Local anesthetic systemic toxicity

Background

• Acronym: LAST
• Life-threatening adverse reaction to local anesthetic toxicity.
• Incidence = ~0.2% of nerve blocks
• Generally occurs within minutes of injection

Causes

• Injection of local anesthetic into systemic circulation
  • Most common source of toxicity
  • Intravascular injection can cause toxicity below the maximum recommended dose
• Exceeding the maximum dose of local anesthetic (see table below)
• Absorption of anesthetic into systemic circulation by injection into extremely vascular area.

Maximum Doses of Anesthetic Agents

Agent	Without Epinephrine	With Epinephrine	Duration	Notes
Lidocaine	5 mg/kg (max 300mg)	7 mg/kg (max 500mg)	30-90 min	1% soln contains 10 mg/ml 2% soln contains 20 mg/ml
Mepivicaine	7 mg/kg	8 mg/kg
Bupivicaine	2.5 mg/kg (max 175mg)	3 mg/kg (max 225mg)	6-8 hr	0.5% soln contains 5 mg/ml May cause cardiac arrest if injected intravascularly Do not buffer with bicarbonate
Ropivacaine	3 mg/kg
Prilocaine	6 mg/kg
Tetracaine	1 mg/kg	1.5 mg/kg	3hrs (10hrs with epi)
Procaine	7 mg/kg	10 mg/kg	30min (90min with epi)

Diphenhydramine as Local Anesthetic

• Injectable 1% diphenhydramine (10 mg/mL) can be used as a local anesthestic alternative to ester/amide anesthetics
  • Sodium channel blocker mechanism
  • 1-2 mL of 1% diphenhydramine at a time, to not exceed excessive sedation dose
  • Typical vial is 50 mg/mL, so to make 10 mg/mL:
    • 10 mL NS removed from 50 mL vial
    • Add 10 mL of 50 mg/mL diphenhydramine to 40 mL of NS
    • Sedation is dose related and is similar to what would be expected for IM doses
    • Relative contraindications are the same for IM diphenhydramine administration

Clinical Features

Clinical course tends to be a dose-dependant progression from CNS symptoms to CVS symptoms and death

• CNS symptoms
  • Agitation
  • Auditory changes/Tinnitus
  • Metallic taste
  • Slurred speech
  • Seizures or drowsiness
  • Coma
  • Respiratory arrest
• Cardiovascular
  • Early signs
    • Tachycardia
    • Ventricular dysrhythmia
    • Hypertension
  • Late signs
    • Bradycardia
    • Conduction block
    • Cardiovascular collapse
    • Asystole

Differential Diagnosis

• Anaphylaxis
• Anxiety
• Methemoglobinemia - local anesthestics oxidize Fe2+ to Fe3+ in Hb

Sodium Channel Blockade Toxidrome

• Phenothiazines
• Antihistamines
• Sotalol
• TCAs
• Antipsychotics
• Cocaine
• Anti-spasmodics, cyclobenzaprine
• Chloroquine
• Anti-malarials
• Class Ia and Ic antiarrhythmics
• Local anesthetic systemic toxicity
• Venlafaxine toxicity

Evaluation

• Clinical diagnosis

Workup

• Directed by clinical picture
• Blood levels of anesthetic are available, but not clinically useful.

Management

• Aggressive supportive care (including airway management) and application of ACLS
  • Ventilate with 100% FiO2 - bolus dose of 50-100mg IV succinylcholine paralyzes without depressing CNS or CV
  • Hypercapnia, hypoxia, acidosis all worsen toxic effects
  • Manage seizures with benzodiazepines; propofol is an option but may worsen cardiovascular toxicity
  • Temporary pacing may be required for symptomatic bradycardia
• Early activation of ECMO or consideration for transfer to ECMO center as cardiac arrest is often refractory to ACLS.
• 1 amp of sodium bicarbonate IV q2 min for:
• Vtach or VF
  • Severe acidosis
• Lipid emulsion, (Intralipid) 20% solution
  • Lipid sink, binds to local anesthetic
  • 1.5 mL/kg bolus over 1 minute
  • Then, 0.25 mL/kg/min for 20 min or until hemodynamic stability achieved
    • ↑ to 0.5 mL/kg/min if hemodynamic status declines
  • Maximum total dose 12 mL/kg.
  • Consider drawing extra blood as will interfere with labs
• ACLS modifications:
  • Avoid vasopressin
  • Avoid calcium-channel blockers and beta-blockers
  • Amiodarone preferred in ventricular dysrhythmias

Disposition

• Admit

See Also

• Local anesthetics
• Nerve blocks (main)
• Lidocaine
• Bupivicaine

External Links

• Medscape:Local Anesthetic Toxicity