After suxamethonium 50 mg, apnea persists for one hour –
Sch can cause prolonged apnea in patients with low plasma cholinesterase (pseudocholinesterase) or atypical (non­functional) pseudocholinesterase. The best management is to provide mechanical ventilation, maintain anaesthesia, continue monitoring and wait for spontaneous recovery. 
If spontaneous recovery does not occur fresh frozen plasma or blood can be given which provide pseudocholinesterase. Purified preparation of pseudocholinesterase is also available. However because of the risk of associated with there infusion, blood, FFP or purified pseudocholinesterase is not recommended by some authorities.
Treatment with cholnesterase is indicated
Probably an atypical cholinesterase is present
Treatment with stored blood is indicated
Apnea may be due to low serum potassium concentration