Challenge to the Pain

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.