Ultrasound-Guided Serratus Anterior Blocks

Continuing Education Activity

Approximately 10 percent of injured patients presenting to the emergency department are found to have rib fractures. Rib fractures are associated with significant morbidity and mortality, especially in the elderly. Pulmonary complications, including pneumonia, often become apparent 2 to 3 days after the initial injury, when respiratory function becomes compromised secondary to pain. Therefore, effective analgesia is an important component of rib fracture management. Intravenous opioids are a mainstay of treatment but have side effects, including respiratory depression, depressed cough reflex, and delirium in the elderly. The ultrasound-guided serratus anterior plane block (SAPB) is a popular alternative due to its efficacy, relative ease, and limited side-effect profile. This activity reviews the technique for performing an ultrasound-guided serratus anterior plane block and its indications and contraindications. This activity highlights the role of the interprofessional team in managing analgesia.

Objectives:

• Describe the technique involved in performing an ultrasound-guided serratus anterior plane block.
• Review the indications for a serratus anterior plane block.
• Summarize the complications associated with serratus anterior plane blocks.
• Explain the importance of improving communication and care coordination among the interprofessional team to ensure the safe performance of the serratus anterior plane block and improve patient outcomes.

Introduction

Approximately 10% of injured patients presenting to the emergency department (ED) demonstrate rib fractures. Rib fractures are associated with significant morbidity and mortality, especially in the elderly.[1] Pulmonary complications, including pneumonia, often become apparent 2 or 3 days after injury, when respiratory function is compromised, secondary to pain. Therefore, effective analgesia is an important component of rib fracture management. Intravenous opioids are a mainstay of treatment but have side effects, including respiratory depression, depressed cough reflex, and delirium in the elderly.[1] The serratus anterior plane block (SAPB) is an alternative that has become popular due to its efficacy, relative ease, and limited side-effect profile.[2][3]

Anatomy and Physiology

The serratus anterior muscle originates from the anterior aspect of ribs 1 through 7-10 and inserts on the medial border of the scapula. It consists of 7 to 10 serrated tendinous projections that originate on each rib and is innervated by the long thoracic nerve.[4] Deep and superficial potential spaces bound the serratus anterior. At the level of the fifth rib, the superficial plane forms from the anterior aspect of the serratus anterior and the posterior aspect of the latissimus dorsi muscle. The deep plane forms from the posterior aspect of the serratus anterior and the external intercostal muscles and ribs.[5] Either plane will achieve analgesia to the anterolateral chest wall with reportedly similar efficacy and an equivalent area of cutaneous sensory loss.[5][6][7]

The SAPB targets the lateral cutaneous branches of the thoracic intercostal nerves, which arise from the anterior rami of the thoracic spinal nerves and run in a neurovascular bundle immediately inferior to each rib. At the midaxillary line, the lateral cutaneous branches of the thoracic intercostal nerve traverse through the internal intercostal, external intercostal, and serratus anterior muscles innervating the musculature of the lateral thorax.[8] These branches of the intercostal nerves, therefore, travel through the two potential spaces described above. Local anesthetic inserted into these planes will spread throughout the lateral chest wall, resulting in paresthesia of the T2 through T9 dermatomes of the anterolateral thorax.[5][8][6][5]

Indications

The SAPB has been used effectively for the management of pain in the context of rib fractures, rib contusions, thoracoscopic surgery, thoracotomy, breast surgery, and post-mastectomy pain syndrome.[3][2][5][2][3][9][7][10] In the setting of rib fractures, the block is effective in providing analgesia for lateral rib fractures but may be ineffective for anterior and posterior rib fractures.[8]

Contraindications

Absolute contraindications to the SAPB include allergy to local anesthetic medications or soft tissue infection in the area of the procedure. Relative contraindications include any anatomical variation that makes sonographic visualization of landmarks difficult. These include scarring and fibrosis due to prior thoracic surgery.

Equipment

A high-frequency (5 to 10 MHz or 6 to 13 MHz) linear transducer should be used to allow detailed visualization of superficial structures. Cardiac monitoring and an intravenous line are recommendations, and access to lipid emulsion therapy should be confirmed.

Personnel

The SAPB is performable by trained personnel who are familiar with the use of musculoskeletal and procedural sonography. 

Preparation

Informed consent should be obtained from the patient. The ultrasound machine should be situated opposite the operator, plugged in, and powered on. Sterile technique, including an ultrasound transducer cover and sterile gel, should be employed. The patient should be supine or in a lateral decubitus position. 

Technique or Treatment

A high-frequency linear transducer should be placed on the patient’s midaxillary line in the transverse plane, at the level of the fifth rib, with the indicator oriented toward the operator’s left. With the rib, pleural line, and overlying serratus anterior and latissimus dorsi muscles visualized, the skin can be anesthetized with a small volume of local anesthetic. Then, using ultrasound guidance, the needle is advanced in-plane at an angle of approximately 45 degrees towards the fifth rib. For the superficial SAPB, the local anesthetic is injected anteriorly to the serratus anterior.

For the deep SAPB, the local anesthetic is injected anteriorly to the rib and deep to the serratus anterior. The entirety of the needle should be visualized at all times throughout the procedure, and care should be taken to avoid any vessels while traversing the soft tissue. Once the needle tip is observed in the appropriate plane, a small aliquot of 1 to 3 mL of local anesthetic should be injected to confirm placement and to hydro-dissect the fascial layers and open the potential space. After opening the fascial plane, a larger volume of dilute local anesthetic, for example, 30 to 40 mL of 0.25% bupivacaine, should be gradually injected. The local anesthetic will appear as an enlarging anechoic stripe between fascial layers. Remove the needle and cover with sterile gauze or adhesive dressing. Reassess the patient’s pain level for improvement approximately five minutes after the block is complete.

