A COMPARISON OF THE NEUROMUSCULAR BLOCKING EFFECTS OF ATRACURIUM, MIVACURIUM, AND VECURONIUM ON THE ADDUCTOR POLLICIS AND THE ORBICULARIS OCULI MUSCLE IN HUMANS

Both the orbicularis oculi (OO) and the adductor pollicis (AP) muscles have been used to indirectly quantify the extent of neuromuscular blo ck of the respiratory muscles. To clarify any differences in response of these muscles to neuromuscular blocking drugs, the effects of two d ifferent doses of atracurium, mivacurium, and vecuronium on the AP and OO were studied. A new technique was used to measure the evoked mecha nical response of the OO with accelerometry. Fifty premedicated patien ts were anesthetized with 5-8 mg/kg thiopental and 2 mu g/kg fentanyl intravenously (ni). They were randomly allocated to receive a single d ose of either 300 or 500 mu g/kg atracurium, 150 or 250 mu g/kg mivacu rium, or 60 or 100 mu g/kg vecuronium IV. After orotracheal intubation , anesthesia was maintained with nitrous oxide 60% in Oxygen, isoflura ne 0.5%-1.5% end-tidal, and 1-2 mu g/kg fentanyl boluses as required. The evoked response of the AP after ulnar nerve stimulation was measur ed using a force transducer, and that of the OO after facial nerve sti mulation was measured with accelerometry using a piezoelectric probe f ixed to the eyelid. The following variables were recorded for each mus cle: the maximum depression of the first twitch response to the train- of-four (EMAX), the time to achievement of EMAX (TMAX), the time to re covery of the first twitch response to 25%, 50%, 75%, and 90% of contr ol value (TH 25, TH 50, TH 75, and TH 90, respectively) and the time t o recovery of the train-of-four response to a ratio of 70% (TOF 0.7). The smaller dose of each relaxant was significantly less potent than t he larger dose at the OO. TMAX was shorter for the OO than for the AP at the larger dose of each drug. TH 25 was shorter at the OO than at t he AP with 0.5 mg/kg atracurium, but there was no significant differen ce with 0.25 mg/kg atracurium. TH 25 and TH 50 were both faster at the OO than at the AP with mivacurium, but there was no difference with v ecuronium. TOF 0.7 was shorter with the smaller dose of each drug, but there was no difference with the higher doses. It is concluded that i t is possible to record the mechanical response of the OO muscle using a noninvasive method. There are differences between the responses of the OO and the AP to neuromuscular blockers that depend upon both the specific drug itself and the dose used.