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Serratus Anterior Nerve Block

Welcome to the Serratus Anterior Nerve Block regional anesthesia page. Here we will cover indications, contraindications, materials and steps for you to master this procedure. Let’s begin with the overview below.

Overview

The serratus plane block can be used to provide analgesia to the chest wall. The idea is to inject a large volume of diluted anesthetic into the plane directly above the serratus anterior muscle, which is where the lateral cutaneous branches of the thoracic intercostal nerves run.[1] The anesthetic should spread throughout the plane, providing analgesia to the chest wall of the affected side.[2] Done correctly, this nerve block can be an excellent adjunct for pain control in rib fractures, as the pain is oftentimes difficult to control with oral or IV medications.[3]

Indications

For pain control in lateral and anterior rib fractures or chest tube placement.

Contraindications

There are few true contraindications to this block. They include:

  1. Infection (cellulitis) at the site of injection
  2. Allergy to local anesthetic being used
  3. Patient refusal

Anatomy

Some relative contraindications to consider are:

The latissimus dorsi lies superficial to the serratus anterior and is recognized as a triangular structure on ultrasound. The serratus anterior turn lies superficial to the ribs, intercostal muscles and pleura. (Image 1)

Materials

Technique

  1. Have the patient lying supine or even in slight lateral decubitus position. (Image 2)
  2. Place the linear probe in the mid-axillary line, in a transverse position. Visualize the triangle shaped latissimus dorsi muscle, the serratus anterior muscle, the ribs, and the pleura. (Image 1)
  3. Once you have found your spot, clean the skin and make a skin wheel with the lidocaine.
  4. Switch to the block needle with your 30 mL mixture of local anesthetic and sterile saline. Under ultrasound guidance, enter through the skin wheel you have created. Your needle will enter from a lateral position, in-plane with the ultrasound probe. (Images 3 and 4)
  5. Visualize your needle tip the entire time! It is helpful to use the rib as a backdrop to minimize chance of puncturing the pleura.
  6. Once your needle tip is directly deep to the latissimus dorsi and superficial to the serratus anterior muscle, aspirate to confirm you are not intravascular and then inject a small amount of dilute anesthetic. (~2-4cc).
  7. If you are in the correct plane, the facia will “unzip” as the fluid spreads throughout the plane. 
  8. If you are in the serratus anterior muscle, your injection will have the appearance of an intramuscular injection. If you are intramuscular, slowly withdraw needle until it appears to be directly above serratus anterior muscle, and again aspirate then inject a small amount of anesthetic.
  9. Do this until you see the “unzipping” effect, indicating that you are in the fascial plane and not in the muscle.
  10. Once confirmed you are in the facial plane, inject the rest of the dilute anesthetic, visualizing needle tip throughout.

Summary & Bullet Points

  1. This is an excellent nerve block for lateral or anterior rib fractures
  2. Use a linear probe
  3. Find the latissimus dorsi muscle and the serratus anterior muscle
  4. Use a rib as a back-drop to minimize risk of pneumothorax
  5. Inject anesthetic into the plane above the serratus muscle
  6. Re-evaluate the patient in 20-30 minutes to monitor for improvement in pain

References

[1] Pectoralis and Serratus Plane Nerve Blocks. NYSORA, Inc. Retrieved April 20, 2023, from https://www.nysora.com/topics/regional-anesthesia-for-specific-surgical-procedures/thorax/pectoralis-serratus-plane-blocks/

[2] Serratus Anterior Plane Block. Life in the Fastlane. Retrieved April 20, 2023, from https://litfl.com/serratus-anterior-plane-block/#:~:text=The%20Superficial%20Serratus%20Anterior%20Plane,with%20acute%20anterolateral%20rib%20fractures.

[3] Southgate SJ, Herbst MK. Ultrasound Guided Serratus Anterior Blocks. [Updated 2022 Jul 25]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan. Available from: https://www.ncbi.nlm.nih.gov/books/NBK538476/

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