Multimodal Analgesia

Pain has several stages, and different treatments interrupt different stages. Tissue injury activates nociceptors through inflammatory mediators; this is transduction. Signals then travel along peripheral nerves to the spinal cord and brain, which is transmission. Spinal and descending pathways can amplify or inhibit those signals, called modulation, before the brain interprets them as pain, called perception. Multimodal analgesia deliberately combines treatments with complementary targets rather than repeatedly increasing one drug. NSAIDs and COX-2 inhibitors reduce prostaglandin production and therefore decrease inflammatory sensitization at the injury site. Local anaesthetics block voltage-gated sodium channels, preventing nerve conduction; a peripheral nerve block can therefore interrupt transmission before the signal reaches the central nervous system. Opioids act mainly at mu receptors in the brain and spinal cord, changing the response to painful input and its perception. Acetaminophen has predominantly central analgesic effects, although its mechanism is not fully defined. Gabapentinoids affect calcium-channel signalling and may help when neuropathic pain is part of the picture. These effects can be additive: the patient may obtain adequate relief from several modest interventions without the sedation, constipation, nausea,...