Q: I have read about something called “tumescent anesthesia” but didn’t understand what it is. What exactly is it? — S.S., Hoboken, N.J.

A: Tumescent techniques were first popularized in liposuction surgery where large quantities of fluid containing adrenalin were injected into the person’s fat layer to decrease bleeding before the fat was literally sucked out of the body. Bleeding was minimized because the epinephrine (adrenaline) constricted blood vessels and the fluid compressed the blood flow in the smallest blood vessels called capillaries.

The technique allowed small liposuction procedures to be performed safely as an out-patient procedure. In surgical hair restoration, low concentrations of anesthetic fluid and adrenaline are injected into the fat layer in the back of the scalp.

In a hair transplant, besides decreasing the bleeding, the fluid makes the skin more rigid so that the incision can be more easily made without cutting hair follicles. It also helps the doctor avoid damage to the deeper blood vessels and nerves in the scalp.