Which statement about vasoconstrictors used with local anesthetics is true?

• A. They shorten duration
• B. They have no effect
• C. They extend duration by constricting blood vessels
• D. They should never be used with local anesthetics

Answer: (C)

Vasoconstrictors added to local anesthetics extend the numbness by narrowing blood vessels at the injection site. This reduced blood flow slows the drug’s absorption into the bloodstream, so the anesthetic stays near the nerve longer and continues to block nerve signals for a longer period. The slower uptake also lowers the risk of surrounding tissue toxicity and helps keep the area numb during procedures. In addition, the decreased bleeding from vasoconstriction improves the working field. So, the idea that they extend duration by constricting blood vessels is the true point. While they are beneficial in many situations, they aren’t universally used in every patient—care is taken with individuals who have certain cardiovascular conditions or other risk factors.