The relation of plasma cholinesterases to response to clinical doses of succinylcholine

Abstract

The plasma cholinesterase of a normal adult is capable of destroying in vitro up to 120 mg. per minute of succinylcholme chloride. This great speed of destruction cannot be obtained in vivo, yet the normal plasma cholinesterase can effectively cope with a considerable excess of succmylcboline. The rate of destruction of succinylcholine for any given concentration of succinylcholine is proportional to the concentration of plasma cholinesterase. On slow intravenous infusion of succinyldichohne, the plasma cholinesterase must be assumed always to cause an accumulation of succinylmonochohne so that the concentration of succinylmonocholine exceeds by about 40 times the concentration of succinyldicholine. It is not yet clear whether this accumulation of succinylmonocholine is prevented by factors other than plasma cholinesterase, or whether this accumulation escapes clinical detection. In order to exert its action at the neuromuscular junction, succinylcholine must enter the extravascular space where it is not exposed to plasma cholinesterase. Thus one cannot expect the esterase to be responsible for all abnormal reactions towards succinylcholine. The sera of three patients are described, in these cholinesterase activity towards succinylcholine is too low to be measured. In all three cases the esterase has some peculiarities which are not fully explained. In one of these patients injection of 5 mg. of succinylcholine chloride was found to cause profound relaxation and 15 minutes' apnoea. © 1956 Canadian Anesthesiologists.