What are the manifestations of local anesthetic systemic toxicity (LAST)?

Manifestations of Local Anesthetic Systemic Toxicity (LAST)

Local anesthetic systemic toxicity (LAST) typically presents with a biphasic pattern of central nervous system (CNS) symptoms followed by cardiovascular collapse, though approximately 40% of cases may present atypically with isolated cardiovascular symptoms or delayed onset. 1, 2

CNS Manifestations (77-89% of LAST cases)

Early CNS Signs and Symptoms

• Circumoral numbness and facial tingling
• Metallic taste
• Slurred or pressured speech
• Auditory changes and tinnitus
• Visual disturbances
• Lightheadedness and dizziness
• Confusion and disorientation
• Agitation and excitation
• Hallucinations

Progressive CNS Manifestations

• Seizures (most common CNS manifestation)
• Obtundation and loss of consciousness
• CNS depression
• Respiratory arrest

Cardiovascular Manifestations (32-55% of LAST cases)

Early Cardiovascular Signs

• Hypertension
• Tachycardia
• Premature ventricular contractions

Progressive Cardiovascular Manifestations

• Conduction disturbances
• Bradycardia
• Wide-complex tachycardia
• Ventricular fibrillation (13% of cases)
• Asystole (12% of cases)
• Hypotension
• Cardiogenic shock
• Cardiac arrest with refractory resuscitation

Atypical Presentations

Approximately 40% of LAST cases do not follow the classic pattern and may present with:

• Isolated cardiovascular symptoms without CNS manifestations (20% of cases)
• Delayed onset of symptoms after local anesthetic administration
• Variable progression of symptoms

Risk Factors for LAST

• Patient factors:

  • Extremes of age (especially infants)
  • Decreased liver function
  • Low cardiac output
  • Pregnancy
  • Pre-existing cardiac disease

• Drug factors:

  • Higher potency local anesthetics (bupivacaine > ropivacaine > lidocaine)
  • Higher doses and concentrations
  • Rapid absorption

• Technical factors:

  • Inadvertent intravascular injection
  • Highly vascular injection sites

Clinical Implications

The biphasic presentation of LAST has important clinical implications:

1. Early recognition of prodromal CNS symptoms may allow intervention before cardiovascular collapse occurs
2. Isolated cardiovascular symptoms without preceding CNS manifestations can occur in approximately 20% of cases
3. The incidence of LAST is estimated at 0.87 per 1,000 patients receiving peripheral nerve blocks 1

Prevention Strategies

• Use ultrasound guidance for regional anesthesia techniques
• Administer the lowest effective dose of local anesthetic
• Use incremental dosing with frequent aspiration tests
• Consider adding epinephrine (10-15 μg) as an intravascular marker
• Continuous neurologic and cardiovascular monitoring during administration
• Consider using less cardiotoxic agents (ropivacaine or levobupivacaine instead of bupivacaine)

Treatment Approach

1. Stop local anesthetic administration immediately if LAST is suspected
2. Call for help and prepare for potential cardiovascular collapse
3. Secure airway and administer 100% oxygen
4. Treat seizures with benzodiazepines (Class 1 recommendation, LOE C-LD) 1
5. Administer 20% intravenous lipid emulsion for LAST (Class 1 recommendation, LOE C-LD) 1
6. Consider sodium bicarbonate for wide-complex tachycardia (Class 2a, LOE C-LD) 1
7. Consider atropine for significant bradycardia (Class 2a, LOE C-EO) 1
8. Consider VA-ECMO for refractory cardiogenic shock (Class 2a, LOE C-EO) 1

Early recognition and prompt treatment of LAST are essential to prevent progression to cardiovascular collapse and improve outcomes. Healthcare providers administering local anesthetics should be familiar with the full spectrum of LAST manifestations, including atypical presentations.