Background

Interscalene nerve block is the technique of delivering local anaesthetic in close proximity to the roots or trunks of the brachial plexus around the level of C6 vertebral body between the middle and anterior scalene muscles. The technique was well popularized and described by Alon Winnie in 1970. 

The procedure is mainly used for providing analgesia or surgical anaesthesia for the shoulder and upper arm. It is generally not appropriate for forearm or hand surgeries that require anaesthesia of the ulnar nerve distribution(C8-T1). Although shoulder surgery can sometimes be performed with just sedation and an interscalene block many practitioners prefer to combine it with general anesthesia for the best results. 

Indications

The procedure is indicated in the following: 

• Shoulder surgery: It offers analgesia and effective anaesthesia for a range of procedures, including rotator cuff repair, arthroscopy, acromioplasty, labral repair, and shoulder replacement. 
• Upper arm surgery: It is effective for surgeries involving the upper arm that require extensive regional anesthesia. 
• Pain management: Effective for acute postoperative pain management in the shoulder and upper arm region. 
• Certain trauma cases: Provides pain relief for trauma of shoulder and upper arm including fractures and dislocations. 
• Preoperative analgesia: This technique is frequently used alongside general anesthesia to improve pain control and minimize the need for intraoperative opioid use. 

Diagnostic procedures: It aids in diagnostic shoulder procedures by delivering substantial regional anaesthesia. 

Contraindications

The procedure is contraindicated in the following cases: 

1. Preexisting neurological issues 
2. Coagulopathy 
3. Patient refusal 
4. Severe COPD 
5. Allergy to local anesthesia 
6. Infection of planned site of injection 
7. Dysfunction of the contralateral phrenic nerve 

Outcomes

The procedure is typically carried out by anaesthesiologists, pain specialists and nurses. It requires specialized monitoring by physicians, resuscitation equipment, and an awareness of potential complications. When performed correctly, it can eliminate the need for general anaesthesia during arm surgery. 

Equipment

The following are required to perform a block: 

1. Sterile gloves 
2. Marking pen 
3. Peripheral nerve stimulator 
4. Skin or Antiseptic preparations like Chlorhexidine gluconate, alcohol or betadine 
5. Insulated, 22-gauge, short-beveled, two-inch stimulating needle 
6. Ultrasound machine 
7. Local anesthesia 
8. A block tray that contains ampoule of 1% lidocaine, 3-ml syringe, 25-gauge needle and sterile drape 

Patient preparation

For postoperative analgesia, peripheral nerve blocks are frequently carried out using 1.5% mepivacaine, 0.5% ropivacaine, and 0-25% to 0.5% bupivacaine. These treatments offer postoperative pain relief for 12 to 24 hours. The FDA authorized the use of injectable suspension of bupivacaine liposome in 2018 to generate post-surgical regional analgesia in adults after shoulder surgery by blocking the interscalene brachial plexus nerve. Phase 3 study data revealed statistically significant improvements with regard to initial opioid rescue over 48 hours, opioid-free patients and total postsurgical opioid intake. The suspension is meant to be used 48 to 72 hours after administration as a means of blocking nerves to treat pain related to shoulder surgery. In order to extend the duration of the block and provide an intravascular injection marker, epinephrine is frequently injected. One can choose a 1:600,000 blend that is more diluted. 

Patient positioning

The patient should be positioned supine with slightly elevated back and the head turned towards the nonoperative side. If using ultrasound guidance, placing a blanket behind the operative shoulder to elevate it off the bed can be helpful. 

Technique

1. Approach considerations 

Before performing an interscalene block, it is essential to palpate key anatomical landmarks, the interscalene groove, the sternocleidomastoid muscle, and the anterior scalene muscle. The sternocleidomastoid muscle is prominent and easily felt, while the anterior scalene muscle is located beneath it, extending toward the first rib. The interscalene groove which separates the middle and anterior scalene muscles, may be either subtle or distinct during palpation. It typically begins at the intersection of the sternocleidomastoid muscle and external jugular vein extending downward towards the midpoint of the clavicle. In patients with thicker and shorter necks, it is helpful to anticipate the groove’s location before palpating. 

