Local Anaesthesia - Comprehensive Notes

1. MEDICINES (Local Anaesthetic Drugs)

Classification

Special Preparations

• EMLA (Eutectic Mixture of Local Anaesthetics) - lidocaine + prilocaine cream; applied to intact skin 60 minutes before venepuncture, especially in children
• Moffett's solution - cocaine + adrenaline + sodium bicarbonate; used in nasal surgery for anaesthesia and vasoconstriction
• Lidocaine 2/4/10% spray - used to anaesthetise the airway during awake fibreoptic intubation

Role of Adrenaline (Epinephrine) as Additive

• Hastens onset
• Prolongs duration of action
• Permits a higher upper dose limit (e.g., lidocaine rises from 3 mg/kg to 7 mg/kg)
• Reduces systemic absorption and peak blood levels
• Provides haemostasis in the operating field

2. TECHNIQUES

A. Topical Anaesthesia

• EMLA cream (skin for venepuncture)
• Lidocaine spray (oropharynx, larynx for awake intubation)
• Cocaine solution (nasal mucosa - provides anaesthesia + vasoconstriction)
• Benzocaine/tetracaine gels (mucous membranes)

B. Local Infiltration

• Direct injection into tissues around the operative site
• Injection made in standard fan-shaped or ring fashion
• Useful for simple lacerations, skin lesions, minor procedures
• All local anaesthetics are less effective in areas of inflammation (lower pH reduces ionisation and drug activity)

C. Peripheral Nerve Blocks

• Brachial plexus - interscalene approach: shoulder and proximal arm surgery; complications include phrenic nerve block (100%), Horner's syndrome, intravascular and spinal injection
• Supraclavicular approach: excellent for entire upper limb; risk of pneumothorax
• Infraclavicular approach: lower risk of pneumothorax; elbow and distal surgery
• Axillary approach: forearm and hand; safest approach; low complication rate
• Wrist blocks: radial, ulnar, and median nerve blocks at the wrist for hand surgery
• Digital nerve blocks: metacarpal head level injection into flexor tendon sheath or dorsal web space; excellent for fingertip injuries

• Femoral nerve block: anaesthesia and analgesia for anterior thigh, knee (quadriceps surgery)
• Sciatic nerve block: lower limb surgery; combined with femoral for complete leg anaesthesia
• iPACK block (Infiltration between Popliteal Artery and Capsule of the Knee): targets genicular nerves under ultrasound guidance; minimises motor block

• Transversus Abdominis Plane (TAP) block: local anaesthetic injected between internal oblique and transversus abdominis; blocks T6-L1 segmental nerves; effective for anterior abdominal wall analgesia after abdominal surgery
• Quadratus lumborum (QL) block: targets abdominal nerves anterior to QL muscle; wider coverage than TAP
• Erector spinae plane (ESP) block: blocks spinal nerves at various levels; used for thoracic and abdominal analgesia

D. Intravenous Regional Anaesthesia (Bier Block)

• Lidocaine injected IV into an exsanguinated, tourniquet-occluded limb
• Used for short upper limb procedures
• Bupivacaine is absolutely contraindicated for this technique

E. Central Neuraxial Blocks

• Local anaesthetic injected into the subarachnoid (intrathecal) space
• Rapid onset, dense block
• Common agents: bupivacaine (hyperbaric), lidocaine, tetracaine

• Local anaesthetic injected into the epidural space
• Slower onset, titratable, catheter allows continuous infusion
• Used in obstetrics, major abdominal/thoracic/lower limb surgery, postoperative analgesia
• Rescue lipid emulsion (20% Intralipid 1.5 mL/kg) must be available whenever epidural blocks are performed - Morgan & Mikhail's Clinical Anesthesiology, 7th ed.

• Nerve stimulator-guided blocks
• Ultrasound-guided blocks (current standard - reduces vascular puncture and local anaesthetic toxicity, allows real-time visualisation of needle tip and drug spread)

3. INDICATIONS

1. Surgical procedures on skin, subcutaneous tissue, or superficial structures
2. Minor surgical procedures: excision of skin lesions, wound repair, biopsy
3. When general anaesthesia carries higher risk: debilitating respiratory or cardiovascular disease, morbid obesity, anticipated difficult airway
4. Obstetric cases: epidural/spinal for labour analgesia, caesarean section
5. Day-case surgery: avoids prolonged recovery from general anaesthesia
6. Diagnostic and therapeutic procedures: lumbar puncture, joint injections, nerve blocks for pain management
7. Postoperative pain management: as part of multimodal analgesia, reduces opioid requirements
8. Awake procedures: fibreoptic intubation (lidocaine airway spray), awake craniotomy
9. Patients who refuse general anaesthesia
10. Regional anaesthesia as the sole technique for upper/lower limb surgery, hernia repair, perianal surgery

