What is the main side effect of local anesthetic systemic toxicity (LAST)?

The main side effect of local anesthetic systemic toxicity (LAST) is characterized by CNS excitability followed by depression. This phenomenon occurs due to the neurotoxic effects of local anesthetics when they enter the systemic circulation in significant amounts.

Initially, the excitatory phase might manifest as symptoms like dizziness, tinnitus, agitation, or seizures, reflecting increased neuronal excitability in the central nervous system. If the exposure continues or worsens, the excitatory phase transitions to a depressive phase, which can lead to symptoms such as drowsiness, confusion, and ultimately respiratory failure or coma due to the inhibitory effects of the anesthetics on neuronal function.

Cardiac arrhythmias, while a significant concern in LAST, are typically secondary to CNS effects and are not the defining or initial manifestation of the condition. Respiratory depression can result from profound CNS depression but does not represent the primary side effect. Allergic reactions are rare and generally unrelated to the dose or systemic toxicity of local anesthetic agents, focusing more on hypersensitivity rather than systemic toxic effects. Thus, the progression from excitability to depression stands out as the hallmark of LAST, making it a key consideration in understanding the pharmacological impact of local anesthetics.