Final answer:
Local anesthetics like Lidocaine cause numbness by blocking voltage-gated sodium channels, preventing action potential propagation. Systemic toxicity primarily affects the CNS before the CVS. Special electrical safety measures are needed to prevent ventricular fibrillation during surgery.
Step-by-step explanation:
Systemic Toxicity of Local Anesthetics
Local anesthetics are drugs used to temporarily block nerve conduction to specific areas of the body, leading to a loss of sensation in those regions. Lidocaine, for example, is a commonly used local anesthetic that works by blocking voltage-gated sodium channels on nerve cells. By preventing the influx of sodium ions, these drugs inhibit the propagation of action potentials along nerves, which is essential for sensation and muscle contraction. As voltage-gated sodium channels are blocked, signals responsible for pain and sensation cannot traverse the nerve pathways, leading to numbness.
Systemic toxicity can occur if a significant amount of the local anesthetic enters the systemic circulation. Toxic effects most commonly affect the central nervous system (CNS) and, less frequently, the cardiovascular system (CVS). Symptoms of CNS toxicity include tingling around the mouth, tinnitus, tremors, and eventual progression to seizures. CVS effects may include hypotension, heart block, and even ventricular fibrillation, a potentially fatal arrhythmia. However, CNS effects typically precede CVS effects.
Special precautions in electrical safety are critical because even a small voltage applied directly to the heart, such as 20.0 μA flowing through a resistance of 300Ω, could result in ventricular fibrillation. This emphasizes the importance of strict adherence to safety protocols during procedures involving electrical equipment near the heart to prevent life-threatening cardiovascular complications.