Key Facts

Acute pain management has evolved from reactive opioid-based regimens to proactive multimodal, procedure-specific protocols. The aim is to provide effective analgesia while minimising side effects and promoting functional recovery.

Epidemiology

Approximately 60-70% of surgical patients report moderate-to-severe pain in the first 24 hours post-operatively despite analgesic interventions. Inadequate acute pain management is associated with delayed recovery, prolonged hospital stay, increased morbidity, and development of chronic post-surgical pain.

Aetiology

Acute pain is primarily nociceptive, arising from tissue damage during surgery or illness. Inflammatory mediators (prostaglandins, cytokines, bradykinin) sensitise peripheral nociceptors. Central sensitisation can occur with severe or prolonged pain, contributing to hyperalgesia and potentially chronic pain.

Pathophysiology

Surgical tissue damage releases intracellular contents and inflammatory mediators, activating and sensitising peripheral nociceptors. Afferent impulses reach the spinal cord dorsal horn, where modulation occurs. Multimodal analgesia targets multiple points in this pathway: peripheral (NSAIDs, LA), spinal (epidural, intrathecal opioids), and supraspinal (systemic opioids, paracetamol). Pre-emptive analgesia (given before surgical stimulus) may reduce central sensitisation.

Mild Pain (NRS 1-3)

• Managed with regular non-opioid analgesics
• Patient mobile and functional

Moderate Pain (NRS 4-6)

• Requires weak opioid addition or regional technique
• May limit mobility and function

Severe Pain (NRS 7-10)

• Requires strong opioid ± regional technique
• Associated autonomic responses: tachycardia, hypertension
• Impairs coughing, deep breathing → atelectasis, pneumonia risk

Opioid Side Effects

• Nausea and vomiting (30-50%)
• Constipation, pruritus
• Sedation, respiratory depression
• Urinary retention

Red Flags

• Respiratory rate <8/min or sedation score ≥3 — opioid overdose (naloxone 400mcg IV)
• Escalating pain requirements — consider surgical complication
• Pain with numbness/weakness — consider nerve injury or compartment syndrome
• Persistent pain beyond expected duration — risk of chronic post-surgical pain

Bedside

• Pain assessment: NRS at rest and on movement — at least 4-hourly
• Sedation score: 0 (alert) to 3 (unrousable) — monitor with opioids
• Respiratory rate: <8/min indicates significant opioid-induced respiratory depression
• Functional assessment: Ability to cough, deep breathe, mobilise

Bloods

• Guided by clinical situation (not specific to pain assessment)

Imaging

• If escalating pain suggests surgical complication — appropriate imaging (CT, USS)

Special Tests

• Epidural assessment: Sensory level, motor block, catheter site inspection (if epidural in situ)
• Nerve block assessment: Sensory distribution, motor function

Non-pharmacological

• Education: Pre-operative explanation of expected pain and plan
• Positioning: Optimal comfort, elevation of surgical site where appropriate
• Ice therapy: For musculoskeletal pain, swelling
• Early mobilisation: Within ERAS protocols — reduces pain, complications, and length of stay
• TENS: Adjunctive for some patients

Pharmacological

Standard multimodal regimen:

• Paracetamol 1g QDS (PO or IV) — foundation
• NSAID: Ibuprofen 400mg TDS PO or diclofenac 50mg TDS PO (if no contraindication)
• Weak opioid: Codeine 30-60mg QDS or tramadol 50-100mg QDS for moderate pain
• Strong opioid: Morphine 5-10mg PO 4-hourly PRN, or PCA (morphine 1mg bolus, 5-min lockout, no background infusion)
• Adjuvants: Gabapentin 300mg pre-op (reduces post-op pain and opioid use), ketamine sub-anaesthetic 0.1-0.2mg/kg/hr IV (opioid-tolerant patients), clonidine, dexamethasone

Regional techniques:

• Wound infiltration with LA (bupivacaine 0.25%)
• Peripheral nerve blocks (single shot or catheter)
• Epidural analgesia (bupivacaine 0.1% + fentanyl 2mcg/mL)

Surgical/Interventional

• Regional techniques as above
• Wound catheter infusion (local anaesthetic into wound)

Referral Criteria

• Uncontrolled pain despite standard analgesia — acute pain team
• Opioid-tolerant patients — specialist input for analgesic planning
• Suspected chronic post-surgical pain developing — early pain team referral

• Adequate multimodal analgesia: Reduces post-operative complications by 20-30% and shortens hospital stay
• PCA: Patient satisfaction >85%; respiratory depression <1% with appropriate monitoring
• Chronic post-surgical pain: Risk reduced with aggressive acute pain management, regional anaesthesia, and gabapentinoids
• Opioid tapering: Most patients should be opioid-free within 1-2 weeks of surgery; prolonged use >3 months associated with dependence

Procedure-Specific Analgesia (Examples)

Opioid Side Effect Management