To confirm correct identification of the groove, several techniques can be used. Deep inspiration can make the groove more pronounced as the scalenes are accessory muscles of respiration. The groove can be traced down towards the first rib to locate the subclavian artery which lies between the scalene muscles. However, the subclavian artery might not always be palpable due to its depth or because the omohyoid muscle covers the lower part of the groove. 

Technical considerations

Technique of nerve stimulation 

During this process, the patient will be fitted with monitoring equipment. The nerve stimulator will be adjusted along with administration of local anaesthetic. In addition to monitoring the patient, the assistant gives local anaesthetic and modifies the stimulator.  A block needle, a local anaesthetic and a sterilized block support tray are used to infiltrate the skin of the patient. Before inserting the needle, the nerve stimulator is adjusted to 1.0-1.5mA. Muscle contractions result from the needle being inserted slightly caudally and perpendicular to planes. By reducing the current gradually to 05mA or below, the threshold current is found. The needle is moved if the threshold is greater. Injections are made gently aspirating every three to five millilitres. The positioning of the needle during the interscalene block can affect unintentional motor responses. 

Technique with the guidance of Ultrasound

Interscalene block using ultrasound 

Once the patient is correctly positioned, disinfect the skin and place the transducer on the neck to identify the relevant structures and landmarks. There are two commonly used techniques for obtaining the proper image: 

Cricoid cartilage method: The transducer should be placed at cricoid cartilage level which is found medially to the sternocleidomastoid muscle and locate the carotid artery. Move the probe sideways till the brachial plexus is found in between the anterior and middle scalene muscles. 

Supraclavicular method: To locate the brachial plexus and subclavian artery, put the transducer just above the clavicle. The transducer should be moved upwards the neck of the patient while ensuring that the brachial plexus remains visible until the “stop-light” image is achieved. 

The needle needs to be placed in a plane parallel to the transducer entering from the side and going towards the centre. An alternative method would have the needle inserted the other way around. When the needle comes across the groove between two scalene muscles, create a vacuum carefully and then inject local anaesthetic. Patients should have their arms and shoulders moving when a nerve stimulator is being used. 

Performing procedure without ultrasound 

First, identify the important landmarks and mark them with the help of a marker pen before cleaning the skin. The three main landmarks for this procedure are the external jugular vein, clavicle, and the sternocleidomastoid clavicular head. Cricoid cartilage may also be useful as a landmark. Having marked the landmarks, prepare the skin and, with sterile gloves, palpate the middle and anterior scalene muscles. The sternocleidomastoid clavicular head can be found just behind these muscles at the cricoid cartilage. The external jugular vein usually passes over the top of interscalene furrow. 

Anesthetize the skin using 3 mL of local anaesthetic administered subcutaneously. Place the needle just behind the external jugular vein, about 3cm to 4 cm on the top of the clavicle and angle it perpendicular to the skin. After attaching the nerve stimulator, advance the needle until brachial plexus stimulation is achieved. This usually happens at a depth of 1cm to 2cm in many patients. Administer local anaesthesia while performing intermittent aspirations to prevent intravascular injection. 

Complications

1. Hematoma or bleeding 
2. Total spinal anesthesia 
3. Pneumothorax 
4. Permanent injury to nerve 
5. Paralysis of one side of the diaphragm 
6. Subarachnoid or epidural injection 
7. Toxicity due to local anesthesia 
8. Infection 
9. Puncture of vasculature 
10. Horner syndrome 

References

Interscalene Block – StatPearls – NCBI Bookshelf (nih.gov) 

References

Interscalene Block – StatPearls – NCBI Bookshelf (nih.gov)