Power spectral analysis of the electroencephalogram during induced total spinal block.
OBJECTIVE
To evaluate the effects of total spinal block (TSB) on brain function, TSB-induced changes in cortical electrical activities were analyzed using power spectral analysis of an electroencephalogram (EEG).


METHODS
Six patients suffering from chronic pain who were undergoing TSB therapy were studied. TSB was established with intrathecal 1% lidocaine (0.3 ml.kg(-1)) injected through the C1-2 lateral intervertebral space. Mechanical ventilation was continued via a laryngeal mask until the recovery of respiration. The EEG recording was started before TSB induction and continued until 10 min after extubation. The following processed EEG parameters were monitored: spectral edge frequency-90% (SEF90), spectral median frequency (SMF), and relative power in the frequency bands of delta, theta, alpha, beta, and the delta ratio [(alpha + beta)/delta].


RESULTS
TSB induced an unconscious state more than 40 min in all patients. During TSB, 12-13 Hz in SEF90 and 6-7 Hz in SMF were observed. These values are consistent with the previously reported prearousal threshold from general anesthesia. The other EEG descriptors did not change during the TSB-induced unconscious state.


CONCLUSIONS
The dissociation of cortical electrical activities and the clinical coma-like condition may be characteristic of the TSB-induced unconscious state.
Takahashi
M
M
Department of Anesthesiology and Emergency Medicine, Tohoku University Postgraduate Medical School, 1-1 Seiryo, Aoba-ku, Sendai 980-8574, Japan.
Murakami
M
M
Nakaho
T
T
Kato
M
M
Yamamuro
M
M
Hashimoto
Y
Y