[Differentiation of brain stem anesthesia from high spinal anesthesia using auditory brain stem response].

A 67-year old woman having intractable chronic postherpetic neuralgia at the neck to forearm for two years was treated with subarachnoid block. Initially, bolus of 1% lidocaine 8 ml, with methylprednisolone acetate 20 mg was injected intrathecally at 6th cervical intervertebral space. The auditory brain stem response (ABR) during high spinal block with intact consciousness was not depressed in its wave height. ABR recorded showed prolongation of latency of 3 and 5 waves and prolongation of 1-3 phase to phase interval without prolongation of 3-5 phase to phase interval. Intrathecal nerve block was then performed with 1% lidocaine 15 ml and methylprednisolone acetate 20 mg, because she complained awareness and shocking sensation with controlled respiration during the first block. She assured that she felt nothing during the second block. The ABR recorded during the second block showed near complete suppression in its height of all waves and prolongation of all wave latencies. During recovery period, 1-3 and 3-5 phase to phase interval prolongation was recorded. One can differentiate brain stem anesthesia from other state that induces unconsciousness after block which is capable of inducing accidental brain stem anesthesia. These two blocks improved activity of daily living of the patient and severity of her pain decreased to 1/5 to 1/10.