Why doesn't local anesthesia spread to the whole body?

"Local" is why: "local" anesthesia does just that-a small dose of a numbing agent is injected near a nerve, that, when in a certain concentration, blocks impulses through that nerve. The result is numbness and weakness in the distribution of that nerve. This resolves as the local anesthetic is 'washed out" by blood and the localized concentration now will decrease-allowing the nerve to work again.

It does: All drugs sread out inside the body. Imagine a pinch of slat on ur finger. It will taste salty. Nwo spread over all ur body . No more salty taste. Increase the pinch a lot and it will be salty. To nmb a nurve just put a pinch near it. When it spreads out no more numb. Increase the dose 100x and the body is numb all over but first you get heart changes and seizures.

Placement: Local anesthetics are placed directly around nerves, or in limited areas of the body. Once placed there is no mechanism to transport the medications. To make it around the body a drug needs to be placed in the bloodstream.