4. CONTRAINDICATIONS

Absolute Contraindications

• Patient refusal of regional anaesthesia (absolute; adamant refusal by patient or guardian)
• Allergy / known hypersensitivity to the specific local anaesthetic agent (ester class - true allergy is more common; amide allergy is rare but documented)
• Injection into infected tissue or skin at the proposed site (risk of spreading infection, reduced drug efficacy due to low pH in inflamed tissue)
• Bupivacaine IV (intravenous regional technique): absolutely contraindicated due to severe cardiotoxicity

Relative Contraindications

• Systemic coagulopathy / anticoagulation therapy: risk of haematoma, especially with deep blocks and neuraxial techniques (follow ASRA guidelines)
• Pre-existing neurological disease at the site of block: risk of compounding existing deficits; document baseline carefully and discuss risks
• Cardiovascular disease (for adrenaline-containing solutions): hypertension, cardiac arrhythmia, coronary artery disease
• Patients on monoamine oxidase inhibitors (MAOIs) or tricyclic antidepressants: avoid adrenaline-containing local anaesthetic solutions
• End-arterial locations (for adrenaline): fingers, toes, penis, nose, earlobes, pinna - risk of ischaemia and gangrene
• Contaminated wounds (for adrenaline): increased infection risk due to reduced blood flow
• Thyrotoxicosis / diabetes / peripheral vascular disease: exaggerated vasoconstrictor response to adrenaline
• Marginal skin flap viability: adrenaline risks flap ischaemia
• Uncooperative or agitated patients: inability to maintain still for nerve block or wound exploration

5. COMPLICATIONS

Local Complications

Systemic Complications (Local Anaesthetic Systemic Toxicity - LAST)

• Tinnitus, metallic taste in mouth, perioral numbness
• Malaise, light-headedness
• Dysarthria, diplopia
• Confusion, agitation

• Loss of consciousness
• Generalised tonic-clonic seizures

• Palpitations, bradycardia or tachycardia
• Conduction disorders: QRS widening, AV block
• Torsades de pointes
• Ventricular fibrillation
• Cardiac arrest / asystole

6. MANAGEMENT OF COMPLICATIONS

Management of LAST (Local Anaesthetic Systemic Toxicity)

1. Stop injection immediately
2. Call for help - this is a life-threatening emergency
3. Airway: secure airway with 100% oxygen; early intubation prevents hypoxia and acidosis (both worsen cardiotoxicity)
4. Venous access if not already established
5. Monitoring: ECG, pulse oximetry, BP

• Benzodiazepines (midazolam 0.05-0.1 mg/kg IV) are first-line for seizure control
• Propofol may be used cautiously in small doses if haemodynamically stable (avoid in cardiovascular compromise)
• Thiopentone to abort prolonged seizures

• Begin CPR with standard chest compressions
• Epinephrine: use titrated (small incremental) doses rather than large fixed boluses; 1-2 mcg/kg incremental boluses
• Avoid: vasopressin, calcium channel blockers, beta-blockers, lidocaine (as antiarrhythmic)
• For ventricular fibrillation: defibrillation (standard energy in adults; 2-4 J/kg in children)

• Mechanism: "lipid sink" - Intralipid sequesters lipophilic local anaesthetic away from cardiac sodium channels; also improves cardiac energy metabolism; decreases cardiac bupivacaine concentration by ~11% within 3 minutes
• Dose (adult): 20% Intralipid 1.5 mL/kg IV bolus, then infusion at 0.25 mL/kg/min for at least 10 minutes after cardiovascular stability is achieved; can repeat bolus up to 3 mL/kg total if no response
• Dose (paediatric): 2-5 mL/kg IV bolus; may repeat up to 10 mL/kg
• Should be available wherever major conduction blocks or large-volume infiltrations are performed
• NOT a substitute for careful technique - it is an acute resuscitation tool only
• Intralipid is most effective for bupivacaine toxicity

• Methylene blue 1-2 mg/kg IV over 5 minutes
• Provides reducing agent to convert methaemoglobin back to haemoglobin

