Many of us learned to anesthetize the scrotal skin and vasa using a 25 or 27-gauge needle, and this does work. A smaller 30-gauge needle, though, can increase patient comfort and minimize hematomas.
Below are diagrams showing how to place the anesthesia into the skin and onto the vas deferens.
For the initial anesthesia of the skin, the needle is placed quite superficially into the skin of the median raphe.
A small wheal is formed using approximately 0.5 to 1cc of lidocaine. This numbs the skin.
Then the needle is inserted at a 90 degree angle to the skin, directly downwards until the tip is gently placed directly onto the vas. The goal is to inject into the space between the vas and the thin layer of perivasal fascia enveloping the vas.
Approximately 1cc is enough as long as the anesthetic is placed into the proper location. Sometimes you can even feel a small temporary swelling on the vas as the anesthetic goes in. After the injection into the space around the vas, the anesthetic diffuses both cephalad and caudally to anesthetize several centimeters of vas deferens.
