How I Do It: External Oblique Intercostal Plane Block
Highlights
- The anterolateral upper abdominal wall receives innervation from the ventral rami of spinal nerves T6 - T10 (View Highlight)
- As these nerves course from their neuraxial origin to the midline, they give off two key branches – the lateral cutaneous and anterior cutaneous branches of the intercostal nerves (View Highlight)
- The external oblique is a thin, broad muscle that spans both the lower thorax and abdomen (Figure 1A). It originates on the external surfaces of ribs 5-12 where it also forms digitations with the serratus anterior and latissimus dorsi muscles. As it courses anteriorly from the midclavicular line, it forms an extensive aponeurosis, which eventually becomes part of the anterior rectus sheath. (View Highlight)
- Spinal nerves T6 – T9 emerge from the costal margin into the plane between the internal oblique and transversus abdominis (Figure 1B). They then enter the lateral border of the rectus sheath to eventually pierce the muscle and terminate as the anterior cutaneous branches (View Highlight)
- above the costal margin there is a deficiency in the posterior sheath, and the muscle epimysium lies directly on the costal cartilages with an intervening layer of fatty tissue, which provides a potential path for diffusion of local anaesthetic (View Highlight)
- The external oblique muscle can then be traced inferiorly to a subcostal view, and the probe rotated in a transverse orientation to find the traditional subcostal transversus abdominus muscle plane view (View Highlight)
- another means to confirm the appropriate location is to translate the probe laterally to visualize the junction between the serratus anterior and external oblique (View Highlight)
- Once the EOI plane is identified, rotation of the caudad portion of the probe laterally will result in a downhill needle trajectory. (View Highlight)