Local anaesthetic systemic toxicity (LAST)
Introduction
Local anaesthetic systemic toxicity (LAST) is an uncommon but potentially life‑threatening complication of local anaesthetic (LA) administration. Presentations range from prodromal sensory symptoms (perioral numbness, tinnitus) through seizures and respiratory depression to refractory cardiovascular collapse.
Emergency clinicians must recognise early signs, stop further LA exposure, begin supportive/resuscitation measures modified for LAST, and initiate intravenous lipid emulsion promptly for severe cardiotoxicity.
Departments performing regional anaesthesia must have protocols, training and immediate access to 20% lipid emulsion (Intralipid) and local guidance (NPIS/TOXBASE) (RCEM/NPIS; Resuscitation Council UK).
Pathophysiology and risk factors
Local anaesthetics block voltage‑gated sodium channels. At high systemic concentrations they inhibit cortical, brainstem and myocardial sodium channels causing the characteristic CNS and cardiovascular manifestations.
Key predisposing factors include:
- Absolute overdose: total dose above the recommended maximum.
- Relative overdose, including:
- inadvertent intravascular injection, the most common cause of immediate LAST;
- rapid absorption from highly vascular sites such as the scalp, intercostal space, neck and deep blocks;
- failure to reduce dose in elderly patients, low body weight, hepatic impairment, malnutrition or heart failure.
- Drug factors:
- bupivacaine and levobupivacaine have greater cardiotoxicity risk than lignocaine;