Physiology and Pathophysiology of Pain

A basic understanding of the pain pathway is important for the appropriate and effective treatment of pain. The pain pathway is composed of a series of integrated anatomical structures and physiologic processes that are dynamic and may change their structure or process according to pain source, intensity and/or duration. Pain technically doesn't occur in anesthetized patients since the cognitive or emotional response would be prevented by the anesthetic. Although the pain centres in the brain don't recognize the pain during anesthesia, it is waiting there for the brain to perceive in recovery. Pathologic changes that occur in the pain pathway include peripheral sensitization, recruitment of fibres that normally don't carry noxious stimuli (A-beta fibres), central sensitization and dysfunction of the descending inhibitory pathway. This chapter discusses specific types of pain, namely neonatal/pediatric pain, neuropathic pain, visceral pain, breakthrough pain (BTP) and stimulus-evoked/movement-evoked pain.