Key Facts

Pain is a subjective experience defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage (IASP definition). Effective pain management is a fundamental right and significantly impacts recovery, mobility, and patient satisfaction.

Epidemiology

Inadequate post-operative pain management affects approximately 30-40% of surgical patients. Chronic post-surgical pain develops in approximately 10-50% of patients depending on surgery type (highest after thoracotomy, mastectomy, amputation). Chronic pain affects approximately 28 million adults in the UK.

Aetiology

Pain classification:

• Nociceptive: Somatic (well-localised, sharp) or visceral (diffuse, cramping)
• Neuropathic: Nerve damage — burning, shooting, allodynia, hyperalgesia
• Nociplastic: Central sensitisation without clear tissue or nerve damage (e.g., fibromyalgia)
• Acute: <3 months, usually nociceptive, serves protective function
• Chronic: >3 months, complex biopsychosocial condition

Pathophysiology

Pain pathway:

1. Transduction: Noxious stimulus activates nociceptors (Aδ and C fibres)
2. Transmission: Via dorsal root ganglion to dorsal horn of spinal cord
3. Modulation: Gate control theory — inhibitory and facilitatory pathways in dorsal horn, descending modulation from brainstem
4. Perception: Cortical processing — thalamus, somatosensory cortex, limbic system

Peripheral sensitisation: Inflammatory mediators (prostaglandins, bradykinin, substance P) lower nociceptor threshold Central sensitisation: Wind-up phenomenon, NMDA receptor activation, increased excitability of spinal neurones

Acute Pain

• Proportional to tissue injury
• Associated autonomic responses: tachycardia, hypertension, sweating
• Functional impact: reduced mobility, impaired coughing, poor sleep
• Responds well to analgesics and resolves with healing

Chronic Pain

• Pain beyond expected healing time (>3 months)
• Often disproportionate to identifiable pathology
• Associated with depression, anxiety, sleep disturbance, disability
• Neuropathic features common: allodynia, hyperalgesia, dysaesthesia

Pain Assessment

• Self-report is the gold standard
• Use validated tools: NRS, VAS, verbal rating scale
• Special populations: FLACC (children <7), Wong-Baker faces, Abbey Pain Scale (dementia), BPS (ventilated ICU patients)

Red Flags

• Acute pain with neurological deficit — consider cord/nerve compression
• Escalating opioid requirements — consider surgical complication, tolerance, or dependence
• Pain out of proportion to expected — consider compartment syndrome, ischaemia, or infection
• New chronic pain after surgery with neuropathic features — consider post-surgical neuropathy

Bedside

• Pain scoring: NRS at rest and on movement — document regularly
• Functional assessment: Ability to cough, mobilise, sleep
• Opioid side effect monitoring: Sedation score, respiratory rate, nausea, constipation, pruritus

Bloods

• Not specific to pain assessment (guided by underlying cause)

Imaging

• Guided by suspected cause of pain — not routine for pain assessment per se

Special Tests

• Quantitative sensory testing: For neuropathic pain characterisation (specialist pain clinics)
• Nerve conduction studies/EMG: If neuropathy suspected
• Psychological assessment: PHQ-9, GAD-7 — chronic pain commonly comorbid with depression/anxiety

Non-pharmacological

• Education and reassurance: Explain expected pain levels and management plan
• Physiotherapy: Early mobilisation, exercises, TENS
• Psychology: CBT is the most evidence-based psychological intervention for chronic pain (NICE NG193)
• Ice/heat therapy: For musculoskeletal pain

Pharmacological

Acute pain (WHO ladder + multimodal approach):

• Step 1: Paracetamol 1g QDS + NSAID (ibuprofen 400mg TDS or diclofenac 50mg TDS)
• Step 2: Add codeine 30-60mg QDS or tramadol 50-100mg QDS
• Step 3: Strong opioid — morphine 5-10mg PO 4-hourly or PCA (1mg bolus, 5-min lockout)
• Regional techniques: Local anaesthetic wound infiltration, nerve blocks, epidural analgesia

Neuropathic pain (NICE CG173):

• First-line: Amitriptyline 10-75mg ON, or duloxetine 60-120mg OD, or gabapentin 300-1200mg TDS, or pregabalin 75-300mg BD
• Second-line: Combination of above, or tramadol short-term
• Topical: Capsaicin 0.075% cream or lidocaine 5% patch (for localised neuropathic pain)

Surgical/Interventional

• Nerve blocks: Diagnostic and therapeutic
• Epidural/intrathecal drug delivery: For cancer pain and refractory chronic pain
• Spinal cord stimulation: For CRPS, failed back surgery syndrome (NICE TA159)
• Radiofrequency denervation: For facet joint pain

Referral Criteria

• Acute pain not responding to standard multimodal analgesia — acute pain team
• Chronic pain >3 months affecting function — chronic pain service referral
• Neuropathic pain not responding to first-line agents — pain specialist
• Cancer pain — palliative care and pain team input

• Acute post-operative pain: Resolves within days to weeks with appropriate multimodal analgesia in the majority
• Chronic post-surgical pain: Develops in 10-50% depending on surgery type; risk factors include pre-existing pain, catastrophising, younger age
• Neuropathic pain: 50% achieve ≥50% pain reduction with first-line agents; often requires combination therapy
• Chronic pain: Complete resolution is uncommon; management focuses on function, quality of life, and self-management
• Opioid dependence: Risk with prolonged post-operative opioid use >5-7 days — prescribe with clear tapering plan

WHO Analgesic Ladder

Equianalgesic Opioid Doses (Approximate)

NICE CG173 — Neuropathic Pain Pharmacological Ladder