Local Anaesthetics & Toxicity
Local anaesthetics (LAs) are among the commonest drugs used in the emergency department for wound infiltration, field blocks and minor procedures.
They act by reversible blockade of fast voltage‑gated sodium channels and, when absorbed systemically or injected intravascularly, can cause life‑threatening central nervous system (CNS) and cardiovascular (CVS) toxicity - local anaesthetic systemic toxicity (LAST).
This section summarises the pharmacology most relevant to acute care, recognition of LAST, immediate management (including the recommended lipid emulsion regimen), and departmental preparedness.
Mechanism and clinical relevance
- Mechanism: LAs stabilise the inactivated state of voltage‑gated Na+ channels in excitable membranes, preventing action‑potential initiation and propagation.
- Why toxicity occurs: Excessive systemic absorption or inadvertent intravascular injection allows blockade of sodium channels in the CNS and myocardium. CNS signs often precede CVS collapse, but severe cardiovascular toxicity can occur rapidly and unpredictably.
Common local anaesthetics used in the ED
Confirm exact preparations and dosing with your local drug chart, BNF or SmPC.
Routes and practical points
- Topical and subcutaneous infiltration are common; for central line procedures local infiltration (usually lidocaine) is preferred.
- Adding adrenaline reduces systemic uptake and prolongs duration but is contraindicated in some anatomical sites - check local guidance.