Visually Evoked Response I N Anesthetized Man with and without Induced Muscle

The use of highly sensitive techniques for recording sensory evoked responses from the human scalp increases the likelihood that the potentials obtained contain electrical components not only from the underlying brain but also from skeletal muscle and other extraneuronal sources. Our concern over the observation of Bickford that the auditory evoked response in man has important skeletal muscle components, prompted us to study the effects of complete skeletal muscle paralysis on the visually evoked response ( VER ) in lightly anesthetized surgical patients. The effects of thiopental on the VER in man have been reported by Cig6nek ( 1961a,b ). Brazier ( 1960a,b ) also recorded the averaged visually evoked response in man and animals; she reported the modifications of the visually evoked response in animals by general anesthetics. A study of the effects of a variety of general anesthetics on the VER in man has been recently completed and is being reported elsewhere (Domino et al., 1963). Inasmuch as light general anesthesia (Stage 111, upper plane 1 after Guedel) does not markedly alter the VER in man, and in fact may enhance certain components, it was felt that surgical patients under general anesthesia could be used a.s subjects to determine the effect of skeletal muscle paralysis on the visually evoked response. Such an approach appeared justified and feasible by selecting patients in whom skeletal muscle paralysis had to be induced for tracheal intubation prior to surgery.