Local and regional anaesthesia

Pharmacology

• Amides – Bupivacaine, lidocaine, priocaine, ropivacaine
  • Hepatic microsomal enzymes
• Esters – Procaine, tetracaine (amethocaine)
  • Hydrolysed by plasma cholinesterase enzymes
• All reversibly block sodium channels and inhibiting propagation of nerve impulses
• Small fibres first (pain and temperature), then touch, deep pressure, proprioception and finally motor function
• Onset of action
  • Dependent on pKa (pH at which 50% of drug is ionised and 50% non-ionised)
  • If ambient pH is higher than pKa, a greater proportion of drug will be in non-ionised form, which diffuses more rapidly across lipid membranes, hence faster onset of action
    • Hence if mixed with bicarbonate get faster onset and less painful injection
  • Therefore, drugs with lower pKa have more rapid onset of action
• Duration of action
  • Dependent upon receptor affinity
  • The higher the affinity, the longer the action
  • Greater risk of systemic toxicity with longer acting agents however
  • Levopuivacaine and ropivacaine appear to have lower risk of systemic toxicity than bupivacaine

Systemic toxicity

• Occurs wth dose-related clinical progression of sodium blockade in non-target tissues (brain and heart)
• Can reduce risk by adherence to dose limitations and techniques to minimise systemic absorption
• Seizures
  • Benzodiazepines
• Cardiac arrest
  • Avoid vasopressin, beta-blockers and CCB’s for arrhythmias
  • IV 20% lipid emulsion is an effective therapy (especially if bupivacaine as very high lipid solubility)
    • 1.5mL/kg infused over 1 minutes with continuous infusion or repeat dosing according to clinical condition
    • Maximum 10mL/kg over 30 minutes
• Prilocaine and benzocaine can cause oxidation of ferric form of Hb to ferrous form, creating methaeoglobin (cyanosis once methaemoglobin concentration >1.5g/dL)

General principles of use

• Addition of adrenaline
  • Reduces systemic absorption
  • Prolongs duration
  • Helps to control wound bleeding
  • Safe for use in end-arterial fields in selected healthy patients but should be avoided in suspected digital vascular injury/PVD/Reynaud’s
• Adverse reactions
  • Most often local reactions to preservatives or adrenaline
  • True allergic reactions are extremely rare
  • Alternatives include diphenhydramine and benzyl alcohol
• Addition of sodium bicarbonate
  • Shortens onset of action by raising tissue pH and reduces pain of injection
  • 1mL of 8.4% sodium bicarbonate to 9mL of 1% lignocaine
  • 1mL of 8.4% sodium bicarbonate to 29mL of -0.25% bupivacaine
    • Can cause precipitation of anaesthetic agent (esp. bupivacaine) and accelerate the degradation of adrenaline so only add immediately before use
• Can also reduce pain of injection by:
  • 27- to 30-gauge needle
  • Slow injection
  • Warming of solution to body temperature
  • Injecting through margins of wound

Local anaesthetics

• Lignocaine
  • 3-5mg/kg (5-7mg/kg with adrenaline) up to 300mg maximum in one injection
  • Lasts 20-60 minutes (2-6 hours with adrenaline)
  • Nerve block lasts 75-120min
• Bupivacaine
  • Lasts 4-8x longer than lignocaine
  • 1.5mg/kg (3mg/kg with adrenaline)
  • Max 400mg in 24 hour period
  • Not recommended for children under 12yo
  • More cardiotoxic than lignocaine (has lower cardiovascular collapse/CNS toxicity ratio)
• Prilocaine
  • 2.5mg/kg (0.5mL/kg of 0.5%)
  • Least cardiotoxic and is absorbed into tissues prior to deflation of cuff in Bier’s block
  • Lignocaine is an acceptable alternative for Bier’s block

Topical anaesthesia

• Probably as effective as local anaesthetic infiltration for many dermal injuries
• Alkaline (pH 9) cream mixture of lignocaine and prilocaine (eutectic mixture of local anaesthetics (EMLA)) was first topical anaesthetic formulated to penetrate intact skin
• Need to apply for 60 minutes under semiocclusive dressing
• As effective as infiltration for IVC and lumbar puncture
• Liposome-encapsulated tetracaine (amethocaine – ANGEL), lidocaine and tetracaine gel are all efficacious
• Adrenaline (0.1%), Lidocaine (4%), and Tetracaine (0.5%)(amethocaine) – ALA mixture can be used on open wounds (Laceraine)
  • Onset 20-30 minutes; Duration 30-60min
  • 0.1mL/kg = 4mg/kg lignocaine

