Lecture Notes: PEX 2 Block and Soner Anatomy

Introduction

• Purpose of the Lecture: Demonstrate how to scan for and perform a PEX 2 block.
• Indications: Useful for breast surgery or any surgery involving the chest wall.
• Analgesia Coverage: Provides analgesia between T1 and T5.

Procedure Overview

• Anesthetic Dosage: 30 mL of 0.25% Bupivacaine, divided into two injections:
  • 10 mL between Pectoralis Major and Minor
  • 20 mL between Pectoralis Minor and Serratus Anterior
• Bilateral Block Caution: Avoid exceeding toxic dosage.

Neural Innervation of Anterior Chest Wall and Breast

• Supraclavicular Nerve: Innervates superior chest wall.
• Medial and Lateral Pectoral Nerves: Provide sensory, motor, and sympathetic innervation to pectoral muscles.
• Thoracodorsal Nerve: Innervates Latissimus Dorsi.
• Long Thoracic Nerve: Innervates Serratus Anterior.
• Intercostal Cutaneous Nerves: Branches from T2 to T6.

Relevant Anatomy for PEX Block

• Structural Layers:
  • Skin and subcutaneous tissue
  • Clavicle
  • Pectoralis Major
  • Pectoralis Minor
  • Serratus Anterior
• Vascular and Nerve Components:
  • Thoracoacromial artery
  • Lateral Pectoral Nerve
  • Medial Pectoral Nerve

Ultrasound Scanning Technique

• Initial Probe Position: Paramedian orientation contacting the clavicle.
• Key Visualization Points:
  • Clavicle
  • Pectoralis Major and Minor
  • Subclavius
  • Axillary artery and vein
  • Ribs (Second rib likely visible with pleura adjacent)
• Probe Movement:
  • Slide down the chest to count ribs
  • Rotate 90° at the third rib

Performing the PEX Block

• Needle Insertion:
  • Insert anteriorly and directed laterally.
  • Identify fascial plane between Pectoralis Major and Minor.
  • Inject 10 mL of anesthetic.
  • Advance needle to fascial plane between Pectoralis Minor and Serratus Anterior.
  • Inject 20 mL of anesthetic.

Tips for Success

• Ergonomics: Optimize positioning and line of sight with ultrasound.
• Needling Technique: In-plane needling recommended for better needle visualization.
• Structure Identification: Always identify pectoral branches, pleura, and needle tip.
• Safety Measures: Use ribs as stop-gap to prevent deep needle traversal towards pleura.
• Dosage Adjustment for Bilateral Blocks: Dilute anesthetic for patients <70kg to avoid toxicity.