Pain Assessment and Management
Assessment
Start with total pain: physical nociception plus psychological, social, and spiritual contributors. Use a validated scale (numeric rating, faces, or behavioral tools such as PAINAD in advanced dementia). Classify the pain - nociceptive somatic, nociceptive visceral, neuropathic, or mixed - because neuropathic pain responds poorly to opioids alone and needs an adjuvant.
Opioid fundamentals
Anchor the equianalgesic table: morphine 30 mg oral = 10 mg parenteral; oxycodone 20 mg oral; hydromorphone 7.5 mg oral = 1.5 mg parenteral. Breakthrough dosing is 10–15% of the total daily dose, offered as needed about hourly. Titrate short-acting opioid to effect, then convert to a long-acting formulation once requirements are stable. In renal failure avoid morphine (accumulating metabolites) and prefer hydromorphone or fentanyl. Avoid codeine and tramadol because of CYP2D6 variability and boxed warnings, and avoid meperidine entirely (neurotoxic metabolite).
Rotation and adverse effects
When rotating, reduce the calculated equianalgesic dose by 25–50% for incomplete cross-tolerance (more for methadone), then titrate. Constipation never tolerates - prescribe a stimulant prophylactically. Nausea and sedation usually fade within days. For respiratory depression, dilute naloxone and titrate to respiratory rate, not to full arousal, which would precipitate a pain crisis.
Adjuvants
Bone pain: NSAIDs, corticosteroids, radiation, bisphosphonates. Neuropathic pain: gabapentinoid, tricyclic, or SNRI. Visceral colic or obstruction: anticholinergics, octreotide.
Worked example: a patient takes morphine extended-release 30 mg twice daily plus four 10 mg immediate-release doses in 24 hours - 100 mg oral per day. Divide by 3 for the parenteral dose (~33 mg), reduce 25% for cross-tolerance (~25 mg/day, about 1 mg/hour), and set the breakthrough dose at ~2.5 mg parenteral.