[Direct effect of anesthetic inducers on the electromyographic signals of the adductor pollicis].

OBJECTIVES

To analyze the effect of thiopental, propofol, etomidate and midazolam on electromyographic study of the adductor pollicis before muscle relaxation.

PATIENTS AND METHOD: Prospective study of 96 adults ASA I-II patients (gynecologic surgery) by electromyographic (Reflexograph Datex) recording of the adductor pollicis every 20 seconds with train-of-four (TOF) stimuli. After giving informed consent, the patients were randomized for type of induction agent. We studied changes in T1 (amplitude of the first response to TOF) and the TOF-ratio (T4/T1). The induction agent (thiopental 5 mg/kg), propofol 3 mg/kg, midazolam 0.2 mg/kg or etomidate 0.3 mg/kg) was given by slow 30 s injection 100 s after calibration of the Relaxograph. Changes in T1 and the TOF-ratio were recorded until 240 s.

RESULTS

The groups were statistically homogeneous. In the thiopental group, T1 readings at 20, 40, 60 and 80 s (control times) were statistically different from the readings at 180, 220 and 240 s (after administering thiopental). T1 was significantly different at 120 and 200 s in the etomidate group.

CONCLUSIONS

Thiopental and etomidate induce slight muscle relaxation at the expense of a reduction in T1 without changing the TOF-ratio, an effect that might be useful for rapid induction. Propofol and midazolam do not affect the electromyogram of the adductor pollicis. Thus, propofol is the anesthetic induction agent of choice for clinical studies on non-depolarizing muscle relaxants given that it changes neither T1 nor the TOF-ratio.