Procedure: Serratus Anterior Block

Procedure, instrructions and discussion

Serratus Anterior Plane Block

Today we’re exploring a technique for rib fracture pain: the Serratus Anterior Plane (SAP) block. As always, we’ve reviewed the latest evidence and translated it into practical bedside tips.

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The rationale…

Indications

• Anterolateral rib fractures (T2-T9 dermatomes)

AND

• Ongoing opioid analgesic requirements

THE SERRATUS ANTERIOR BLOCK MAY OFFER SOME PAIN RELIEF FOR POSTERIOR RIB FRACTURES

IT CAN BE CONSIDERED IF AN ALTERNATIVE TECHNIQUE SUCH AS THE ERECTOR SPINAE BLOCK IS UNAVAILABLE

Contraindications (absolute in bold)

• ALLERGY TO LOCAL ANAESTHETIC
• LOCAL INFECTION
• Severe liver failure (risk of local anaesthetic toxicity)
• Heart block without pacemaker (risk of local anaesthetic toxicity)
• Distorted local anatomy / inability to identify sonographic landmarks

Alternatives

• Oral pain relief
• IV opioids (consider PCA)
• Other regional anaesthesia techniques (erector spinae block, thoracic epidural, paravertebral block etc)

Consent

VERBAL – IF HAS CAPACITY

• Simple procedure with a low risk of complications

NOT REQUIRED – IF LACKS CAPACITY

• Emergency procedure to prevent pain and distress
• Brief verbal explanation of the procedure is still recommended for the patient who lacks capacity.

Example: ‘I’m going to give you and anaesthetic injection to help with your pain. We do this regularly and it will make you more comfortable”.

Potential complications

• Allergy
• Failure (ineffective pain relief)
• Damage to adjacent structures (nerve, artery, pleura)
• Infection
• Bleeding
• Local anaesthetic toxicity

Infection control

• Standard precautions
• Aseptic non-touch technique
• PPE: Sterile gloves, sterile drape, sterile US cover and gel

Area

• Monitored bed (with access to rescue equipment and medications)

Staff

• Procedural clinician
• Assistant

Equipment

• Ultrasound
• High frequency linear probe (nerve preset)
• Dressing pack
• 22g 50 mm needle (nerve block needle is ideal)
• Luer lock syringe (50-60ml or 20ml x 2)
• Drawing up needle
• 2x 10mL Normal Saline vials
• Minimal volume extension tubing
• Small dressing
• Marking pen

Positioning (patient)

• Lying on side position with injured side up and back towards operator

or

• Supine position with arm abducted and externally rotated (hand behind head)

Positioning (probe)

• Linear probe over Latissimus dorsi muscle
• Transverse orientation at posterior axillary line at level of the nipple (T4)
• Probe marker pointing towards operator if patient on side or upwards if supine

Medication

• Lignocaine 1% 5ml for skin anaesthesia, then
• Ropivacaine 0.375% 40ml (3mg/kg maximum), or
• Bupivacaine 0.25% 40ml (2mg/kg maximum)

ROPIVACAINE IS OFTEN SUPPLIED AS 0.75% SOLUTIONS

DILUTE 20 ML OF 0.75% ROPIVACAINE WITH 20 ML OF SALINE

Sequence (Serratus anterior block)

• Identify with ultrasound the Latissimus dorsi muscle and Serratus anterior muscle (SAM)
• Identify the superficial serratus plane between these muscles often identified by thoracodorsal artery (TDA)
• Infiltrate Lignocaine into skin and subdermal layers 0.5 cm in front of probe foot plate (needle entry point)
• Insert block needle in-plane, perpendicular to skin
• Holding shaft of needle 0.5cm from tip, applying constant pressure until tip pierces through skin
• Slide probe towards needle to identify needle tip and shaft
• Advance the needle tip towards the superficial serratus plane without losing sight of the needle tip.
• Pierce through the superficial layer of the SAM adjacent to the TDA (you will feel a ‘pop’)
• Aspirate to confirm the needle is not in a blood vessel then inject 2-4ml of Ropivocaine
• Observe Latissimus dorsi muscle separating SAM with anechoic fluid
• If resistance is felt then the needle tip is within the muscle, withdraw the needle 1-2 mm and re-attempt
• Inject the remainder of the local solution slowly over 1 -2 minutes, aspirating every 5ml
• Withdraw the needle and apply dressing with gentle pressure

Sequence (tissue planes unclear)

• Introduced needle under direct ultrasound guidance until it reaches the body of the rib
• Once in contact with the rib instil the local anaesthetic
• Observe for hydro-dissection above the rib

