Multimodal Analgesia

1. Definition and Rationale

Why Multimodal?

2. Pathophysiological Basis (Targets of Multimodal Analgesia)

Noxious stimulus
      ↓
[PERIPHERAL NOCICEPTOR] ← NSAIDs, Paracetamol, Local Anaesthetics, COX-2 inhibitors
      ↓
[DORSAL HORN / SPINAL CORD] ← Opioids, Ketamine (NMDA), α2-agonists, Neuraxial techniques
      ↓
[SUPRASPINAL CENTRES] ← Opioids, GABAergic drugs (gabapentinoids), α2-agonists, Tramadol

Key Mechanisms

1. Peripheral sensitization: Tissue injury releases prostaglandins, bradykinin, substance P → lowers nociceptor threshold → NSAIDs/COX-2 inhibitors and paracetamol act here
2. Central sensitization (wind-up): Repeated C-fibre input activates NMDA receptors → sustained hyperalgesia → Ketamine (NMDA antagonist) prevents/reverses this
3. Descending modulation: Noradrenergic and serotonergic pathways modulate pain → Tramadol, SNRIs, α2-agonists (clonidine/dexmedetomidine)
4. Spinal opioid receptors: μ, κ, δ receptors → Opioids, neuraxial opioids
5. Sodium channel blockade: Conduction block in peripheral nerves → Local anaesthetics
6. Calcium channel modulation: Reduces neuronal excitability → Gabapentinoids (pregabalin, gabapentin)

3. Components of Multimodal Analgesia

A. Non-Opioid Systemic Analgesics

1. Paracetamol (Acetaminophen)

• Mechanism: Inhibits central COX-3 isoenzyme; activates descending serotonergic pathways; endocannabinoid modulation
• Dose: 500–1000 mg orally/IV every 4–6 hours (max 4 g/day in adults; 2 g/day in hepatic impairment)
• Advantages: Safe, widely available, no GI/renal side effects
• Evidence: IV paracetamol reduces postoperative opioid consumption by ~20–30% (Miller's Anesthesia, 9th ed.)
• Role: First-line, scheduled (round-the-clock), not PRN

2. NSAIDs and COX-2 Inhibitors

• Mechanism: Inhibit cyclo-oxygenase (COX-1 and COX-2) → reduce prostaglandin synthesis → reduce peripheral and central sensitization
• Examples:
  • Non-selective: Ibuprofen, diclofenac, ketorolac, indomethacin
  • Selective COX-2: Celecoxib, etoricoxib, parecoxib
• Dose examples: Ketorolac 15–30 mg IV/IM; Celecoxib 200–400 mg PO; Ibuprofen 400–600 mg PO
• Advantages: Opioid-sparing (reduce consumption by 25–35%); anti-inflammatory
• Cautions: GI ulceration, renal impairment, platelet dysfunction (non-selective), cardiovascular risk (COX-2), avoid in bone healing concerns
• Per WHO Pain Ladder: First-choice drugs, combined with paracetamol before escalating to opioids (Paediatric Urology, p. 116)

3. Tramadol

• Mechanism: Weak μ-opioid agonist + norepinephrine and serotonin reuptake inhibition
• Dose: 50–100 mg orally/IV every 6–8 hours (max 400 mg/day)
• Role: Step 2 on WHO ladder; bridge between non-opioids and strong opioids
• Cautions: Lowers seizure threshold; serotonin syndrome risk; avoid in poor CYP2D6 metabolisers

B. Opioids (Used Judiciously)

• Role in multimodal strategy: Add as Step 3 (weak opioid) or Step 4 (strong opioid) when paracetamol + NSAID insufficient (Paediatric Urology, p. 116)
• Principle: Use minimum effective dose combined with non-opioids to minimise side effects

C. Adjuvant Analgesics

4. Ketamine

• Mechanism: Non-competitive NMDA receptor antagonist → prevents central sensitization and wind-up
• Dose: Sub-anaesthetic doses — 0.1–0.5 mg/kg IV bolus; 0.1–0.2 mg/kg/hr infusion perioperatively
• Advantages: Opioid-sparing (reduces consumption 30–40% in major surgery); prevents opioid-induced hyperalgesia; bronchodilator
• Cautions: Psychomimetic effects (dysphoria, hallucinations) at higher doses; avoid in uncontrolled hypertension, raised ICP
• Evidence: Strongly supported by Cochrane reviews for reduction of postoperative opioid use and pain scores (Stoelting's Pharmacology, 5th ed.)

