Interscalene block

Interscalene block

Anesthesia type	Regional
Airway	None
Lines and access	PIV
Monitors	EKG, BP, Pulse oximetry
Primary anesthetic considerations
Preoperative
Intraoperative	Nerve injury
Postoperative	Local anesthetic systemic toxicity
Article quality
Editor rating	Unrated
User likes	0

An interscalene brachial plexus block is a form of moderate-term anesthesia and analgesia used for surgical procedures of the shoulder, proximal humerus, and/or lateral forearm. The technique consists of injecting local anesthetic around the cervical roots of the brachial plexus. Utilizing a posteriolateral approach provides extremity analgesia without the need for general anesthesia and a reduced risk of intravenous injection.

Overview

The interscalene brachial plexus block has been performed with varying success throughout the 20^th century, before being formally attributed in 1970 to Alon Winnie, who reported a percutaneous approach to the brachial plexus block with >90% effectiveness. While peripheral nerve stimulators are used to aid with identification and isolation of C5-C7 nerve roots, the introduction and development of ultrasound imaging has resulted in ultrasound-guided regional anesthesia.

Indications

An interscalene brachial plexus block should be considered for surgical procedures of the shoulder and/or lateral extremity. The interscalene block can provide between 8-14 hours of anesthesia and analgesia, depending on the anesthetic and adjunctive medications used. Common surgical procedures include, but are not limited to, shoulder arthroscopy, shoulder debridement, rotator cuff repair, SLAP (superior labral anterior-posterior) lesions/tears, shoulder replacement, humeral fracture repair, and/or radial fracture repair.

The decision to perform an interscalene block requires collaborative discussion between the surgeon and regional anesthesia provider. There may be temporal or anatomical limitations to performing this block due to patient acuity. Surgeon’s preference regarding regional anesthesia may also factor into decision-making. Some procedures, such as shoulder arthroscopy, produces mild or moderate post-operative pain that can be mitigated by other management techniques.

Contraindications

Absolute contraindications:

• Patient refusal
• Open wounds, sores, trauma, bleeding, or active soft tissue infections of the neck or extremity of interest
• Hypersensitivity/allergy to local anesthetics

Relative contraindications:

• Uncooperative patient

• COPD
• Contralateral paresis of phrenic or recurrent laryngeal nerves
• Previous neurologic deficit of the involved arm
• Anticoagulation
  • The overall incidence of bleeding complications following peripheral nerve blocks, in the anti-coagulated patient, is estimated at 0.82%. Current ASRA guidelines recommend utilizing neuraxial guidelines and precautions in the setting of peripheral nerve blocks.

Procedure Technique

The patient can be positioned in a supine, semi-supine, or semi-lateral decubitus position with their head rotated away from the upper extremity side being blocked. The semi-supine position is preferred as it allows the patient’s head to be slightly elevated, allowing for improved visualization and easy identification of the sternocleidomastoid (SCM) muscle. Once superficial landmarks are appropriately identified, the patient should be cleaned and draped in the sterile fashion. Utilizing a linear ultrasound probe, the carotid artery, anterior & middle scalene muscle, SCM muscle, and brachial plexus should be identified along the C6 transverse plane. The desired view of C5-C7 nerve roots is often identified as the “stoplight” or “snowman” sign with fine-tune adjustments of the probe. Using a posteriolateral, in-plane approach, 2% lidocaine, or alternative, should be administered to the superficial area. Utilizing the same injection site, the block needle is inserted in-plane, towards the brachial plexus, along the same posteriolateral approach. Direct visualization of the needle and needle tip should be maintained throughout the procedure. Once the needle tip is approximated near the C5-C7 nerve roots, the provider aspirates to ensure the needle tip is not located within a blood vessel. Once aspiration-negative, the provider can inject 3-5ml of local anesthetic to ensure proper placement of the needle, appropriate hydro-dissection, and local anesthetic spread. The provider can then inject, redirect, and inject further local anesthetic, taking care to aspirate after every 3-5ml of injected local anesthetic or immediately following needle repositioning. The overall effectiveness of an interscalene block varies upon where local anesthetic is located. Two common areas of injection are between the middle scalene muscle and brachial plexus sheath (peri-plexus) versus an injection within the brachial plexus sheath (intra-plexus). While there is no difference between the block onset and block quality with either approach, intra-plexus blocks have been shown to last 2-3 hours longer than peri-plexus blocks.

Procedural sedation can be considered for patients undergoing interscalene blocks. Commonly used medications include Midazolam (0.5-4 mg IV as needed) and Fentanyl (25-100 mcg IV as needed).

Choice of Local Anesthetic

The choice of local anesthetics (LA) is determined by the goal of the block (operative analgesia) and desired block duration. 0.5% Bupivacaine is one of the most common choices for interscalene blocks, but availability of this medication for regional anesthesia may vary.

Choice of local anesthetic — Choices of LA for interscalene block varies, but include:

·       Pre-operative anesthesia: 2% lidocaine, 0.5% bupivacaine, or 1.5% mepivacaine.

·       Post-operative analgesia: 0.25-0.5% bupivacaine or 0.5% ropivacaine.

2-5ml of 2% lidocaine, for the standard 70kg patient, is a common choice for superficial local anesthesia/analgesia prior to performing the interscalene block.

For a 70kg patient, the minimum effective volume of 0.5% bupivacaine (with adjunct epinephrine (1:200,000)) was reported to be 0.95ml, with adequate postoperative analgesia obtained with approximately 2.34ml. However, provider experience, preference, patient’s anatomy, adjunct medication(s), and overall successful spread of local anesthesia should be considered. It is therefore reasonable to prepare and inject between 10-25ml of local anesthesia, monitoring for effective volume spread and the toxic dose limit of the local anesthetic.

Adjunct Medications

Many agents have been studied as adjunct medications administered in regional blocks. The intent of adjunct medications is to increase the duration of analgesia of the nerve block without prolonging motor blockade. Various medications have been studied, including clonidine, dexmedetomidine, and dexamethasone, providing between 2- 8 hours of additional analgesia. Epinephrine is reported to increase the mean duration of a nerve block by 1 hour, likely due to decreased systemic uptake of the anesthetic agent, rather than direct sensory and/or motor blockade.

Potential Complications

Major Adverse Events

Local anesthetic systemic toxicity (LAST) is one of the greatest risks associated with any form of regional nerve blocks due to intravenous anesthetic injection. Possible intravenous anesthetic injection sites include the nearby carotid or vertebral artery. LAST can presents with various signs and symptoms, but is commonly associated with perioral paresthesias, audio-visual disturbances, sudden change in mental status, or seizures. While LAST is extremely uncommon, regional anesthesia providers and teams should be observant for any signs of LAST during and following the procedure. Intravenous lipid emulsion therapy should be readily available where regional blocks are being performed to rapidly manage LAST.

Minor Adverse Events

Horner’s Syndrome (Stellate Ganglion block) is another well-known side-effect of the interscalene block of the brachial plexus and occasionally, epidural analgesia. While this presentation is often transient, cases of long-lasting Horner’s syndrome have been reported. Laryngeal nerve block and/or phrenic nerve block sequala have also been reported despite the use of ultrasound imaging. Given an increased risk of incidental or secondary phrenic nerve block, interscalene nerve blocks should be avoided in patients with documented pulmonary compromise if unable to tolerate up to a 30% decreased in vital capacity or forced expiratory volume over 1 second (FEV₁).

Additional adverse events include accidental vascular puncture or neuraxial injections.