Complications

Rebound pain is possible since the analgesia provided by bupivacaine typically lasts around six hours. Local anesthetic systemic toxicity (LAST) is a potential complication of regional anesthesia. For this reason, dilute anesthetic is used, and a maximum dose of 2 mg/kg of bupivacaine is the recommendation.[11] Pneumothorax is a potential complication but would entail catastrophic error since the fascial planes targeted in this block are superficial to the ribs, and the pleural line can be visualized clearly on ultrasound. If a pneumothorax is suspected, ultrasound can help to confirm lung sliding immediately after the procedure. Nerve injury is unlikely given the needle is not steered directly at nerves, but instead towards the plane through which the nerves run.

Clinical Significance

The ultrasound-guided SAPB offers an effective approach to the management of lateral chest wall pain, particularly in the context of traumatic rib fractures, and is a desirable alternative to opiate analgesia, especially in the elderly. 

Enhancing Healthcare Team Outcomes

Opioid abuse represents a public health crisis in the United States. Because almost half of ED patients complain of pain, and approximately 17% of patients discharged from EDs receive opioids, expanding options for effective analgesia in the acute setting can assist emergency physicians (EPs) in prescribing opiates responsibly.[12] The addition of regional anesthesia, such as the SAPB to the EP’s armamentarium, is particularly valuable in treating opioid-naïve patients since initiation of short-course opioid therapy seems to confer increased risk for further opioid use and addiction, with a number needed to harm of 48.[13][14] [Level 4] Nerve blocks such as the SAPB can be part of a multi-modal approach to the management of pain in the acute setting that offers to reduce reliance on opioids.

Review Questions

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References

1.

Lotfipour S, Kaku SK, Vaca FE, Patel C, Anderson CL, Ahmed SS, Menchine MD. Factors associated with complications in older adults with isolated blunt chest trauma. West J Emerg Med. 2009 May;10(2):79-84. [PMC free article: PMC2691509] [PubMed: 19561823]

2.

Khalil AE, Abdallah NM, Bashandy GM, Kaddah TA. Ultrasound-Guided Serratus Anterior Plane Block Versus Thoracic Epidural Analgesia for Thoracotomy Pain. J Cardiothorac Vasc Anesth. 2017 Feb;31(1):152-158. [PubMed: 27939192]

3.

Park MH, Kim JA, Ahn HJ, Yang MK, Son HJ, Seong BG. A randomised trial of serratus anterior plane block for analgesia after thoracoscopic surgery. Anaesthesia. 2018 Oct;73(10):1260-1264. [PubMed: 30120832]

4.

Smith R, Nyquist-Battie C, Clark M, Rains J. Anatomical characteristics of the upper serratus anterior: cadaver dissection. J Orthop Sports Phys Ther. 2003 Aug;33(8):449-54. [PubMed: 12968858]

5.

Blanco R, Parras T, McDonnell JG, Prats-Galino A. Serratus plane block: a novel ultrasound-guided thoracic wall nerve block. Anaesthesia. 2013 Nov;68(11):1107-13. [PubMed: 23923989]

6.

Biswas A, Castanov V, Li Z, Perlas A, Kruisselbrink R, Agur A, Chan V. Serratus Plane Block: A Cadaveric Study to Evaluate Optimal Injectate Spread. Reg Anesth Pain Med. 2018 Nov;43(8):854-858. [PubMed: 30063656]

7.

Piracha MM, Thorp SL, Puttanniah V, Gulati A. "A Tale of Two Planes": Deep Versus Superficial Serratus Plane Block for Postmastectomy Pain Syndrome. Reg Anesth Pain Med. 2017 Mar/Apr;42(2):259-262. [PubMed: 28079733]

8.

Mayes J, Davison E, Panahi P, Patten D, Eljelani F, Womack J, Varma M. An anatomical evaluation of the serratus anterior plane block. Anaesthesia. 2016 Sep;71(9):1064-9. [PubMed: 27440171]

9.

Durant E, Dixon B, Luftig J, Mantuani D, Herring A. Ultrasound-guided serratus plane block for ED rib fracture pain control. Am J Emerg Med. 2017 Jan;35(1):197.e3-197.e6. [PubMed: 27595172]

10.

Zocca JA, Chen GH, Puttanniah VG, Hung JC, Gulati A. Ultrasound-Guided Serratus Plane Block for Treatment of Postmastectomy Pain Syndromes in Breast Cancer Patients: A Case Series. Pain Pract. 2017 Jan;17(1):141-146. [PubMed: 27587333]

11.

El-Boghdadly K, Pawa A, Chin KJ. Local anesthetic systemic toxicity: current perspectives. Local Reg Anesth. 2018;11:35-44. [PMC free article: PMC6087022] [PubMed: 30122981]

12.

Strayer RJ, Motov SM, Nelson LS. Something for pain: Responsible opioid use in emergency medicine. Am J Emerg Med. 2017 Feb;35(2):337-341. [PubMed: 27802876]

13.

Hoppe JA, Kim H, Heard K. Association of emergency department opioid initiation with recurrent opioid use. Ann Emerg Med. 2015 May;65(5):493-499.e4. [PubMed: 25534654]

14.

Barnett ML, Olenksi AR, Jena AB. Opioid Prescribing by Emergency Physicians and Risk of Long-Term Use. N Engl J Med. 2017 May 11;376(19):1896. [PubMed: 28489999]

Disclosure: Samuel Southgate declares no relevant financial relationships with ineligible companies.

Disclosure: Meghan Herbst declares no relevant financial relationships with ineligible companies.