Key Facts

Regional anaesthesia provides targeted pain relief by blocking nerve transmission in specific body regions. It is increasingly used as a sole technique or in combination with GA as part of multimodal analgesia. Ultrasound guidance has transformed the practice.

Epidemiology

The use of regional anaesthesia is increasing in the UK, with approximately 30-40% of surgical cases now incorporating some form of regional technique. The NAP3 audit found a major complication rate of approximately 1 in 25,000 for neuraxial blocks. Peripheral nerve blocks have even lower complication rates.

Aetiology

Regional anaesthesia works by depositing local anaesthetic (LA) around peripheral nerves, nerve plexuses, or in the neuraxial space. The LA blocks voltage-gated sodium channels, preventing nerve impulse propagation. The order of nerve fibre blockade follows the principle that smaller, myelinated fibres are blocked first (autonomic > sensory > motor).

Pathophysiology

Mechanism of nerve blockade:

• LA in unionised form crosses the nerve membrane
• Ionised form blocks the sodium channel from the intracellular side
• Differential blockade: sympathetic (B fibres) blocked first, then pain/temperature (Aδ, C), then proprioception (Aβ), then motor (Aα)
• Onset time depends on pKa (closer to physiological pH = faster onset)
• Duration depends on protein binding and lipid solubility
• Potency correlates with lipid solubility

Upper Limb Blocks

• Interscalene: Shoulder and proximal humerus surgery; risk of phrenic nerve palsy (~100%)
• Supraclavicular: Arm and elbow surgery; risk of pneumothorax (minimal with USS)
• Infraclavicular: Elbow, forearm, hand
• Axillary: Forearm and hand — safest brachial plexus block

Lower Limb Blocks

• Femoral nerve block: Anterior thigh, knee surgery
• Fascia iliaca block: Hip fracture analgesia — blocks femoral, obturator, lateral cutaneous nerve
• Adductor canal block: Knee arthroplasty — motor-sparing
• Sciatic/popliteal block: Below-knee surgery
• Ankle block: Foot surgery

Trunk Blocks

• TAP (transversus abdominis plane) block: Abdominal wall analgesia
• Rectus sheath block: Midline incision analgesia
• Erector spinae plane (ESP) block: Thoracic/abdominal analgesia
• Paravertebral block: Unilateral thoracic/abdominal analgesia (breast surgery, rib fractures)

Red Flags

• Metallic taste, circumoral tingling, tinnitus — early LAST (stop injection immediately)
• Seizures, arrhythmia, cardiac arrest — severe LAST (Intralipid rescue)
• Progressive neurological deficit after block — suspect nerve injury or haematoma
• Respiratory distress after interscalene block — phrenic nerve palsy or pneumothorax

Bedside

• Pre-procedure assessment: Coagulation status, consent, block suitability
• Ultrasound: Standard of care for peripheral nerve blocks — real-time visualisation
• Nerve stimulation: Adjunct to USS; motor response at <0.5mA suggests intraneural needle tip
• Post-block assessment: Sensory and motor block distribution

Bloods

• Coagulation screen: Before neuraxial or deep blocks in anticoagulated patients
• Platelet count: Ensure adequate (>75 × 10⁹/L for neuraxial; >50 for peripheral)

Imaging

• Ultrasound: Pre-procedural scanning to identify anatomy, vasculature, and nerve targets
• CXR: If pneumothorax suspected after supraclavicular block

Special Tests

• Nerve conduction studies/EMG: If post-block neurological deficit persists >72 hours
• MRI: If nerve injury or haematoma suspected

Non-pharmacological

• Consent: Explain benefits, risks (nerve injury, LAST, infection), and alternatives
• Monitoring: Standard AAGBI monitoring during block performance; resuscitation equipment available
• Positioning: Appropriate for block type; aseptic technique

Pharmacological

• Bupivacaine 0.25-0.5%: Long-acting (4-8 hours); max dose 2mg/kg (150mg)
• Levobupivacaine 0.25-0.5%: S-enantiomer — less cardiotoxic; same doses as bupivacaine
• Ropivacaine 0.5-0.75%: Less motor block, less cardiotoxic; max dose 3mg/kg
• Lidocaine 1-2%: Short-acting (1-2 hours); max dose 3mg/kg (or 7mg/kg with adrenaline)
• Adjuvants: Adrenaline 1:200,000 (prolongs block, reduces LA absorption), dexamethasone 4mg perineural (prolongs block by 6-8 hours), clonidine 1mcg/kg
• Intralipid 20% rescue: 1.5mL/kg bolus for LAST → 15mL/kg/hr infusion

Surgical/Interventional

• Catheter techniques: Continuous infusions (bupivacaine 0.1-0.125% at 5-10mL/hr) for prolonged analgesia
• Combined spinal-epidural (CSE): For lower limb/pelvic surgery with extended post-operative analgesia

Referral Criteria

• Persistent neurological deficit >72 hours post-block — neurology referral
• Suspected LAST — immediate ALS and Intralipid protocol
• Infection at catheter site — remove catheter, microbiology input

• Peripheral nerve blocks: permanent nerve injury rate approximately 1 in 5,000-10,000
• Transient neuropraxia: occurs in 2-4% of blocks — resolves within days to weeks
• LAST: Incidence approximately 1 in 1,000-10,000 peripheral blocks; mortality now rare with Intralipid rescue
• Patient satisfaction with regional anaesthesia is consistently high (>90%)
• Continuous catheter techniques reduce opioid consumption by 40-60% post-operatively

Maximum Doses of Local Anaesthetics

LAST Management Algorithm