Post procedure care

MONITORING

• Carry out continuous cardiac monitoring for 15 minutes post procedure (local anaesthestic toxicity)
• Monitor hourly for two hours, then every four hours (general observation chart and pain assessment)

ONGOING CARE

• Provide and chart oral pain relief, PCA, anti-emetics
• Document verbal consent, local anaesthetic given, procedure and immediate complications

Tips

• Ropivacaine is the preferred local anaesthetic agent due to prolonged action and reduced cardiac toxicity
• Ropivacaine usually comes in a 0.75% solution and requires dilution 1:1 with saline to 0.375%
• If resistance to injecting is felt, withdraw needle slightly as it may be in muscle below fascia
• Inserting the needle perpendicular to the skin allows easier insertion
• Inserting the needle in front of the probe then sliding the probe back ensures site of the needle tip

Discussion

The serratus anterior plane (SAP) blocks is an ultrasound-guided regional anaesthesia technique that provides analgesia to most of the ipsilateral hemithorax. In the setting of rib fractures, it can provide rapid and significant pain relief, increasing the proportion of patients who have a meaningful early reduction in their pain score to levels that are less than moderate in severity.

These benefits are seen most reliably when the block is added to established, multidisciplinary ‘chest injury pathways’. Some studies report reduced opioid use, though findings vary. Respiratory function consistently improves, with increases in inspiratory volume, incentive spirometry, and oxygenation, and decreases in respiratory rate. When performed under ultrasound guidance, SAP blocks have not been associated with major complications.

The Serratus Anterior Plane (SAP) block is performed by depositing local anaesthetic in one of two fascial planes: either superficial to the serratus anterior muscle, between it and the latissimus dorsi, or deep to it, between the serratus anterior and the ribs (or external intercostal muscles).

We recommend the superficial approach where tissue planes are visible to minimise the risk of pneumothorax. Both approaches aim to anesthetize the lateral cutaneous branches of the thoracic intercostal nerves, typically from T2 to T9. The superficial approach tends to be technically easier and may result in broader spread of anaesthetic, while the deep approach lies closer to the target nerves and may offer more focused and potentially longer-lasting analgesia. The deep approach remains a safe option in the setting of local tissue distortion (e.g. subcutaneous emphysema or haematoma).

One of the serious but rare complications of regional anaesthesia is local anaesthetic systemic toxicity (LAST), which can result from inadvertent intravascular injection. While the estimated incidence is low (20 per 100,000 procedures) the consequences can be life-threatening. This risk can be significantly reduced through adherence to good injection technique and the use of ultrasound guidance, which improves visualization of vascular structures and helps avoid unintentional intravascular administration.

Early signs of local anaesthetic toxicity may include circumoral tingling, light-headedness, visual disturbances, seizures, or cardiac arrhythmias. If any of these symptoms occur during administration, the injection should be stopped immediately and assistance sought. In the event of progression to cardiac arrest, standard cardiopulmonary resuscitation (CPR) should be initiated promptly, alongside lipid rescue therapy using 20% intralipid.

In practice, lipid rescue for a 70 kg adult involves taking a 500 mL bag of 20% intralipid and administering two immediate 50 mL IV boluses using a 50 mL syringe. The remainder of the bag should then be infused via an IV administration set at a rate of 1050 mL/hour. If there is no return of spontaneous circulation, up to two additional bolus doses may be given.

It is also important to consider individual risk factors and be cautious in patients with severe hepatic failure (which may delay amide local anaesthetic metabolism) and heart block without a pacemaker.

Adding dexamethasone to local anesthetic can increase the duration of the block. This can be added to Bupivacaine for those familiar with this technique. Dexamethasone cannot be added to Ropivacaine due to crystallization risk.

