Reliability of the vestibulo-ocular reflex as an index of the effects of hypnotic drugs on the central nervous system.

The vestibulo-ocular reflex was tested after the administration of step doses of thiopentone or propanidid in 171 unpremedicated patients. The dose of thiopentone (3 mg kg-1) required to induce loss of nystagmus also abolished the response to verbal command. The dose required to inhibit the reflex in 95% of patients was 7.22 mg kg-1 and prevented adrenergic responses to nociceptive stimulation. The dose of propanidid required to induce loss of nystagmus was greater than that necessary to abolish response to verbal command. The reflex inhibition rate increased proportionally to the dose up to 8 mg kg-1; larger doses exerted a facilitatory effect and reduced the reflex inhibition rate. The vestibulo-ocular reflex is a reliable and sensitive means of demonstrating the different effects exerted by step doses of hypnotic drugs.