Objective: To investigate whether a single dose of neostigmine, administered when the adductor pollicis muscle presents 2 twitches in train-of-four (TOF) stimulation, can reduce the TOF ratio in the corrugator supercilii muscle.
Patients and methods: We designed a case-control study of patients between 18 and 65 years of age classified ASA 1-2. We used 2 accelerometers--1 for the cubital nerve/thumb adductor muscle and 1 for the facial nerve/corrugator supercilii muscle. Neuromuscular blockade was induced with 0.6 mg x kg(-1) of rocuronium, and 40 microg x kg(-1) of neostigmine was administered at the third twitch in the TOF in the thumb adductor. If the TOF ratio in the corrugator supercilii fell by 10% or more at that time, the patient was classified as a case. We recorded the age, sex, weight, height, body mass index, duration of the procedure, and TOF ratio in the corrugator supercilii muscle when the neostigmine was administered.
Results: Ten cases and 10 controls were enrolled. No significant differences between cases and controls were found in any variables except the mean (SD) TOF ratio in the corrugator supercilii muscle: 70.9% (17.8%) in cases and 35.3% (7.8%) in controls (P < .001).
Conclusions: In our patients, administration of neostigmine after the appearance of the third twitch in TOF stimulation of the thumb adductor was associated with a reduction in the TOF ratio in the corrugator supercilii. The similarity between blockades of the corrugator muscle, the diaphragm, and the larynx is of clinical interest.