How do I perform an interscalene block?

Interscalene Block Technique for Shoulder Surgery

Interscalene brachial plexus block is the first-choice regional anesthetic technique for shoulder procedures including rotator cuff repair, providing superior analgesia compared to systemic medications alone. 1, 2

Patient Positioning and Preparation

• Position patient supine with head turned away from the side to be blocked
• Prepare the skin with antiseptic solution following standard aseptic technique
• Use ultrasound guidance to reduce the risk of complications 1

Anatomical Landmarks

• Identify the interscalene groove between the anterior and middle scalene muscles
• The C5-C7 nerve roots of the brachial plexus travel through this groove
• For ultrasound-guided technique, identify the following structures:
  • Anterior and middle scalene muscles
  • Brachial plexus nerve roots (appear as hypoechoic round structures)
  • Sternocleidomastoid muscle (superficial landmark)

Block Technique

1. Ultrasound-guided approach (preferred):

   • Use high-frequency linear transducer (10-15 MHz)
   • Place transducer at level of C6 (level of cricoid cartilage)
   • Identify nerve roots between scalene muscles
   • Use in-plane technique with needle directed from lateral to medial
   • Target the C5-C6 roots at the level of C7 to reduce phrenic nerve involvement 3
   • Observe local anesthetic spread around the nerve roots

2. Nerve stimulator technique (alternative):

   • Identify interscalene groove at level of C6
   • Insert needle at 45° angle to skin, directed medially and slightly caudally
   • Advance until motor response is elicited (shoulder/arm movement)
   • Target stimulation at 0.3-0.5 mA

Local Anesthetic Selection and Dosing

• Recommended dose: 5-10 mL of 0.75% ropivacaine 4
  • Lower volume (5 mL) provides similar analgesia with reduced phrenic nerve paralysis
  • Higher volume (10 mL) may provide longer duration but increases risk of hemidiaphragmatic paresis

Potential Complications and Management

1. Hemidiaphragmatic paresis:

   • Incidence: 33% with 5 mL vs 60% with 10 mL of local anesthetic 4
   • Use lower volumes and ultrasound guidance to reduce risk 3
   • Avoid in patients with respiratory compromise

2. Other complications:

   • Pneumothorax (0.2%)
   • Central nervous system toxicity (0.2%)
   • Horner's syndrome (18%)
   • Recurrent laryngeal nerve block (1%) 5

3. Prevention strategies:

   • Use ultrasound guidance
   • Perform at C7 level rather than higher cervical levels
   • Use minimum effective volume of local anesthetic
   • Avoid multiple needle passes

Multimodal Analgesia Protocol

For optimal pain management after rotator cuff repair:

1. Pre/intraoperative:

   • Paracetamol
   • COX-2 inhibitor
   • IV dexamethasone (prolongs block duration)
   • Interscalene block 1

2. Postoperative:

   • Continue paracetamol and NSAIDs/COX-2 inhibitors
   • Reserve opioids for rescue analgesia 1

Continuous vs Single-Shot Technique

• Continuous technique (catheter):

  • Recommended for major shoulder procedures with anticipated severe pain
  • Provides extended analgesia beyond 8-12 hours
  • More resource-intensive

• Single-shot technique:

  • Provides analgesia for approximately 8-12 hours
  • Simpler to perform
  • Requires robust multimodal analgesia for pain management after block resolution

Clinical Pearls

• Thoroughly test block success before proceeding with surgery to avoid emergency conversion to general anesthesia 1
• Consider combining with general anesthesia for shoulder surgery to reduce intraoperative opioid requirements 6
• For patients with respiratory compromise, consider suprascapular nerve block with/without axillary nerve block as an alternative 1, 2
• Use ultrasound guidance to improve accuracy and reduce complications 1

By following these recommendations, you can provide effective analgesia for shoulder procedures while minimizing complications associated with interscalene block.