AS8.1-2 | Pain Physiology and Clinical Pain Assessment — Summary & Reflection

KEY TAKEAWAYS

Pain perception is a multistep process beginning at nociceptors — specialised free nerve endings that transduce noxious stimuli via Aδ (sharp, fast, first pain) and C (burning, slow, second pain) fibres. Inflammatory mediators produce peripheral sensitisation by lowering nociceptor thresholds, generating primary hyperalgesia and allodynia at injury sites. In the dorsal horn, repeated C-fibre firing triggers wind-up through NMDA receptor activation after Mg²⁺ block relief, producing central sensitisation — the neurophysiological basis of secondary hyperalgesia and many chronic pain states. The spinothalamic tract carries signals to the thalamus and then to the somatosensory cortex (sensory-discriminative dimension) and to the anterior cingulate and insular cortex (affective-motivational dimension). Nociceptive pain results from activation of intact nociceptors; neuropathic pain from injury to the somatosensory system itself and has distinct features: burning/electric-shock character, allodynia, spontaneous pain, and poor response to NSAIDs. Clinical assessment requires a systematic SOCRATES history, selection of the appropriate validated rating tool (NRS/VAS for adults; FPS-R for children; FLACC/CPOT/PAINAD for non-communicating patients), characterisation of pain type, and regular reassessment after treatment. Pain assessment is not complete until it generates a mechanistic diagnosis that directly informs a multimodal analgesic plan.

REFLECT

Think about a patient you have encountered — in a ward, outpatient clinic, or emergency department — who appeared to be in pain but was not asked about it systematically. Reflecting on the SOCRATES framework and the validated tools covered in this module, what questions were missed? How might a more structured assessment have changed the analgesic plan? Consider also: what barriers exist in your clinical environment to routine use of validated pain scales, and what systemic changes might improve pain assessment practice across the team? As a future doctor with anaesthesiology training, how would you advocate for better pain assessment standards in your hospital?