Local Anaesthetic Toxicity
OVERVIEW
- sodium channel blockade -> arrhythmias and neurotoxicity
CAUSES
- drug overdose
- IV injection
- rapid absorption from highly vascular areas
- accumulation of multiple injections or infusion
PREVENTION
- know your maximum doses
- aspiration before injecting
- small, divided doses
- inject slowly & ask about symptoms
- increased LA effect in – acidosis, hypoxia, hypercarbia
CLINICAL FEATURES
CNS
Excitation phase
- numbness of tongue and circumoral tissue
- restlessness
- tinnitus
- vertigo
- shivering
- muscular twitching & tremors (initially involving muscles of face & distal parts of extremities)
- generalised convulsions
Depression phase
- generalised depression
- decreased LOC
- apnoea
- precise site for LA-induced seizures is not known.
CVS
Initial
- hypertension & tachycardia
Then
- peripheral vasodialatation, profound hypotension -> decreased Q
- sinus bradycardia, intracardiac conduction defects (prolonged PR & QRS complex), ventricular arrhythmias, cardiac arrest.
MANAGEMENT
Goals
(1) limit LA exposure
(2) prolonged normal resuscitation
(3) consider lipid emulsion administration
(4) prevention of acidosis
Mild symptoms – midazolam boluses IV (raises seizure threshold)
Stop injecting or infusion!
Call for help
- A – ETT
- B – FiO2 1.0, hypertentilate (avoid acidosis -> HCO3- 1mmol/kg)
- C – defibrillation, CPR, fluid, inotropes, amiodarone 5mg/kg, bretylium 5-10mg/kg LD -> 1-2mg/min
- D – midazolam, propofol, thiopentone
Lipid emulsion (20% intralipid)
- 1 mL\kg (over 1min) q3min x 3 then
- Infusion 0.25mL\kg\min
Important points
- continue CPR to distribute
- repeat bolus every 3 min up to 3mL\kg total dose until circulation restored
- continue infusion until haemodynamic stability restored
- increase rate to 0.5mL\kg\min if BP declines
- maximum total dose = 8mL\kg
70kg Adult
- 500mL bag of Intralipid 20%
- 70mL bolus stat x3
- infuse rest of bag over 15 minutes
Lipid Emulsion Mechanism
- ?
- lipid sink model – draws LA out of plasma
- may actually facilitate redistribution of LA from target organs to fat stores
- it may overwhelm the inhibition of the translocase by mass action -> increases myocardial energy supply
References and Links
CCC Toxicology Series
General
Approach to acute poisoning, ECGs in Tox, Evidenced-based Tox, Toxicology literature summaries, Does anti-venom work?
Toxins / Overdose
Amphetamines, Barbituates, Benzylpiperazine, Beta Blockers, Calcium Channel Blocker, Carbamazepine, Carbon Monoxide, Ciguatera, Citrate, Clenbuterol, Cocaine, Corrosive ingestion, Cyanide, Digoxin, Ethanol, Ethylene Glycol, Iron, Isoniazid, Lithium, Local anaesthetic, Methanol, Monoamine oxidase inhibitor (MAOI), Mushrooms (non-hallucinogenic), Opioids, Organophosphate, Paracetamol, Paraquat, Plants, Polonium, Salicylate, Scombroid, Sodium channel blockers, Sodium valproate, Theophylline, Toxic alcohols, Tricyclic antidepressants (TCA)
Envenomation
Marine, Snakebite, Spider, Tick paralysis
Syndromes
Alcohol withdrawal, Anticholinergic syndrome, Cholinergic syndrome, Drug withdrawals in ICU, Hyperthermia associated toxidromes, Malignant hyperthermia (MH), Neuroleptic malignant syndrome (NMS), Opioid withdrawal, Propofol Infusion Syndrome (PrIS) Sedative toxidrome, Serotonin syndrome, Sympatholytic toxidrome, Sympathomimetic toxidrome
Decontamination
Activated Charcoal, Gastric lavage, GI Decontamination
Enhanced Elimination
Enhanced elimination, Hyperbaric therapy for CO
Antidotes
Antidote summary, Digibind, Glucagon, Flumazenil, HIET – High dose euglycaemic therapy, Intralipid, Methylene Blue, N-Acetylcysteine (NAC), Naloxone
Miscellaneous
Cocaine chest pain, Digoxin and stone heart theory, Hyperbaric oxygen, Hypoxaemia in tox, Liver failure in tox, Liver transplant for paracetamol, Methaemoglobinaemia, Urine drug screen
- Flashcard – Local anesthetic toxicity
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at The Alfred ICU, where he is Deputy Director (Education). He is a Clinical Adjunct Associate Professor at Monash University, the Lead for the Clinician Educator Incubator programme, and a CICM First Part Examiner.
He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives. He was one of the founders of the FOAM movement (Free Open-Access Medical education) has been recognised for his contributions to education with awards from ANZICS, ANZAHPE, and ACEM.
His one great achievement is being the father of three amazing children.
On Bluesky, he is @precordialthump.bsky.social and on the site that Elon has screwed up, he is @precordialthump.
| INTENSIVE | RAGE | Resuscitology | SMACC
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Great summary.
I was interested to know the source/reference of your intra-lipid doses as it varies (lower) than most other suggested doses of 1.5ml/kg see:
Management of severe local anaesthetic toxicity