How are femoral and sciatic nerve blocks performed? Which local anesthetic agents would you use?
There is no one way to perform these blocks. There are variations in all the parameters and how a block is per-formed is usually user-dependent. The reader is directed to the suggested reading list for more details about these blocks. The following is this author’s preferred method for performing these blocks.
With the patient in the supine position, the femoral artery is palpated. Approximately 1–2 cm below the inguinal ligament and lateral to the artery a 2 inch needle attached to a nerve stimulator set at 1.5 milliamps is inserted. The needle is slowly advanced until a quadriceps twitch or a “patella snap” is elicited. The nerve stimulator is lowered to 0.4 milliamps and if the “patella snap” is still present, local anesthetic is injected.
With the patient in the lateral decubitus position (oper-ative side up), a line is drawn between the greater trochanter and posterior superior iliac spine. A 5 cm line is drawn perpendicularly caudad from the midpoint of this line. At this point, a 4 or 6 inch needle attached to a nerve stimulator set at 1.5 milliamps is inserted and is advanced until a hamstring twitch or any motor movement in the foot is elicited. Local anesthetic is injected when the twitch is still present at less than 0.4 milliamps.
The choice of local anesthetic will be dependent on the length of the procedure, the quickness of the surgeon, whether a catheter will be placed, the toxicity of each local anesthetic, and the user’s preference. One option for either of the above-described blocks is to use 30 cc of ropivacaine 0.5% with epinephrine 1:200,000. This provides for a long duration of anesthesia and, while the onset may not be as quick as with mepivacaine, there is usually sufficient time from when the block is performed to surgical incision for the anesthetic to take effect.