Surgery & Perioperative/Local anaesthetic

Local anaesthetics

also: lidocaine · bupivacaine · LA toxicity · lignocaine

Overview

Reversible nerve conduction block for local/regional anaesthesia. The maximum doses and LA systemic toxicity are the safety essentials.

Mechanism

Block voltage-gated sodium channels on the internal axonal membrane → prevent depolarisation/action-potential propagation → loss of sensation. Adding adrenaline causes vasoconstriction → prolongs action and allows a higher max dose (but never use adrenaline-containing LA in end-arterial fields: digits, nose, penis).

Indications

Local infiltration, nerve/regional blocks, spinal/epidural, topical

The agents

Lidocaineamide, fast/short

max 3 mg/kg (7 with adrenaline)

Rapid onset; also an antiarrhythmic.

Bupivacaineamide, slow/long

max ~2 mg/kg

Long-acting; the most CARDIOTOXIC — never IV; not for IVRA/Bier's block.

Adverse effects

LA systemic toxicity (LAST)serious

Perioral tingling/tinnitus → seizures → cardiac arrest. Treat with IV lipid emulsion (Intralipid).

Cardiotoxicity (bupivacaine)serious

Methaemoglobinaemia (prilocaine)common

Cautions & contraindications

Adrenaline-containing LA in end-arterial sites (digits, nose, penis, pinna)all

Ischaemic necrosis.

Exceeding the weight-based maximum doseall

LAST.

IV bupivacaine / bupivacaine for Bier's blockall

Fatal cardiotoxicity.

Interactions

Additive with antiarrhythmics

Monitoring & kinetics

Calculate max dose by weight; monitor for LAST signs,Intralipid available where regional blocks performed

Infiltration/regional/topical. Onset/duration vary by agent + adrenaline.

Source: BNF — Local anaesthesia