Management of Local Complications

• Haematoma: apply pressure; monitor for expanding haematoma compressing nerves; rarely requires surgical evacuation
• Infection: empirical antibiotics; drainage if abscess forms; be vigilant for deep space spread (fever, limited hip movement, pelvic/back pain after pudendal block - may be life-threatening)
• Nerve damage: document baseline; conservative management; physiotherapy; most resolve within weeks to months; EMG/NCS if persistent
• Phrenic nerve palsy: supplemental oxygen; patients with compromised respiratory reserve may require respiratory support
• Failed block: supplement with additional infiltration, alternative regional technique, or proceed to general anaesthesia

Prevention of Complications

• Always aspirate before injection (negative aspiration does not exclude intravascular placement 100% of time)
• Use incremental, fractionated dosing for major blocks
• Use lowest effective concentration and volume
• Ultrasound guidance reduces vascular puncture and toxicity rates
• Add epinephrine as a test dose marker (tachycardia within 30 seconds suggests intravascular placement)
• Resuscitation equipment, oxygen, and appropriately skilled personnel must always be immediately available
• 20% Intralipid must be stocked wherever major blocks are performed

Medicines to Avoid Fertilisation After Ovulation (Emergency Contraception)

Important clarification: The question asks about post-ovulation contraception. It is important to understand that most emergency contraceptive (EC) medicines work by delaying or inhibiting ovulation - they are most effective before ovulation occurs. Once ovulation has already happened, their effectiveness drops significantly. This is a key clinical fact explained below under each drug.

Overview

1. Levonorgestrel (LNG) - Progestin-Only Pill

• Single dose: 1.5 mg (preferred - simpler and equally effective)
• Two-dose regimen: 0.75 mg, repeated 12 hours later (FDA-approved but less convenient)

• Labeled for use up to 72 hours after intercourse
• Can be extended to up to 120 hours (WHO recommendation), but effectiveness declines after 72 hours

• Primary action: delays or inhibits ovulation (delays the LH surge)
• Research by Noe et al. established that levonorgestrel only works if administered before the day of ovulation
• No pregnancies occurred in 87 women who received LNG 1-5 days before ovulation
• 7 pregnancies occurred in 35 women treated on the day of ovulation or after
• It is NOT an abortifacient - it has no effect once fertilisation has occurred

• Nausea (23% vs 50% with estrogen combinations)
• Vomiting (5.6%)
• Irregular menstrual bleeding (resolves within 1 month without treatment)
• Headache

• Significantly reduced effectiveness in women with BMI >30
• Total plasma concentration of LNG is significantly lower in obese women
• For obese women, ulipristal is preferred over levonorgestrel

2. Ulipristal Acetate (UPA) - Progesterone Receptor Modulator

• Delays follicular rupture - when ovulation is imminent (pre-LH peak), UPA delays the preovulatory follicle rupture for 5 days or more
• More effective than LNG at the periovulatory phase (when ovulation is imminent)
• When administered prior to the LH peak, it is 42% more effective than LNG at 72 hours, and 65% more effective in the first 24 hours
• Like LNG, it is not an abortifacient

3. Combined Oral Contraceptive (Yuzpe Regimen) - Now Largely Obsolete

• Much higher rates of nausea (50.5% vs 23.1% with LNG alone)
• Much higher rates of vomiting (18.8% vs 5.6%)
• Several case reports of thrombotic events (not seen with LNG alone)
• Inferior efficacy: pregnancy rate 3.2% vs 1.1% with LNG alone (RR 0.32)
• Replaced by LNG alone and then ulipristal

4. Copper Intrauterine Device (Cu-IUD) - Most Effective Method

• Effective within 5 days of intercourse (essentially 100% effective)
• Also effective up to 7 days after intercourse

• Inhibits sperm function (copper ions are spermicidal)
• Inhibits transport of fertilised egg
• Likely inhibits implantation
• Does not require pre-ovulatory timing - works even after ovulation and potential fertilisation (this makes it the most effective EC option post-ovulation)

• Pregnancy rate in the multicenter Wu et al. trial: 0 pregnancies in 1,893 women at follow-up
• Efficacy ~100% when inserted within 5 days

• Most effective EC available
• Also provides ongoing long-term contraception (94% of women continued using it at 12 months)
• Not affected by body weight

• Requires a clinic visit and a qualified provider for insertion
• 1/1,000 risk of uterine perforation
• Uterine cramping after insertion
• Not suitable for women with contraindications to IUD (active pelvic infection, uterine abnormalities, allergy to copper/Wilson's disease)

Summary Comparison Table

Critical Clinical Point