Intradermal and subdermal anaesthesia

• Intradermal injection
  • Leads to wheal
  • More painful but enhances anaesthetic effect by blocking cutaneous nerves
• Subdermal injections
  • No wheal
  • Less painful
  • Slower onset of action
• Can perform field block for contaminated wounds or directly into subdermal space for clean lacerations

Regional anaesthesia

• Always assess and document peripheral neurovascular function prior to infiltration
  • For digital nerve blocks, assess 2-point discrimination on volar pads prior (normally <6mm at fingertips and often <2mm. Compare with contralateral uninjured digit
• Topical anaesthetic prior to nerve block reduces pain of procedure
• Levobupivacaine and ropivacaine have significantly less cardiotoxicity than lignocaine or bupivacaine and longer duration of action
• Lignocaine 10-20 minutes onset; Bupivacaine 15-30min
• US shortens block performance time, reduces number of needle passes and enables lower anaesthetic doses

Digital nerve block

• Less pain with lignocaine 1% + adrenaline vs. bupivacaine 0.25% but block lasts half as long
• Palm down position
• Common digital nerves
  • Derive from median and ulnar nerves (divide at 4^th digit)
  • In distal palm, common digital nerve divides into paired palmar branches that travel on both sides of the flexor tendon sheath and innervate the lateral and palmar aspect of each digit
• Dorsal digital nerves
  • Smaller, derivated from radial and ulnar nerves, and travel on the dorsal aspect of each finger to provide sensation to the back of the finger
• Traditional technique
  • 1mL at volar aspect on one side, 1mL while withdrawing, 1mL across dorsum and 1mL at volar aspect on other side
• Transthecal or flexor tendon sheath technique
  • Can be performed in addition to or as an alternative to the prior technique but may not fully anaesthetise the distal fingertip
  • Palm up position
  • At distal palmar crease, identify the flexor tendon and insert needle aiming distally at 45 degrees
  • When feel pop, within flexor tendon sheath insert 2-3mL of anaesthetic solution
    • If feel bone first, withdraw 2-3mm and inject
  • Can also perform at base of digit in metacarpal crease

Median nerve block

• Provides anaesthesia to thumb, index, long and half of ring finger distal to proximal interphalangeal joint (proximal to this is radial nerve)
• Does not cover dorsum of thumb
• Palm up position
• Runs between flexor carpi radialis and palmaris longus tendon at proximal wrist crease
• Raise a wheal in this position under skin
• Insert until pop through deep fascia and inject 3-5mL of anaesthetic
• If bone felt before pop, withdraw 2-3mm and inject
• To increase success rate, withdraw to skin and inject medially and laterally another 1-2mL of solution at same depth
• Palmar branch of median nerve runs superficial to the deep fascia and can be blocked by withdawing the needle to the subcutaneous space and injecting another 2-3mL

Radial nerve block

• Covers dorsal thumb and dorsal lateral aspect of hand up to mid-phalanx
  • Superficial branch runs over styloid process of radius
    • Provides sensation to dorsum of thumb, index finger and lateral half of middle finger
  • Other branches run over anatomic snuff box
  • Raise wheal in subcut space just proximal to the anatomical snuffbox
  • Inject 5mL over radial styloid in subcut space
  • Then direct needle across dorsum of wrist in ulnar direction to inject a further 5mL

Ulnar nerve block

• Provides anaesthesia to the entire 5^th/half of 4^th and medial aspect of hand
• Can be palpated deep to flexor carpi ulnaris with artery and vein
• Raise wheal on medial aspect of wrist 1-2cm proximal to the distal wrist crease
• Insert needle under f.c.u. 5-10mm depth, aspirate and inject 3-5mL
• To block dorsal branches, inject 2-3mL into subcut space above the tendon of extensor carpi ulnaris

Foot and ankle blocks

• 5 nerves
  • 4 branches of sciatic nerve (deep fibular, superficial fibular, tibial and sural)
  • 1 cutaneous branch of femoral nerve (saphenous nerve)
• Should block deep nerves (tibial and deep fibular) before field blocks distort anatomy

Deep fibular block

• Deep fibular/peroneal block
  • Provides anaesthesia to first web space and small area just proximal to first and 2^nd toe on plantar aspect of foot
  • Found at level of medial malleolus between extensor hallucis longus and tibialis anterior tendon
  • Raise a wheal between the two tendons then insert needle through extensor retinaculum (or to bone and withdraw 2-3mm) and inject 2-3mL
  • Can increase success by injecting medially and laterally a further 1-2mL on each side