References

• Abu-Elwafa W, Ragab I, Abdelrahman A, Mahmoud W. Comparative Study Between Efficacy of Serratus Anterior Muscle Block as A Regional Analgesia Technique and I.V Morphine Infusion in Patient with Fracture Ribs 2021.
• Buttner R, Cherian N. Serratus Anterior Plane Block. LITFL
• Beard L, Hillermann C, Beard E, Millerchip S, Sachdeva R, Gao Smith F, Veenith T. Multicenter longitudinal cross-sectional study comparing effectiveness of serratus anterior plane, paravertebral and thoracic epidural for the analgesia of multiple rib fractures. Reg Anesth Pain Med. 2020 May;45(5):351-356.
• Bhalla PI, Solomon S, Zhang R, Witt CE, Dagal A, Joffe AM. Comparison of serratus anterior plane block with epidural and paravertebral block in critically ill trauma patients with multiple rib fractures. Trauma Surg Acute Care Open. 2021 Jan 8;6(1):e000621.
• Diwan S, Nair A. A retrospective study comparing analgesic efficacy of ultrasound-guided serratus anterior plane block versus intravenous fentanyl infusion in patients with multiple rib fractures. J Anaesthesiol Clin Pharmacol. 2021 Jul-Sep;37(3):411-415.
• El Malla DA, Helal RAEF, Zidan TAM, El Mourad MB. The Effect of Erector Spinae Block versus Serratus Plane Block on Pain Scores and Diaphragmatic Excursion in Multiple Rib Fractures. A Prospective Randomized Trial. Pain Med. 2022 Mar 2;23(3):448-455
• Gorecha M, Menon A, Woodford E, Yahia S, Marimuthu K. Early Serratus Plane Block for Rib Fracture Management could Avoid Intensive Care Unit Admission. Indian J Crit Care Med. 2020 Oct;24(10):995.
• Harrington C, Bliss J, Lam L, Partyka C. Serratus Anterior Plane Block for Clinically Suspected Rib Fractures in Prehospital and Retrieval Medicine. Prehosp Emerg Care. 2024;28(1):30-35
• Hernandez N, de Haan J, Clendeninn D, Meyer DE, Ghebremichael S, Artime C, Williams G, Eltzschig H, Sen S. Impact of serratus plane block on pain scores and incentive spirometry volumes after chest trauma. Local Reg Anesth. 2019 Aug 2;12:59-66
• Partyka C, Asha S, Berry M, Ferguson I, Burns B, Tsacalos K, Gaetani D, Oliver M, Luscombe G, Delaney A, Curtis K. Serratus Anterior Plane Blocks for Early Rib Fracture Pain Management: The SABRE Randomized Clinical Trial. JAMA Surg. 2024 Jul 1;159(7):810-817.
• Partyka C, Miller M, Burgess S, Drury K, Delaney A, Curtis K. Anatomical Location of Rib Fractures and Associated Analgesic Benefits Achieved From Serratus Anterior Plane Blocks: A Spatial Point Pattern Analysis. Anesth Analg. 2025 Jan 1;140(1):231-234
• Katou R, Mano T, Masuda T. Serratus anterior fascia plane block for pain control in patients with multiple rib fractures. J Phys Ther Sci. 2023 Sep;35(9):673-677. doi: 10.1589/jpts.35.673
• Kring RM, Mackenzie DC, Wilson CN, Rappold JF, Strout TD, Croft PE. Ultrasound-Guided Serratus Anterior Plane Block (SAPB) Improves Pain Control in Patients With Rib Fractures. J Ultrasound Med. 2022 Nov;41(11):2695-2701
• Lentz B, Kharasch S, Goldsmith AJ, Brown J, Duggan NM, Nagdev A. Diaphragmatic Excursion as a Novel Objective Measure of Serratus Anterior Plane Block Efficacy: A Case Series. Clin Pract Cases Emerg Med. 2022 Nov;6(4):276-279
• Lundén AR, Tarkkila P. An ultrasound-guided serratus anterior plane block with continuous local anaesthetic infusion and epidural analgesia for rib fracture pain. Acta Anaesthesiol Scand. 2024 Mar;68(3):394-401
• Martinez T, Belveyre T, Lopez A, Dunyach C, Bouzit Z, Dubreuil G, Zetlaoui P, Duranteau J. Serratus Plane Block Is Effective for Pain Control in Patients With Blunt Chest Trauma: A Case Series. Pain Pract. 2020 Feb;20(2):197-203
• Mukherjee K, Kasotakis G, Agarwal S Jr. It takes a village and a multimodal toolbox: pain control after multiple rib fractures. Trauma Surg Acute Care Open. 2024 Jun 13;9(1):e001478
• Mostafa MF, Bakr MA, Seddik MI, Mahmoud MMM, Ibrahim GMA, Ahmed AT. Ultrasound-guided deep versus superficial continuous serratus anterior plane block for pain management in patients with multiple rib fractures: A prospective randomized double-blind clinical trial. Saudi J Anaesth. 2025 Jan-Mar;19(1):58-64.
• Paul S, Bhoi SK, Sinha TP, Kumar G. Ultrasound-Guided Serratus Anterior Plane Block for Rib Fracture-Associated Pain Management in Emergency Department. J Emerg Trauma Shock. 2020 Jul-Sep;13(3):208-212.
• Sadauskas V, Fofana M, Brunson D, Choi J, Spain D, Quinn JV, Duanmu Y. Serratus anterior plane block improves pain and incentive spirometry volumes in trauma patients with multiple rib fractures: a prospective cohort study. Trauma Surg Acute Care Open. 2024 Jun 13;9(1):e001183

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