Pain Pathways and Analgesics

Abstract

Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage. Pain is both a physical phenomenon and a psychological or emotional experience. Surgical tissue damage causes measurable systemic endocrine, metabolic, and immunological changes referred to as the surgical stress response. Noxious stimulus stimulates peripheral nociceptors, which transduce the stimuli into electrochemical impulses, and then it is carried to dorsal root ganglions of the spinal cord by peripheral sensory nerves. Stimuli are transmitted to supraspinal levels via dorsal horn neurons whose axons ascend within the spinal cord to areas in the midbrain, thalamus, and frontal cortex. Autonomic and motor response, affective-motivational response, identification of the intensity-type-location of the pain sensation, associations with memory and cognitive activities, and emotional and behavioral responses are elicited when the painful stimuli are transmitted to the brain stem. Supraspinal centers control transmission of painful stimuli by producing responses that can lead to either an increase in the transmission of pain impulses or a decrease in transmission. Chronic pain caused by rapid and long-term changes occurs in parts of the central nervous system that are involved in the transmission and modulation of pain. This abnormal processing of pain within the peripheral and central nervous system may become independent of the original painful event. Neuropathic pain is initiated or caused by a primary lesion or dysfunction in the nervous system. Relieving pain and preventing acute pain from becoming chronic pain with management options that affect all levels of the pain process are the basic principles of treatment. Opioids, nonsteroidal anti-inflammatories, local anesthetics, and centrally acting nonopioids can be used for this purpose. In acute pain treatment, multimodal analgesia can address multiple mechanisms of pain with the added benefit of reducing side effects through the use of lower doses of individual modalities. Antidepressants, antiepileptics, calcium channel blockers, alpha-adrenergic blockers, and corticosteroids can be used for chronic pain treatment. Effects of preoperative analgesia on surgical stress response, postoperative complications, and rehabilitation are irrefutable. Nonpharmacologic management like behavioral interventions and physical agents are used in multimodal approaches to analgesia.