesterase is present 
Explanation: Suxamethonium is a depolarising muscle relaxant used to rapidly gain optimal intubating conditions. It is normally metabolised within 5 minutes by plasma cholinesterase. Some patients lack this enzyme or have an altered enzyme that does not metabolise the suxamethonium as rapidly. These patients may remain paralysed for a prolonged period after a standard dose of suxamethonium and rely on renal elimination. This condition is often referred to as suxamethonium apnea