5. Gabapentinoids (Gabapentin / Pregabalin)

• Mechanism: Bind α2δ subunit of voltage-gated calcium channels → reduce excitatory neurotransmitter release (glutamate, substance P)
• Doses:
  • Gabapentin: 300–1200 mg PO (preoperative loading common in ERAS)
  • Pregabalin: 75–300 mg PO (faster onset, predictable pharmacokinetics)
• Advantages: Opioid-sparing; particularly effective for neuropathic component; reduces opioid-induced nausea and vomiting (by reducing opioid dose)
• Cautions: Sedation and dizziness (dose-dependent); increased respiratory depression when combined with opioids in elderly/obese
• Evidence: Pre-operative gabapentinoids reduce postoperative opioid consumption by 30–35% (Miller's Anesthesia); however, recent meta-analyses question benefit-to-harm ratio in certain populations

6. Dexamethasone

• Mechanism: Anti-inflammatory (inhibits phospholipase A2 → prostaglandins + leukotrienes); also prolongs nerve block duration when used perineural
• Dose: 4–10 mg IV single perioperative dose
• Advantages: Reduces postoperative pain, nausea, and vomiting (PONV); opioid-sparing; improves quality of recovery
• Cautions: Hyperglycaemia (monitor in diabetics); theoretically increased infection risk (single-dose unlikely to be clinically significant)

7. α2-Adrenergic Agonists

• Clonidine: 1–2 mcg/kg PO/IV; also added to neuraxial/regional techniques
• Dexmedetomidine: 0.2–0.7 mcg/kg/hr IV infusion; highly selective α2-agonist
• Mechanism: Activate α2 receptors in dorsal horn → hyperpolarization → reduced pain transmission; also reduce norepinephrine release peripherally
• Advantages: Opioid-sparing, sedation/anxiolysis, reduced PONV
• Cautions: Bradycardia, hypotension

8. Magnesium Sulphate

• Mechanism: Natural NMDA receptor antagonist (blocks Mg²⁺ channel)
• Dose: 30–50 mg/kg IV loading, then 6–25 mg/kg/hr
• Role: Intraoperative adjunct to reduce pain and opioid consumption; beneficial in spine surgery

9. Lidocaine Infusion (Systemic)

• Mechanism: Sodium channel blockade; anti-inflammatory and anti-hyperalgesic effects (beyond local anaesthetic properties)
• Dose: 1.5 mg/kg IV bolus, then 1–2 mg/kg/hr infusion
• Evidence: Particularly effective in abdominal surgery; reduces ileus, opioid consumption, and hospital length of stay (ERAS Society Guidelines)
• Cautions: Cardiac toxicity; continuous cardiac monitoring required

D. Regional and Neuraxial Techniques

10. Neuraxial Analgesia

• Epidural Advantages: Reduces pulmonary complications, accelerates bowel recovery, reduces thromboembolic risk, superior analgesia for major surgery
• Epidural Cautions: Hypotension, urinary retention, motor block, haematoma (especially with anticoagulation — follow ASRA guidelines)

11. Peripheral Nerve Blocks (PNBs)

• Single-injection or continuous catheter techniques
• Ultrasound guidance has revolutionised accuracy and safety

12. Local Wound Infiltration (LWI) and Liposomal Bupivacaine

• Surgeon-administered at wound closure
• Liposomal bupivacaine (EXPAREL®): Extended-release formulation; analgesia up to 72 hours
• Effective in knee/hip arthroplasty and herniorrhaphy

13. Intra-articular Analgesia

• Morphine, bupivacaine, ketorolac injected into joint space
• Evidence most robust for knee arthroscopy

4. Pre-emptive and Preventive Analgesia

• Pre-emptive analgesia: Administering analgesics before noxious stimulus to prevent central sensitization
• Preventive analgesia: Broader term — any analgesic intervention that prevents establishment of altered central processing, regardless of timing relative to surgery
• Clinical approach: Administer paracetamol + NSAID/COX-2 inhibitor + gabapentinoid preoperatively as part of ERAS protocols (Paediatric Urology, p. 116)
• Intraoperative regional block and/or local infiltration further consolidates this (Paediatric Urology, p. 116)

5. The WHO Pain Ladder — Adapted for Perioperative Use

STEP 4: Strong opioid (morphine, fentanyl, oxycodone)
         + Paracetamol + NSAID + adjuvants + regional technique
STEP 3: Weak opioid (tramadol, codeine)
         + Paracetamol + NSAID
STEP 2: Paracetamol + NSAID
STEP 1: Paracetamol alone
         ±Regional/local technique at all steps

6. Multimodal Analgesia in ERAS Protocols

• Pain score < 4/10 at rest
• Mobilisation within 24 hours
• Oral feeding within 24 hours
• Minimal opioid use

7. Patient-Controlled Analgesia (PCA)

• IV PCA: Most commonly morphine or fentanyl; patient self-administers bolus doses with lockout interval
• Epidural PCA (PCEA): Patient-controlled epidural — most effective for thoracoabdominal pain
• Intranasal PCA (fentanyl): Useful in paediatric and opioid-phobic patients
• Sublingual sufentanil (Zalviso®): Newer system for postoperative use

