What is local anesthetic (LA) toxicity?
A systemic toxic reaction that occurs when plasma concentration of an LA exceeds the safe threshold, affecting the CNS and CVS
It usually results from overdose, rapid absorption, or inadvertent intravascular injection.
What are the primary causes of LA toxicity?
- Inadvertent intravascular injection of LA
- Administration of excessive total dose
- Rapid absorption from highly vascular sites
- Impaired metabolism or excretion
- Drug interactions
E.g., β-blockers and cimetidine reduce lidocaine metabolism.
What are the risk factors for LA toxicity?
- Extremes of age (infants, elderly)
- Hepatic dysfunction
- Renal dysfunction
- Cardiac disease
- Pregnancy
- High vascularity of injection site
These factors can enhance sensitivity or impair clearance.
What is the pathophysiology of CNS toxicity due to LA?
LA blocks inhibitory neurons first, leading to unopposed excitatory activity, seizures, and later widespread depression (coma, respiratory arrest).
What is the pathophysiology of CVS toxicity due to LA?
Direct myocardial depression, conduction block, and vasodilation, with bupivacaine having a high affinity for cardiac Na⁺ channels, leading to severe ventricular arrhythmias.
What are the early CNS manifestations of LA toxicity?
- Circumoral numbness
- Tongue paresthesia
- Dizziness
- Tinnitus
- Blurred vision
- Metallic taste
What are the intermediate CNS manifestations of LA toxicity?
- Tremors
- Agitation
- Confusion
- Seizures
What are the late CNS manifestations of LA toxicity?
- CNS depression
- Drowsiness
- Coma
- Respiratory arrest
What are the cardiovascular manifestations of LA toxicity?
- Hypotension
- Bradycardia
- Conduction abnormalities
- Ventricular arrhythmias
- Cardiovascular collapse
What investigations are recommended for LA toxicity?
- Monitoring: ECG, BP, SpO₂, EtCO₂
- ABG: metabolic acidosis, hypoxemia, hypercarbia
- Serum LA levels (for research, not practical intraoperatively)
What are the signs of intraoperative recognition of LA toxicity?
- Sudden CNS signs (tinnitus, metallic taste, seizures)
- Sudden bradycardia, hypotension, arrhythmias following regional anesthesia
What is the immediate action to take in case of LA toxicity?
- Stop LA administration
- Call for help
- Provide 100% oxygen
- Secure airway and ventilate if needed
- Monitor ECG, BP, SpO₂
What is the specific treatment for seizures due to LA toxicity?
- Midazolam 2–4 mg IV bolus
- Diazepam 0.1 mg/kg IV
Avoid large doses of propofol as it can worsen CV depression.
What is the treatment protocol for cardiovascular collapse due to LA toxicity?
- Follow ACLS protocol
- Administer epinephrine 10–100 mcg IV bolus
- Use vasopressors like noradrenaline if refractory
- Amiodarone for arrhythmias
Avoid lidocaine and procainamide as they worsen toxicity.
What is the bolus and infusion dosage for 20% Intralipid therapy in LA toxicity management?
- Bolus: 1.5 mL/kg IV over 1 min
- Infusion: 0.25 mL/kg/min IV
- Max dose: 12 mL/kg in 30 min
What are the complications associated with LA toxicity?
- Prolonged seizures
- Refractory ventricular arrhythmias
- Cardiac arrest
- Aspiration pneumonia due to seizures or CNS depression
What is the prognosis for LA toxicity with early recognition?
Good outcome with intralipid therapy, but bupivacaine-induced toxicity has higher severity and mortality.
Fill in the blank: Always use a _______ with adrenaline to detect intravascular injection.
test dose
What are some anesthetic considerations to reduce the risk of LA toxicity?
- Use the lowest effective dose of LA
- Aspirate before injecting
- Incremental injection instead of full bolus
- Ultrasound-guided blocks
What is the dosage of amiodarone for arrhythmias in LA toxicity?
300 mg IV for arrhythmias
