Symptoms of Lidocaine Toxicity
Lidocaine toxicity presents with a predictable progression from early neurological symptoms (perioral numbness, tingling, tinnitus) to severe CNS manifestations (seizures, loss of consciousness) and ultimately life-threatening cardiovascular collapse (bradycardia, hypotension, cardiac arrest). 1, 2
Early Warning Signs (CNS Symptoms at Lower Plasma Concentrations)
Neurological symptoms appear before cardiovascular toxicity, making them the critical early warning system 2:
- Perioral numbness and tingling of tongue/lips 3, 1, 2
- Tinnitus (ringing in ears) 3, 1
- Light-headedness and dizziness 3, 1, 2
- Metallic taste 1
- Visual and auditory disturbances, including blurred or double vision 1, 4
- Nervousness, apprehension, or euphoria 1, 4
- Facial flushing 3
Intermediate CNS Manifestations
As plasma concentrations increase, excitatory symptoms develop 1, 4:
- Muscle twitching and tremors 3, 4
- Slurred speech 3
- Confusion and agitation 1, 4
- Drowsiness (often an early sign of high blood levels) 1, 4
- Restlessness 1
Severe CNS Toxicity
At higher concentrations, life-threatening neurological symptoms emerge 1, 4:
- Seizures/convulsions 3, 1, 4
- Loss of consciousness progressing to coma 3, 1
- Respiratory depression and arrest 3, 1, 4
Late Cardiovascular Manifestations
Cardiovascular symptoms typically occur at higher plasma concentrations than CNS symptoms (around 9-10 μg/mL) 1:
- Bradycardia 3, 1, 4
- Hypotension 3, 1, 4
- Wide-complex tachycardia (QRS prolongation) - a late sign 2
- Myocardial depression 3
- Cardiac arrhythmias 3
- Cardiovascular collapse leading to cardiac arrest (PEA or asystole) 3, 1, 4
Critical Clinical Pearls
The excitatory CNS manifestations may be very brief or absent entirely, in which case the first manifestation may be drowsiness merging directly into unconsciousness and respiratory arrest 4. This makes early recognition of subtle symptoms crucial.
Toxic symptoms can persist even after lidocaine concentrations decrease below therapeutic levels 5, requiring prolonged monitoring and supportive care.
Serious toxicity typically occurs at plasma levels of 9-10 μg/mL, though symptoms have been reported at therapeutic dosages with undetectable serum levels 1, 6, emphasizing that clinical presentation trumps laboratory values.