8. Special Populations

Elderly Patients

• Reduce doses of opioids, gabapentinoids, and NSAIDs
• Prefer paracetamol + regional techniques
• NSAIDs: increased renal/GI/cardiovascular risk → use COX-2 selectively and briefly
• Gabapentinoids: fall risk due to sedation/dizziness

Paediatric Patients

• Paracetamol + NSAID backbone (Paediatric Urology, p. 116)
• Regional techniques (caudal, ilioinguinal blocks) preferred over systemic opioids
• Avoid codeine in children < 12 years (FDA black box warning — CYP2D6 ultra-rapid metabolisers)

Opioid-Tolerant Patients

• Higher baseline opioid requirement
• Emphasise non-opioid modalities even more
• Consider ketamine and α2-agonists as key components
• Convert preoperative opioid to IV equivalents; do not undertreat

Chronic Kidney Disease

• Avoid NSAIDs
• Avoid morphine (M6G accumulation) → prefer fentanyl or hydromorphone
• Paracetamol safe at standard doses

Obstetric / Breastfeeding

• Paracetamol: safe
• NSAIDs: avoid in first trimester, around delivery (ductus arteriosus), limit in third trimester
• Opioids: minimal effective dose; monitor neonate

9. Outcome Benefits — Evidence Summary

10. Monitoring and Safety

• All patients on opioids require sedation scoring (Pasero Opioid-Induced Sedation Scale — POSS) and respiratory monitoring
• Gabapentinoid + opioid combination: heightened respiratory depression risk → use lower doses in elderly, obese, OSA patients
• NSAID use: Check renal function; avoid in hypovolaemia; consider PPI for GI protection
• Epidural: Hourly motor/sensory block assessment; strict asepsis; follow ASRA guidelines for anticoagulation timing
• Local anaesthetic systemic toxicity (LAST): Risk with all regional techniques → intralipid 20% must be immediately available; follow AAGBI/ASRA LAST guidelines

11. Summary: Practical Multimodal Analgesic Protocol (Adult Major Surgery)

PRE-OPERATIVE (oral, 1–2 hrs before surgery):
  • Paracetamol 1 g PO
  • Celecoxib 400 mg PO (or ibuprofen if no contraindication)
  • Pregabalin 75–150 mg PO

INTRA-OPERATIVE:
  • Neuraxial (epidural or spinal) OR peripheral nerve block
  • Dexamethasone 8 mg IV
  • Ketamine 0.1–0.3 mg/kg IV (PRN or infusion)
  • Lidocaine infusion 1.5 mg/kg/hr (abdominal surgery)
  • Local wound infiltration at closure

POST-OPERATIVE:
  • Paracetamol 1 g IV/PO q6h (scheduled)
  • NSAID (ketorolac 15–30 mg IV q6h or ibuprofen 400 mg PO q8h)
  • Epidural infusion / nerve block catheter continued 24–48 hr
  • Opioid (morphine/oxycodone) PRN for breakthrough pain only
  • PCA if no regional technique available

Key Textbook References

1. Miller's Anesthesia, 9th edition (Gropper MA, ed.) — Chapters on Acute Pain Management and ERAS
2. Stoelting's Pharmacology and Physiology in Anesthetic Practice, 5th ed. (Flood P, Rathmell JP, Shafer S) — Opioids, NMDA antagonists, adjuvants
3. Morgan & Mikhail's Clinical Anesthesiology, 6th ed. — Regional anaesthesia, postoperative pain
4. Cousins & Bridenbaugh's Neural Blockade in Clinical Anesthesia, 4th ed. — Neuraxial and peripheral nerve block techniques
5. Oxford Textbook of Palliative Medicine, 5th ed. — WHO analgesic ladder
6. Opioid Prescribing for Analgesia After Common Otolaryngology Operations (AAO-HNS Clinical Practice Guideline, p. 15) — Multimodal definition and evidence
7. Paediatric Urology (GLGCA textbook, p. 116) — Pre-emptive analgesia, WHO ladder in perioperative context
8. ERAS Society Guidelines (multiple surgical specialties, 2018–2023)

Short Note: Multimodal Analgesia

Definition

Rationale

• Pain involves peripheral sensitization, spinal wind-up, and supraspinal modulation — no single drug targets all pathways
• Produces synergistic analgesia
• Reduces total opioid consumption by 20–50%
• Fewer opioid-related side effects (nausea, respiratory depression, ileus, dependence)

Components

WHO Pain Ladder Principle

Key Benefits

• Improved pain scores and patient satisfaction
• Faster mobilisation and return of gut function
• Shorter hospital stay (ERAS protocols)
• Reduced chronic post-surgical pain risk

Special Considerations

• Elderly: Opioid-sparing strategy preferred; avoid NSAIDs if renal impairment; risk of falls with gabapentinoids (Geriatric Trauma Management, p. 46)
• Children: Avoid codeine < 12 years; prefer regional techniques
• Opioid-tolerant: Maximise non-opioid modalities; add ketamine

Summary