Serratus anterior plane block: Anatomical landmark-guided technique

Sir,

Following the pioneer description of ultrasound guided serratus anterior plane block (SAPB) by Blanco et al.,[1] it has been used effectively to provide analgesia for various indications.[2] It was also described using a peripheral nerve stimulator (PNS) by stimulating long thoracic nerve above the serratus anterior muscle.[3] We describe a novel anatomical landmark-guided technique of SAPB for acute as well as chronic pain management.

In landmark-guided SAPB, our aim is to deposit the local anesthetic (LA) in the fascial plane deep to serratus anterior muscle (SAM) and above the ribs or external intercostal muscle [Figure 1a]. It is performed in lateral decubitus position with the nondependent arm flexed, abducted and raised over head, or in supine position with the ipsilateral arm abducted. The supine position with a folded sheet or a thin pillow placed under the back on the side to be blocked is more comfortable for the patient and allows easy identification of landmarks. The fifth rib is identified and traced till the midaxillary line. This intersecting point is the needle insertion point [Figure 1b]. Deep SAPB blocks the lateral cutaneous branches of intercostal nerves (T2--T6, depending on the level of injection and the volume of LA injected) before their division into anterior and posterior terminal branches.[4] LA injection in this plane is unaffected by surgical dissection, does not diffuse to superficial plane, and thus blockade of long thoracic nerve and thoracodorsal nerve are also avoided.

Figure 1.

(a) Schematic diagram of SAPB. (b) Needle insertion point. (c) Back Flow of LA. (d) Ultrasound confirmation. LDM = Latissimus Dorsi Muscle, SAM = Serratus Anterior Muscle, ICM = Intercostal Muscles, LA = Local Anaesthetic, MAL = mid axillary line

Under aseptic precautions, the needle (22-gauge, 2.5–5 cm short bevelled needle or blunt tipped hypodermic needle) is inserted and advanced perpendicular to the skin in all planes to contact the rib [Figure 1a]. The depth of rib from the skin varies depending upon the build of the individual. After hitting the rib, the needle tip is withdrawn 1--2 mm. At this point, the needle tip lies between the SAM and the rib. After negative aspiration for blood or air, LA is injected in 3–5 ml aliquots. A volume of 20–25 ml of 0.25% (levo) bupivacaine or 0.2% ropivacaine with or without adjuvants can be used for analgesia depending upon the surgery and requirements.

Case 1

A 42-year-old lady was admitted with a lump in the right breast. She had undergone modified radical mastectomy under general anesthesia and SAPB. This patient demonstrated analgesia involving T2–T6 dermatomes lasting 24 h with a single injection of 25 mL 0.25% bupivacaine with 8 mg dexamethasone and multimodal analgesia.

Case 2

A 60-year-old lady who had undergone left modified radical mastectomy 2 years back, presented with pain along the site of incision and inner side of left arm. Following landmark-guided SAPB her numeric rating scale score came down to 0 from 7 on a scale of 10. Other analgesics requirement was also decreased.

If the drug is deposited in correct plane, LA will be dripping from needle hub upon disconnection of the syringe [Figure 1c]. Absence of backflow may indicate intramuscular injection. The drug injected in deep serratus plane spreads in both cephalocaudal and anteroposterior directions over several levels depending on the volume of LA administered [Figure 1d]. Although it is simple and easy to perform, a randomized controlled trial is required to validate its efficacy, safety, and reliability compared with PNS or ultrasound-guided techniques.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.