Posterior tibial nerve block

• Provides anaesthesia to plantar aspect of foot
  • Misses just proximal to first and 2^nd toes on plantar surface and lateral aspect (sural nerve)
• Nerve lies behind medial malleolus, deep to fascia and superficial/posterior to the artery
• Palpate posterior tibial artery and insert needle just posterior to bone or deep to fascia
• Inject 2-3mL an then medially and laterally 1-2mL each side of this

Superficial fibular/peroneal nerve block

• Provides anaesthesia to dorsal lateral aspect of foot
• Traverses lateral part of ankle in subcut space between lateral malleolus and tibialis anterior tendon
• Inject 5mL interior subcutaneous space between superior aspect of lateral malleolus and tibialis anterior

Sural nerve block

• Provides anaesthesia to the lateral aspect of the ankle with extension to the plantar aspect of the foot
• Traverses posterolateral aspect of ankle in subcutaneous space between Achilles tendon and lateral malleolus
• 5-6mL of anaesthetic in band from superior aspect of lateral malleolus to the Achilles tendon

Saphenous nerve block

• Blocks the medial aspect of the ankle
• Anteromedial ankle in subcutaneous space between tibialis anterior and medial malleolus
• 5-6mL in band across this space

Facial nerve blocks

• Supraorbital and supratrochlear nerve block
  • Supraorbital nerve exits at the supraorbital foramen in line with the pupil and above the superior orbital rim
    • Supplies most of the forehead
  • Supratrocheal nerve exists from under the superior orbital rim 5-10mm medial to the supraorbital foramen
    • Supplies the bridge of the nose
  • Inject 2-3mL in subcut space just superior to the eyebrow in line with pupil, then direct needle medially and inject a further 5mL reaching to medial border of eyebrow
• Infraorbital nerve block
  • Blocks the lower lid, medial cheek, ipsilateral side of nose (not bridge) and ipsilateral upper lip
  • Exits infraorbital foramen 5-10mm inferior to midportion of the orbital rim and just superior to the maxillary canine teeth
  • Provide adequate topical anaesthesia to mucosa at gingiva
  • Dry mucosa, retract upper lip with thumb (fingers on inferior orbital rim) and insert needle at gingival reflection above canine tooth to halfway between entry site and orbital rim and inject 3-5mL of anaesthetic
  • Can feel needle tip with fingers of non-dominant hand to direct needle to site
• Mental nerve block
  • Covers labial mucosa, gingiva and lower lip adjacent to canines and incisors
  • Inferior alveolar nerve gives rise to the mental nerve that exits at the mental foramen, located inferior to the mandibular canines and first premolars
  • Topical anaesthetic to mucosa, dry and evert the lower lip
  • Insert needle at gingival reflection and direct needle inferiorly 1cm and inject 3-5mL of solution
  • Can palpate mental foramen and direct needle this way
• Auricular nerve block

• Provides anaesthesia to the entire ear
• Anteriorly: Auriculotemporal nerve
• Posteriorly: Greater auricular nerve and mastoid branch of lesser occipital nerve
• Raise a wheal in subcut space inferior to the auricle
• Direct needle into subcut space anterior and superior injecting 2-3mL while withdrawing
• Redirect posterior and superior and deposit a further 2-3mL of local anaesthetic
• Repeat from superior aspect of ear both anteriorly and posteriorly

Serratus anterior block

Useful to cover lateral rib fractures

Large volume of LA (30-40mL) means cephalocaudal spread covers multiple rib levels

Procedure

• Patient is supine, sitting up or lying on unaffected side
• Transducer placed transversely at anterior border of latissimus dorsi (triangular structure) near maximal region of pain
• Anterior or posterior in-plane method used to inject local anaesthetic between latissimus dorsi and serratus anterior (underlying)
• Hydrodissection will see the muscles separate with anterior-posterior spread of fluid

Erector spinae block

Covers posterior and far-anterior rib fractures

Large volume of LA (30-40mL) means cephalocaudal spread covers multiple rib levels

Procedure

• Patient positioned sitting up or on unaffected side
• Transducer placed on back in cephalocaudal orientation
• Curved rib identified and transducer shifted medially until image is lost then regained as a tombstone (square-top) transverse process
• Local anaesthetic then injected using in-place technique to separate erector spinae muscles from transverse process
• Can insert needle up to transverse process, then retract 1-2mm and inject

