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6 Tips for Better Peripheral Nerve Blocks
Steps you can take to localize the anesthetic to the site of surgery.
Tripti Kataria
Publish Date: October 10, 2007   |  Tags:   Anesthesia

Peripheral nerve blocks (PNB) have become more popular in recent years. Here are six tips to improve your regional anesthesia technique.

Patient selection.
Nerve blocks require patient cooperation. Is the patient's mental and emotional makeup appropriate? Often, patient education about the PNB procedure and its benefits along with reassurance from the anesthesia provider will put patients at ease and make them more amenable to the nerve block. A note here: If a patient requires a lot of supplemental sedation, the surgical procedure is long or the surgical positioning is uncomfortable, a combined PNB and general anesthesia may be a good option.

Safety first.
Before you perform PNBs, be prepared for emergencies that can arise from administering large doses of local anesthetics. Always place patients on monitors, including a non-invasive blood pressure cuff and pulse oximetry before you begin a PNB. (See "What's New in Patient Monitors" on page 39.) Is airway equipment readily available to secure the airway and hyperventilate the patient in the event of an intravascular injection or an allergic reaction to the local anesthetic? What about emergency drugs for resuscitation?

Pre-medications are often used before we initiate the PNB to make the block more comfortable to the patient. While comfort of the patient is a high priority, patient safety is of utmost importance. Keeping the patient lightly sedated ensures that he can respond at all times during the PNB. He can, for example, communicate to you if he has a parasthesia while you perform the block, thereby decreasing the risk of an intraneural injection.

Know your anatomy.
Success of peripheral nerve blocks primarily depends on your understanding of the anatomy of the nerves in relation to their surrounding structures. A thorough understanding of the anatomy will save you time and the patient discomfort from multiple attempts. Here's a review of two blocking techniques.

  • Interscalene block. This upper-extremity block targets the brachial plexus at the level of the superior trunks. The brachial plexus is between the anterior scalene muscle and the middle scalene muscle. At the level of C6, posterolateral to the sternocleidomastoid, you should be able to palpate the interscalene (IS) groove. If it's difficult to discern the anterior and middle scalene muscles, ask the patient to take a deep breath and hold it. This maneuver separates the two scalene muscles, letting you palpate the IS groove. Another anatomical marker is the external jugular vein, which often crosses the IS groove at the level of C6. After palpating the IS groove, direct your needle slightly caudad, keeping the needle at a 60-degree angle to all planes.

When using a nerve-stimulator approach, contraction of different muscle groups will indicate where your needle is located relative to the IS groove and the brachial plexus. For example, stimulation of the diaphragm indicates you are anterior to the IS groove. Moving the needle posteriorly will bring you into the plane of the IS groove. Conversely, contraction of the rhomboids or the levator scapulae indicates that you are posterior to the IS groove. You'll need to move the needle more anteriorly.

  • Femoral nerve block (FNB). This block is primarily used for post-op pain relief after ACL repair or patellar tendon repair. The femoral nerve is the primary sensory nerve to the knee joint femur and patella. The nerve is divided into two divisions: anterior and posterior. The posterior division is the main trunk of the femoral nerve supplying motor to the quadriceps femoris and sensory to the knee joint, femur, and patella. Stimulation of the posterior division of the femoral nerve results in the "patellar snap." The best way to locate the patellar nerve is to identify the femoral artery pulse at the level of the inguinal crease.

Your starting point for attempting the FNB should be 1cm to 1.5cm lateral to the edge of the femoral pulse. If your first response is stimulation of the sartorius muscle, you have stimulated the anterior division of the femoral nerve. In 75 percent of patients, the posterior division of the femoral nerve lies either directly posterior or posterolateral of the anterior division. In 25 percent of patients, the posterior division lays posteromedial of the anterior femoral nerve. If you stimulate the sartorius, advance your needle directly posteriorly to try to stimulate the posterior division. If this doesn't illicit the patellar snap, move the needle more laterally, then medially, in an attempt to get the appropriate femoral-nerve response.

Use a nerve stimulator.
The most dependable way to obtain a solid peripheral nerve block is using the nerve stimulator. While the paresthesia method is known and a traditional method of performing peripheral nerve blockade, the nerve stimulator approach for most peripheral nerve blocks will provide for a more reliable block with a faster onset. Getting an evoked motor response between 0.2 and 0.4 milliampules (mA) with a grade II response at 0.4 mA is the goal.

Proper positioning.
Positioning the patient correctly will be one of your greatest assets in performing a successful PNB. By optimizing the patient's position, you'll be able to identify the anatomical landmarks more easily and optimize the nerve's position for anesthetization. Let's take, for example, an axillary block. You should place the patient in the supine position with the arm abducted 90 degrees and the forearm flexed 90 degrees. Hyperabduction of the arm will obscure the axillary artery pulse due to compression of the axillary artery between the first rib and the clavicle, by the tendon of the pectoralis major or from the head of the humerus.

In the transarterial approach, palpate the axillary artery pulse as proximally as possible with your index and second fingers. Using a 22g 1.5-inch B bevel needle, advance the needle slowly aiming for the arterial pulse, until bright red blood is continuously aspirated. Advance the needle, further transecting the artery, until no additional blood can be aspirated. Incrementally deposit the local anesthetic posterior to the artery, aspirating every 3cc to 4cc monitoring for intra-arterial injection. Once the block is completed, hold pressure with the arm adducted for five minutes to decrease the risk of hematoma and to encourage proximal flow of the local anesthetic in the axillary perivascular space.

Give yourself plenty of time.
One of the main reasons anesthesiologists shy away from regional anesthesia is due to the time that it takes for PNBs to set up. While onset may be as short as five minutes, it can take 20 minutes to 30 minutes for a surgical anesthesia depth. This time delay depends on the type of block and also the body habitus of the patient. It's not uncommon for an ankle block to require 20 minutes to 30 minutes to attain surgical anesthesia. In a muscular patient, onset of motor blockade in an ISB may be less than five minutes, however, C4 surgical anesthesia may require 20 minutes. Traditionally, axillary blocks also take 20 minutes to 30 minutes to obtain surgical anesthesia levels. Giving yourself adequate lead time to place the PNB ensures you the luxury of taking your time to ensure the optimal evoked motor response, thereby decreasing latency of the block and giving the block sufficient time to set up.

Being prepared
Peripheral nerve blocks can be very advantageous in today's OR setting. The key to being successful is good preparation and technique.