Which statement about vasoconstrictors in local anesthetics is true?

Which statement about vasoconstrictors in local anesthetics is true?

• A. Vasoconstrictor increases systemic absorption
• B. Vasoconstrictor decreases duration of anesthesia
• C. Vasoconstrictor has no effect on localization
• D. Vasoconstrictor localizes by reducing blood flow

Answer: (D)

Vasoconstrictors added to local anesthetics work by constricting blood vessels at the injection site. This reduced blood flow slows the removal of the anesthetic into the bloodstream, so more of the drug stays locally where it was injected. That keeps a higher concentration of anesthetic at the nerve site for longer, which both prolongs the duration of anesthesia and helps minimize bleeding during the procedure. Among the statements, the one that describes localization by reducing blood flow best fits this mechanism. The other ideas conflict with how vasoconstrictors actually work: they do not increase systemic absorption, they do affect localization by keeping the drug at the site longer, and they generally increase—not decrease—the duration of anesthesia.

Vasoconstrictors added to local anesthetics work by constricting blood vessels at the injection site. This reduced blood flow slows the removal of the anesthetic into the bloodstream, so more of the drug stays locally where it was injected. That keeps a higher concentration of anesthetic at the nerve site for longer, which both prolongs the duration of anesthesia and helps minimize bleeding during the procedure. Among the statements, the one that describes localization by reducing blood flow best fits this mechanism. The other ideas conflict with how vasoconstrictors actually work: they do not increase systemic absorption, they do affect localization by keeping the drug at the site longer, and they generally increase—not decrease—the duration of anesthesia.