What is the first sign of local anesthesia toxicity?

First Signs of Local Anesthesia Toxicity

The first signs of local anesthetic systemic toxicity (LAST) typically manifest as central nervous system excitement, with patients experiencing circumoral numbness, facial tingling, pressured or slurred speech, metallic taste, auditory changes, and hallucinations, which may also be accompanied by hypertension and tachycardia. 1

Clinical Presentation of LAST

LAST follows a predictable progression of symptoms, though there is significant interpatient variability:

Initial CNS Manifestations

• Circumoral numbness and facial tingling are often the earliest warning signs 1
• Pressured or slurred speech occurs as toxicity progresses 1
• Metallic taste in the mouth is a characteristic early symptom 1
• Auditory changes and hallucinations may develop 1
• These early CNS symptoms may be accompanied by hypertension and tachycardia 1

Progression of Toxicity

• As toxicity evolves, patients may develop seizures or central nervous system depression 1
• Severe cases may progress to cardiac failure or arrest 1
• The biphasic nature of LAST typically begins with CNS excitation followed by inhibition 2

Risk Factors for LAST

Several factors increase the risk of developing local anesthetic toxicity:

• Patient factors: infants, patients with decreased liver function, and those with low cardiac output are more vulnerable 3
• Drug-related factors: higher doses, more potent agents (bupivacaine is more cardiotoxic than lidocaine) 4
• Technical factors: inadvertent intravascular injection, rapid absorption from highly vascular areas 3

Prevention Strategies

To minimize the risk of LAST:

• Use appropriate dosing: follow maximum recommended doses (7 mg/kg lidocaine with epinephrine, 4.5 mg/kg without epinephrine for adults) 1
• Employ dose fractionation: administer local anesthetics in small, divided doses 3
• Perform aspiration before injection to check for intravascular placement 3
• Consider using less toxic agents such as ropivacaine or levobupivacaine when appropriate 3
• Use ultrasound guidance for regional anesthetic techniques when available 5

Management of LAST

If LAST is suspected, follow this algorithm:

1. Stop administration of local anesthetic immediately 3
2. Call for help and alert nearest facility with cardiopulmonary bypass capability 1
3. Secure airway and administer 100% oxygen 1
4. Treat seizures with benzodiazepines (e.g., midazolam 0.1-0.2 mg/kg IV) 1
5. For cardiovascular symptoms:
   • Administer 20% lipid emulsion according to protocol 1
   • For adults >70 kg: initial bolus of 100 ml 6
   • For adults <70 kg or children: 1.5 ml/kg 6
   • Consider sodium bicarbonate for wide-complex tachycardia 1
   • Consider atropine for bradycardia 1

Important Considerations

• The incidence of LAST is estimated at 1-11 cases per 10,000 regional anesthesia procedures 3
• Anesthetic toxicity in the dermatologic setting is extremely rare due to typically lower doses used 1
• Bupivacaine is associated with more severe cardiac toxicity than other commonly used local anesthetics 4
• Early recognition of symptoms is critical as progression to cardiovascular collapse can occur rapidly 5
• Lipid emulsion therapy should be initiated at the first sign of serious systemic toxicity 6

Remember that while CNS symptoms typically appear first, approximately 20% of LAST cases present with isolated cardiovascular disturbances, making vigilance for atypical presentations essential 5.