Why Pain Assessment Is Examined
Pain is the most common presenting symptom in medicine. Assessing and managing it well is a core clinical skill examined in history-taking stations, communication stations (explaining analgesic options to a patient), and prescribing scenarios (write a post-operative analgesia prescription). The WHO analgesic ladder remains the foundation of pain management globally and is universally examined in OSCEs.
Pain History — SOCRATES
🧠 Mnemonic
SOCRATES — systematic pain history:
- S ite — where is the pain? Does it radiate?
- O nset — when did it start? Sudden or gradual?
- C haracter — what does it feel like? Aching, stabbing, burning, cramping, throbbing?
- R adiation — does it spread anywhere?
- A ssociated symptoms — nausea, vomiting, sweating, neurological symptoms?
- T iming — constant or intermittent? Episodic? Time of day?
- E xacerbating and relieving factors — what makes it better or worse?
- S everity — on a scale of 0-10; how does it affect function and sleep?
Additional pain-specific history:
- What analgesia has been tried? What effect?
- Impact on activities of daily living, work, sleep, mood
- Red flag symptoms: night pain, progressive, associated weight loss, systemic features (suggest malignancy or serious pathology)
- History of substance misuse (relevant to opioid prescribing decisions)
Pain Classification
| Type | Mechanism | Character | Example |
|---|---|---|---|
| Nociceptive — somatic | Tissue damage activating nociceptors | Well-localised, aching, sharp | MSK injury, fracture |
| Nociceptive — visceral | Hollow/solid organ distension or ischaemia | Poorly localised, colicky, cramping | Bowel obstruction, renal colic |
| Neuropathic | Abnormal somatosensory processing | Burning, shooting, tingling, electric-shock | Diabetic neuropathy, post-herpetic neuralgia, radiculopathy |
| Mixed | Both nociceptive and neuropathic components | Variable | Cancer pain, complex regional pain syndrome |
💎 Clinical Pearl
Neuropathic pain descriptors in an OSCE: burning, shooting, electric shock-like, pins and needles, skin hypersensitivity (allodynia — pain from light touch), or feeling of cold in a warm area. These features indicate adding a neuropathic agent (amitriptyline, gabapentin, duloxetine) regardless of where the pain scores on the WHO ladder.
Pain Assessment Tools
| Tool | Setting | Details |
|---|---|---|
| Numerical Rating Scale (NRS) | Standard adult | 0 = no pain, 10 = worst imaginable |
| Visual Analogue Scale (VAS) | Research, adults | 10 cm line from no pain to worst pain |
| Wong-Baker FACES | Children, cognitive impairment | 6 faces from smiling to crying |
| ABBEY Pain Scale | Non-verbal/dementia | Vocalisation, facial expression, body language, physiological changes |
| FLACC | Children under 3 | Face, Legs, Activity, Cry, Consolability |
The WHO Analgesic Ladder
Originally designed for cancer pain, now applied to all chronic and acute pain.
Step 1 — Non-opioid analgesia
- Paracetamol 1 g QDS (maximum 4 g/24 hours; reduce in hepatic impairment or low weight)
- NSAID (ibuprofen 400 mg TDS with food, naproxen 500 mg BD) — contraindicated in peptic ulcer, renal impairment, heart failure, last trimester of pregnancy
- Consider adjuvants at any step (see below)
Step 2 — Weak opioid + non-opioid
- Codeine 30-60 mg QDS (prodrug — converted to morphine by CYP2D6; poor metabolisers get no effect, ultra-rapid metabolisers get toxicity)
- Tramadol 50-100 mg QDS (also serotonin-noradrenaline reuptake inhibitor — risk of serotonin syndrome)
- Dihydrocodeine 30 mg QDS
Step 3 — Strong opioid + non-opioid
- Morphine — gold standard; 5-10 mg 4-hourly (immediate release) or MST 12-hourly (modified release)
- Oxycodone — 1.5x more potent than morphine orally
- Fentanyl patch — for stable chronic pain; transdermal; onset 12 hours
- Calculate 24-hour morphine equivalent dose before prescribing
⚠️ Red Flag
Key prescribing safety points for strong opioids:
- 1Always prescribe breakthrough analgesia (1/6 of 24-hour dose as immediate-release morphine PRN)
- 2Always co-prescribe a laxative (opioids cause constipation — universal; tolerance does not develop)
- 3Anti-emetic for first 1-2 weeks (nausea common at initiation; tolerance usually develops)
- 4Warn about drowsiness and driving (must not drive until stable on dose)
- 5Monitor for respiratory depression (RR below 10, SpO2 falling) — naloxone 400 micrograms IV is the reversal agent
Adjuvant Analgesics
| Adjuvant | Indication | Dose |
|---|---|---|
| Amitriptyline | Neuropathic pain, sleep disturbance | 10-75 mg nocte |
| Gabapentin | Neuropathic pain, post-operative, anxiety component | 300 mg nocte titrated to 300-600 mg TDS |
| Pregabalin | Neuropathic pain, generalised anxiety | 25-75 mg BD titrated to 150 mg BD |
| Duloxetine | Neuropathic pain (especially diabetic), fibromyalgia | 30-60 mg OD |
| Corticosteroids | Nerve compression (spinal metastasis, peritumour oedema), bone pain | Dexamethasone 4-8 mg OD (short course) |
| Bisphosphonates | Bone metastases | IV zoledronic acid monthly |
| Ketamine (low dose) | Opioid-refractory pain, procedure pain | IV infusion in specialist settings |
Post-Operative Analgesia — Multimodal Approach
The modern approach combines agents with different mechanisms to achieve better analgesia with fewer side-effects.
