When you feel that the needle tip is in the correct position and level, maintain your hand holding the syringe steady as you gently aspirate back (pull back on the plunger with your other hand), looking for blood entering the syringe.
Remember the dorsal artery is just medial to the dorsal nerve.
Also important: Avoid partially withdrawing the needle during aspiration!
The source of the blood is either from the dorsal artery (bright red) or from a skin vein (dark red). If blood is aspirated, completely withdraw the needle and apply direct pressure with a gauze sponge or alcohol swab to minimize formation of a hematoma. Arterial puncture will rapidly form a hematoma and will require longer direct pressure, 30 to 60 seconds. Reinsert the needle, making sure the needle tip stays just lateral to the previous puncture.
After aspiration without blood, and being careful not to move the needle tip deeper or shallower, infiltrate either 0.4 (40 units, down to the 60 unit mark) or 0.3ml (30 units, down to the 70 unit mark), depending on the total amount of 1% lidocaine being injected. Please see Preparation section and look at the calculation of lidocaine dose and general rule paragraph, if unsure.
Use two separate injections to inject the appropriate amount of 1% lidocaine. There is a one injection technique, but it may be more difficult to master the correct site of the second infiltration and there may be a higher risk of puncturing a vein or dorsal artery.
After completion of the infiltration and withdrawal of the needle, apply short-term pressure to any puncture site bleeding.