Optimal techniques of ultrasound-guided superficial and deep parasternal intercostal plane blocks: a cadaveric study

Abstract

Introduction: The optimal techniques of a parasternal intercostal plane (PIP) block to cover the T2-T6 intercostal nerves have not been elucidated. This pilot cadaveric study aims to determine the optimal injection techniques that achieve a consistent dye spread over the second to sixth intercostal spaces after both ultrasound-guided superficial and deep PIP blocks. We also investigated the presence of the transversus thoracis muscle at the first to sixth intercostal spaces and its sonographic identification agreement, as well as the location of the internal thoracic artery in relation to the lateral border of the sternum.

Methods: Ultrasound-guided superficial or deep PIP blocks with single, double, or triple injections were applied in 24 hemithoraces (three hemithoraces per technique). A total volume of dye for all techniques was 20 mL. On dissection, dye distribution over the first to sixth intercostal spaces, the presence of the transversus thoracis muscle at each intercostal space and the distance of the internal thoracic artery from the lateral sternal border were recorded.

Results: The transversus thoracis muscles were consistently found at the second to sixth intercostal spaces, and the agreement between sonographic identification and the presence of the transversus thoracis muscles was >80% at the second to fifth intercostal spaces. The internal thoracic artery is located medial to the halfway between the sternal border and costochondral junction along the second to sixth intercostal spaces. Dye spread following the superficial PIP block was more localized than the deep PIP block. For both approaches, the more numbers of injections rendered a wider dye distribution. The numbers of stained intercostal spaces after superficial block at the second, fourth, and fifth intercostal spaces, and deep block at the third and fifth intercostal spaces were 5.3±1.2 and 5.7±0.6 levels, respectively.

Conclusion: Triple injections at the second, fourth, and fifth intercostal spaces for the superficial approach and double injections at the third and fifth intercostal spaces for the deep approach were optimal techniques of the PIP blocks.

Keywords: nerve block; regional anesthesia; ultrasonography.