Multimodal regimen (ladder-based starting point):
- 1Regular paracetamol 1 g QDS
- 2Regular NSAID (if not contraindicated) — reduces opioid consumption by 25-30%
- 3Opioid PRN (oral immediate-release morphine 5-10 mg every 4 hours)
- 4Regional analgesia where possible (wound infiltration, peripheral nerve block, epidural)
- 5Breakthrough dose = 1/6 of 24-hour opioid dose
Frequently Asked Questions
"What is the ceiling dose of paracetamol and when should it be reduced?"
Standard adult maximum: 4 g in 24 hours (1 g every 6 hours). Reduce to 2 g/24 hours in: severe hepatic impairment, chronic alcohol excess (more than 3 units/day), severe malnutrition (BMI below 18.5), or weight under 50 kg. Paracetamol is the safest analgesic in renal impairment and in pregnancy. It should be used at every step of the WHO ladder as the baseline agent.
"How do you calculate an oral morphine equivalent dose?"
Oral morphine equivalence allows safe conversion between opioids. Common conversion factors: codeine 60 mg = morphine 6 mg (1:10 ratio); tramadol 100 mg = morphine 10 mg; oxycodone 5 mg oral = morphine 10 mg oral (1:2); fentanyl 25 micrograms/hour patch = approximately 60 mg oral morphine/24 hours. For conversion between routes: oral to IV morphine = divide by 3. Always round down and prescribe breakthrough doses.
"What is opioid-induced hyperalgesia?"
Opioid-induced hyperalgesia (OIH) is a paradoxical phenomenon where prolonged opioid use causes increased sensitivity to pain rather than analgesia. The mechanism involves NMDA receptor activation and neuroplastic changes. It is distinct from tolerance. Management: opioid rotation (switching to a different opioid), dose reduction, adding ketamine (NMDA antagonist), or addressing the underlying pain generators with non-pharmacological approaches.
"When should strong opioids be avoided or used with extreme caution?"
Caution: respiratory disease (COPD, OSA — risk of respiratory depression), head injury/raised ICP (opioids cause CO2 retention which worsens ICP), severe hepatic impairment (accumulation), renal failure (active metabolites accumulate — use fentanyl or alfentanil which have fewer renally-cleared metabolites). Relative contraindications: known substance misuse disorder (requires specialist addiction input, not an absolute contraindication for end-stage cancer or acute pain).
"What is the difference between tolerance, dependence, and addiction?"
Tolerance: the need for increasing doses to achieve the same analgesic effect — a physiological adaptation. Physical dependence: the development of withdrawal symptoms on abrupt discontinuation — also physiological, occurs with prolonged use. Addiction: a neurobiological disorder characterised by compulsive use despite harm, loss of control, and preoccupation with the drug — a psychological and behavioural phenomenon. Physical dependence is expected with long-term opioid use and does not imply addiction.
Related Posts
- Perioperative Care OSCE — post-operative pain management and prescribing
- Drug History OSCE — taking a systematic analgesia and medication history
- Palliative Care OSCE — opioid use in end-of-life and symptom management