Spinal cord potential evoked by trigeminal nerve stimulations

s180

LATECEREBRAL~~COMPONE~UNDWGENERALAN~ESIA E. Kcchs”,

R.-D. Treede2, J. Schulte am Esch’ and 8. Bromm2

Department of ‘Anesthesiology

and Institute of ‘Physiology,

University

D-2000 Hamburg, FRG

Hospital Eppendorf,

.

m of rnvem

Late components

of evoked cerebral potentials (EPs) reflect the painfulness

noxious stimuli, as has been shown in awake healthy subjects. This study investigates,

of phasic

whether these EPs

may also be used to monitor analgesia in patients under general anesthesia. Methods:

In 10 female

intracutaneous earlobes, over

0.590

40 stimuli.

stimuli

patients

(40-55

of 2- to 3-fold

Double

recordings

with etomidate

were

performed

and vecuronium,

thane in GZ as well as under 0.8% habthane

were

abdominal studied.

the

evening

before

10 min afterwards

surgery,

EPs due to

EEG (vertex

vs. linked

(100/s) EPs were averaged surgery,

Immediately

before

under 67% NzO and 0.8% halo-

alone in 02 (with the same and with tenfold stimulus strength).

The late EP components without anesthesia In thls patient group were comparable to those recorded

in the laboratory Pain 25: 245257, Lowering

for elective

pain threshold

Hz) and EOG were stored on analog tape. After digitization

induction of anesthesia

Besutll;

y). scheduled

individual

consisting

of a vertex negativity

at 150 ms and a positlvity

at 250 ms (cf. Bromm et al.,

1986). General anesthesia with halothane and NzO abolished these late EP components.

anesthetic

depth (NzO eliminated) dld not brlng back the EPs. But a tenfold increase in stimulus

intensity at this stage lead to reproducible

EPs in the latency range 100-400 ms, the shape of which varied

between patients. These EPs could again be suppressed by injectlon of 0.25 mg fentanyl. (;onclusions:

The present

findings

indicate

the possibility

to measure

pain related

evoked

cerebral

potentials in patients under general anesthesia. Supported by the Deutsche Forschungsgemeinschaft.

SPINAL CORD POTENTIAL EVOKED BY TRIGEMINAL NERVE STIMDLATIONS. T. Hokari*, H. Fujioka*, T. Takada* and K. Shimoji, Department of Anesthesiology,Niigata UniGrsity School of Medicine, Niigata 951, Japan Aim of Investigation: The spinal nucleus of the trigeminal nerve (TN) extends the full length of the medulla oblongata and upper segments of the spinal cord (up to C ). This study examines feasibility to record the potentials of the sp1nal nucleus of the TN from the upper cervical epidural space (ES) in man. Methods: Procedures to introduce the electrode into the posterior ES were based on the technique of continuous epidural block. The patients with facial pain were placed in a lateral position and were well flexed in order to open the inter-spaces of the vertebral column. After making a skin wheal and injecting local anesthetics over the selected inter-space aseptically, a 16-gauge Tuohy needle was inserted into the ES by paramedian approach for introducing the epidural catheter electrodes. Results: Stimulation of the supraorbital nerve did not evoke any potential change in the upper cervical ES. On the other hand, infraorbital nerve stimulation produced the initial spike and a subsequent slow negativepositive complex. The two evoked potentials elicited by infraorbital and mental nerve stimulations constituted a mirror image of each other. The waveform characteristicsof the negative and positive complexes evoked by infraorbital nerve stimulation were very similar to those of the Nl and P2 waves in the segmental spinal cord potential, respectively. Conculsions: Therefore, the negative and positive complexes evoked by infraorbitalnerve stimulation might reflect the synchronized activity of the neurons in the spinal nucleus of trigeminus and the PAD of trigeminal nerve terminals, respectively. We have no idea why the potential evoked by mental nerve stimulation shows a reversed polarity.