Anatomical evaluation of the superficial parasternal intercostal plane block.

Background and objectives: Few cadaveric studies have evaluated the dye spread with superficial parasternal intercostal plane (SPIP) blocks. In this study, we examined the dye spread of an ultrasound-guided SPIP block in a human cadaveric model with single and double injection techniques.

Methods: Seven single and four double ultrasound-guided SPIP blocks were performed in seven unembalmed human cadavers using an in-plane approach with the transducer oriented parasagitally 1 cm lateral to the sternum. For the single SPIP, 20 mL of 0.166% methylene blue was injected in the second or third intercostal space into the plane between the Pec major muscle and internal intercostal muscles. For the double SPIP, 10 mL of 0.166% methylene blue was injected in the SPIP at one intercostal space with an additional 10 mL injected in the SPIP two intercostal spaces caudally. The extent of dye spread was documented.

Results: For all SPIP injections, there was consistent mediolateral spread from the sternum to the mid-clavicular line, with many extending laterally to the anterior axillary line. There was craniocaudal spread to a median of 2 intercostal muscles with a single SPIP and 3 intercostal muscles with a double SPIP. There was a median spread to 1 intercostal nerve for the single SPIP and 1.5 intercostal nerves with the double SPIP.

Conclusions: The SPIP block demonstrated limited spread in this cadaver study. A single injection of this block may be of limited value and multiple SPIP injections may be needed to have adequate spread for anterior thoracic procedures.