Toxicity happens from local anesthetics being given too fast, too much, or in the unintended spot
Systemic toxicity manifests first with neurologic symptoms like circumoral numbness, tinnitus, blurred vision, nausea, and even seizures. Severe toxicity can then progress to arrhythmias and cardiac arrest.
Maximum doses of lidocaine: 4 mg/kg; and with epinephrine: 7mg/kg.
Maximum dose of bupivacaine: 2mg/kg; with epinephrine 3mg/kg
Editor note: treat seizures with benzodiazepines and avoid propofol for sedation; severe toxicity can also be treated with a 20% lipid emulsion, though there is debate on its efficacy