PH2.5 | PH2.5 | Local Anaesthetics and Administration Techniques — SDL Guide — Summary & Reflection

KEY TAKEAWAYS

Local anaesthetics block voltage-gated Na⁺ channels, preferentially stabilising the inactivated state to prevent action potential propagation. They are classified as esters (procaine, cocaine, chloroprocaine, benzocaine — plasma hydrolysis, PABA metabolite, higher allergy risk) or amides (lignocaine, bupivacaine, ropivacaine, prilocaine, mepivacaine — hepatic metabolism, rare allergy). Onset is governed by pKa (lower pKa → faster), duration by protein binding (higher → longer), potency by lipid solubility (higher → more potent but more cardiac toxic). Maximum doses: lignocaine 3 mg/kg plain / 7 mg/kg with adrenaline; bupivacaine 2 mg/kg (NEVER in Bier's block). Systemic toxicity: tinnitus → seizures → cardiac arrest; bupivacaine cardiac toxicity is refractory — treat with lipid emulsion 1.5 mL/kg IV. Administration methods: topical, infiltration, peripheral nerve block, Bier's block (lignocaine only), epidural (catheter, bupivacaine/ropivacaine), spinal (hyperbaric bupivacaine). Adrenaline 1:200,000 prolongs block — contraindicated in end-artery tissues (digits, nose, penis, ear, penis).

REFLECT

The hook case — a patient developing tinnitus and then a seizure during lignocaine infiltration — was a preventable adverse event. Think about what safeguards you would put in place if you were responsible for LA administration in an emergency department. How would you ensure: (1) the dose was calculated before injection, not after; (2) tinnitus and perioral tingling are recognised immediately as early toxicity (rather than dismissed as 'normal')?; (3) lipid emulsion is immediately available wherever bupivacaine is used in your institution? These are systems-thinking questions, not just pharmacology questions. Patient safety in LA practice is built on protocols, checklists, and drug preparation habits — not just drug knowledge. What habit will you adopt from this module that was not already part of your routine?