Self-taming of Succinylcholine-induced Fasciculations

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Abstract
Succinylcholine [SCh] a depolarizing agent, acts on the neuromuscular junction to produce initial muscle fasciculations before the onset of block. These fasciculations are attributed to a prejunctional SCh depolarizing action which results in repetitive firing of the motor nerve terminals and antidromic discharges that manifest as uncoordinated muscle fasciculations. This is followed by failure of invasion of the motor terminals'' depolarized part by the nerve action potential, resulting in neuromuscular block. Pretreatment in humans with a subparalytic dose of nondepolarizing relaxant is recommended to prevent SCh-induced fasciculations. The competitive and antagonistic interaction can delay onset and decrease the degree of SCh-induced block. Using labeled depolarizing agents, it was shown that skeletal muscle uptake can be markedly inhibited by paralytic doses of d-tubocurarine. Adequate block in patients pretreated with nondepolarizing neuromuscular blockers may be restored by increasing the SCh dose by 50-70%. The patients'' responses to nondepolarizing relaxants show wide variation which upsets the balance of doses in occasional patients and predisposes to incomplete SCh-induced block. Self-taming of SCh-induced muscle fasciculations by pretreatment using a smaller dose (.apprx. 0.15 mg/kg) is not associated with paradoxical antagonism and might be more adequate than nondepolarizer pretreatment which antagonize the fasciculations and the SCh block. The pretreatment CSh dose does not produce significant fasciculation, probably because of its small amount. Its taming effect may be attributed to induction of neuromuscular desensitization and/or accommodation. The depolarization achieved by the subsequent full SCh dose may be enough to produce neuromuscular block without reaching the threshold necessary for electrical excitation of the nerve terminals and muscle membrane. Self-taming is a simple technique that can be applied clinically to minimize the initial SCh-induced muscle fasciculations while providing optimal neuromuscular block.

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