The External Oblique Intercostal Block: Anatomic Evaluation and Case Series

Abstract

Study objective: We report a modified block technique aimed at obtaining upper midline and lateral abdominal wall analgesia: the external oblique intercostal (EOI) block.

Design: A cadaveric study and retrospective cohort study assessing the potential analgesic effect of the EOI block.

Setting: Cadaver lab and operating room.

Patients: Two unembalmed cadavers and 22 patients.

Interventions: Bilateral ultrasound-guided EOI blocks on cadavers with 29 mL of bupivacaine 0.25% with 1 mL of India ink; single-injection or continuous EOI blocks in patients.

Measurements: Dye spread in cadavers and loss of cutaneous sensation in patients.

Main results: In the cadaveric specimens, we identified consistent staining of both lateral and anterior branches of intercostal nerves from T7 to T10. We also found consistent dermatomal sensory blockade of T6-T10 at the anterior axillary line and T6-T9 at the midline in patients receiving the EOI block.

Conclusions: We demonstrate the potential mechanism of this technique with a cadaveric study that shows consistent staining of both lateral and anterior branches of intercostal nerves T7-T10. Patients who received this block exhibited consistent dermatomal sensory blockade of T6-T10 at the anterior axillary line and T6-T9 at the midline. This block can be used in multiple clinical settings for upper abdominal wall analgesia.

Keywords: Abdominal Surgery; External Oblique Intercostal Block; Intercostal Nerves; Interfascial Plane Block; Regional Anesthesia.