Pathophysiology
Clinical meaning
Pain in palliative care is understood through Dame Cicely Saunders' concept of 'total pain' encompassing four dimensions: physical (nociceptive, neuropathic, visceral), psychological (anxiety, depression, fear of death, loss of control), social (family distress, financial burden, role changes, isolation), and spiritual (existential suffering, loss of meaning, guilt, anger at deity). This framework recognizes that physical interventions alone may be insufficient if psychosocial and spiritual suffering are not addressed. Cancer pain mechanisms are diverse: bone metastases activate osteoclasts and release inflammatory mediators (PGE2, NGF, bradykinin) that sensitize periosteal nociceptors; visceral pain from organ infiltration or obstruction is transmitted via poorly localized vagal and splanchnic afferents causing diffuse, deep, cramping sensations with autonomic features; neuropathic pain from tumor invasion or compression of neural structures produces burning, shooting, electric-shock sensations with allodynia and hyperalgesia. The WHO analgesic ladder (1986, updated) provides a stepwise approach: Step 1 (non-opioid analgesics), Step 2 (weak opioids), Step 3 (strong opioids), with adjuvant medications at each step. Modern practice often bypasses Step 2, moving directly from Step 1 to low-dose Step 3 opioids. Breakthrough pain (transient flare of pain...