Temporal correlation of succinylcholine-induced fasciculations to loss of twitch response at different stimulating frequencies.
OBJECTIVE
The present study was undertaken to determine the time courses of succinylcholine-induced fasciculations and adductor pollicis single-twitch responses at two stimulating frequencies.


METHODS
A prospective, randomized study.


METHODS
The main operating room of a university teaching hospital.


METHODS
Forty-four patients undergoing general anesthesia and requiring tracheal intubation.


METHODS
In 22 patients, anesthesia was induced with thiopental sodium, fentanyl, and midazolam and maintained with 70% nitrous oxide in oxygen prior to the administration of succinylcholine 1 mg/kg. In another 22 patients, end-tidal isoflurane 0.75% to 1% was included in the induction regimen. Patients in each group were randomly assigned to receive ulnar nerve stimulation at either 0.1 Hz or 1.0 Hz.


RESULTS
The times at which fasciculations were first noticed and no longer visible and the times to 25%, 50%, 75%, 90%, and 100% twitch depression were recorded. These times were compared for the two rates of neurostimulation. With single-twitch nerve stimulation at 1.0 Hz, 100% twitch depression occurred 6 +/- 16 seconds following the end of fasciculations, while at a stimulating frequency of 0.1 Hz, it occurred 52 +/- 32 seconds later (p less than 0.05). At the end of fasciculations, single-twitch depression of 50% or more was noted in only 19% of patients in the 0.1 Hz groups and in all patients in the 1.0 Hz groups (p less than 0.05). In the 0.1 Hz groups, 50% twitch depression occurred 19 +/- 27 seconds after the end of fasciculations, with more than three-quarters of the patients having achieved 50% twitch depression 30 seconds following the disappearance of fasciculations. The addition of isoflurane did not significantly alter any of these times.


CONCLUSIONS
The data reveal that cessation of fasciculations may be an inaccurate clinical sign of the readiness for intubation and confirm that standardized methods of neurostimulation are necessary in the pharmacodynamic evaluation of neuromuscular blocking drugs. In settings where profound neuromuscular relaxation is not required, waiting at least 30 seconds beyond the disappearance of fasciculations should provide good intubating conditions.
Connelly
N R
NR
Department of Anesthesiology, Yale University School of Medicine, New Haven, CT 06510.
Silverman
D G
DG
Brull
S J
SJ
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004558:Electric Stimulation; D005207:Fasciculation / Q000139:chemically induced*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology*; D011446:Prospective Studies; D011897:Random Allocation; D013390:Succinylcholine / Q000494:pharmacology*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors; D014459:Ulnar Nerve / Q000502:physiology*
D013390:Succinylcholine