Kazuo Hanaoka, M.D., Ph.D
Chairman and Professor, Department of Anesthesiology
Faculty of Medicine , The University of Tokyo , Japan
Pain must be one of the most unpleasant sensation to the human
beings since the ancient period. However, pain is different from the other sensation such
as a visual and auditory sensation. Because we cannot feel and hear the same pain at the
same time and in the same grade. That is the reason why the study of
pain is so much difficult and is not scientific for a long time. I
would like to talk the mechanism of pain and the treatment of pain as a special lecture.
1) Nerve impulse is produced by adequate nociceptive stimulation on
the nociceptor. That impulse conducts through peripheral nerve to the dorsal horn of the
spinal cord. Especially A d fiber and C fiber of neural fiber are correlated with the
impulse of pain sensation from the nociceptor. After the impulse enters into the dorsal
horn of the spinal cord , neurotransmitter releases from a primary neuron to secondary
neuron. The axon of the secondary crosses the spinal cord, reaches to the opposite site
and goes up to the thalamus via spinothalamic pathway. Finally, the nociceptive impulse
enters into the sensory area oin the brain cortex. And also the descending pathway of
inhibitory system is very important. Because the autoregulatory system of pain inhibition
controls the nociceptive impulse at the dorsal horn of the spinal cord. Besides, the gate
control system is considered to regulate the nociceptive impulse at the same dorsal horn
of the spinal cord. I would like to introduce our laboratory where the spinal cord
analgesic mechanisms are investigated including morphine analgesia mechanisms. Epidural
morphin , at the present, is very useful and popular analgesic method during
intraoperative and postoperative period.
2) The treatment of pain. The postoperative pain is considered as
typical acute pain. There are many methods of treatment of postoperative pain. For the
postoperative pain relief, we have several methods. Epidural analgesia is one of the very
popular and useful methods. Recently, the concept of pre-emptive analgesia and patient
controlled analgesia is considered to be very important. Especially, pain sensation makes
a kind of memory substances which makes a long duration of pain. Therefore, the concept of
pre-emptive analgesia is very important.
Because preemptive analgesia prevents the production of memory
substances in the spinal cord and supraspinal level. Very popular method for the
preemptive analgesia is epidural analgesia which gets a analgesic effect with local
anaesthetics before the start of surgical procedures. Anyway, as a , we pain clinicians,
we would like to give the patient pain free during the perioperative period and nerve
block procedures. I introduce the lidocaine patch which is very useful and convenientto
prevent the pain sensation by the insertion of intravenous catheter, the injection of
trigger point, postherpetic neuralgia and so on.
