[Neurophysiological aspects of pain and its consequences for the anesthetist]

Nociception is a protective system of the body which prevents it from injury and tissue damage. Human beings respond to noxious stimuli by moving away. They learn by pain to avoid these situations in future. Shortly after major injury, there is a limited analgesic period allowing the body to flee the area of danger, later on, emerging pain compels the body to rest and supports recuperation. While acute pain has a certain meaning, chronic pain does not. It induces a comprehensive suffering including loss of initiative, appetite and vigilance. It reduces life-quality, often accompanied by depressive moods. Acute pain causes changes in the central nervous system leading to an increased sensitivity of nociception (hyperalgesia). During healing, the central processing of noxious stimuli is normalised taking minutes to weeks. Sometimes, unknown factors initiate chronification of pain. Changes on a molecular level in peripheral tissue as well as in the central nervous system induce "cellular early genes", a synthesis of c-fos, c-jun and other proteins favouring the chronification of pain. All efforts have to be made to depress or interrupt such a development. One of the first steps to pain prophylaxis in a hospital is an optimal surgical technique: incision, extension, limited tissue damage and minimal invasive surgery should guarantee the smallest impairment of the nociceptive system possible. However, nociceptive input is intense and of long duration and leads to central sensibilisation. Postoperative pain has lost its function as surgery anticipates healing. Pain induces a reduction of ventilation, circulation, digestion and increases the risk of other disorders. There is need of aggressive pain treatment for humanitarian reasons and for reasons of late sequelae like permanent pain and increased reduction of function. This is of pivotal importance in patients with amputations or sympathetic reflex dystrophy (SRD). Antinociception is best provided by regional anaesthesia technique with a combination of local anaesthetics and opioids which results in better outcome. Hence, regional anaesthesia techniques are strongly indicated in those patients. Good antinociception may be even more important than it is assumed today. Anand demonstrated a lower morbidity and mortality in 45 newborns undergoing cardiothoracic surgery, when general anaesthesia was performed with high-dose sufentanil versus halothane supplementary doses of morphine. Anaesthesiologists have to reconsider the quality of general anaesthesia: the antinociception of their regimen.