Individual intercostal nerve block

• Clinical observation suggests better pain control and improved lung function as compared to parenteral analgesia
• A good block will last 8-18 hours
• Run inferior the artery and nerve in the subcostal space
• Ribs 1-6 are difficult to block due to the scapula and rhomboids
• For both anterior and posterior rib fractures, the ideal location is at the rib angle, approximately 6cm lateral to the midline
• Blocking posterior to the midaxillary line ensures analgesia to the lateral cutaneous and anterior branches of the intercostal nerves
• Retract skin cephalad at target site, raise wheal in subcut space and insert needle bevel up with syringe lower than entry site (10-15 degrees)
• Continue to bone, release skin and walk needle caudally until drops off inferior edge of rib then advance 3mm (in subcostal groove)
• Aspirate and deposit 2-5mL of anaesthetic
• Monitor for pneumothorax for at least 30 minutes
• CXR onlyif clinical signs (coughing, SOB, hypoxia)
• Pneumothorax in 8-9% of patients, or 1.4% for each individual intercostal block

Femoral nerve block

• Can be isolated femoral nerve block OR three-in-one (femoral, obturator and lateral femoral cutaneous nerves)
  • Femoral nerve block will cover anterior thigh and medial leg (saphenous)
  • Three-in-one will cover these + obturator and lateral femoral cutaneous nerve distribution
• Proven to result in more rapid achievement of lowest pain score with less narcotic dosing
• USS allows more complete block, lower LA volume and less vascular injury
• Excellent option for elderly patients with proximal femur or hip fractures
• If obese, place pillow beneath hip and retract abdominal pannus away
• 3mg/kg bupivacaine 0.5% (5mg/mL)
  • 0.2mL/kg up to 10mL = 1mg/kg up to 50mg
• 3mg/kg of ropivacaine 0.75% (= 7.5mg/mL)
  • Typically 20mL (150mg) diluted up to 30-40mL with N/saline is an excellent choice with lower cardiac toxicity and long duration
• Distal pressure during insertion of 20-30mL of anaesthetic can allow cephalad migration of agent to cover three-in-one

Fascia iliaca compartment block

• Covers femoral nerve and lateral femoral cutaneous nerve
• Injection of 40mL 0.25% bupivacaine (or ropivacaine 0.75%) 2.5cm distal to point 1/3 of the way from ASIS to pubic tubercle and lateral to the femoral artery pulse
• Two-pops must be felt (fascia lata and fascia iliacus)
• Ultrasound-guided
  • Hold transducer transversely close to the femoral artery and femoral crease
  • Anatomy
    • Fascia iliaca is anterior to the iliacus muscle
    • Both the femoral and lateral femoral cutaneous nerves lie under this

• Needle is inserted at lateral aspect of probe using an in-plane technique with tip of needle seen to go through fascia iliacus (2nd pop)
• Hydrodissection then used (with saline or LA) to see fascia iliacus separate from iliacus/iliopsoas muscle and neurovascular bundle appears to float in black fluid
• Need 30-40mL of total fluid volume to get medial-lateral spread of LA to hopefully cover femoral nerve +- LCFN
• Can place a catheter after this to provide ongoing anaesthesia

Haematoma block

• Waned in popularity mainly due to misconception of risk of infection
• Position needle in haematoma (can be difficult and USS may assist this)
• Aspirate blood
• Inject 5-15mL of agent into fracture site
• Ensure maximum dose of LA is not exceeded as could possibly by vascular site
• Do not perform in open or contaminated fractures

Bier’s block

• Provides dense anaesthesia to a limb for up to 60 min without GA/procedural sedation
• Provides no post-procedure pain control
• One small gauge IV in affected extremity (preferably distal/near to injury) and one in unaffected extremity for fluids/sedation if needed
• Padding beneath specialised double pneumatic tourniquet
• Exsanguinate affected limb by elevating for 3-4 minutes
• Inflate distal cuff first, followed by proximal cuff and ALWAYS CHECK FOR PULSE PRIOR TO IV DELIVERY OF DRUG
  • 250-300mmHg in upper limb and 350-400mmHg in lower limb (or 100mmHg above SBP in limb being anaesthetised)
• Inject Prilocaine 0.5% 3mg/kg (0.6mL/kg) for upper limb or 4mg/kg (0.8mL/kg) for lower limb blocks
  • Lignocaine is a suitable alternative
• Onset of anaesthesia is usually within 5 minutes
• Sensation of warmth/cold and skin becomes mottled
• May retain varying degrees of sensation to touch, deep pressure and motor function
• Remove IV in affected extremity once adequate anaesthesia obtained
• If pain at proximal cuff, re-inflate the distal cuff and slowly deflate proximal cuff
• Release cuff only after 30 minutes has elapsed (to allow tissue distribution of prilocaine), lower for 5-10 seconds, then reinflate for 1-2 minutes 3-5x to prevent any bolusing of LA
  • No more than 1 hour to prevent ischaemic complications
• Monitor for 30 minutes afterwards

Last Updated on August 30, 2024 by Andrew Crofton