Superficial versus deep parasternal intercostal plane blocks: cadaveric evaluation of injectate spread

Deep and superficial parasternal intercostal plane blocks provide anterior chest wall analgesia for both breast and cardiac surgery. Our primary objective of this cadaveric study was to describe the parasternal spread of deep and superficial parasternal intercostal plane blocks. Our secondary objectives were to describe needle proximity to the internal mammary artery when performing deep parasternal intercostal plane blocks, and compare lateral injectate spread and extension into the rectus sheath.We performed ultrasound-guided deep and superficial parasternal intercostal plane blocks 2 cm from the sternum at the T3-4 interspace in four fresh frozen cadavers as described in clinical studies.Parasternal spread of injectate was greater with the deep parasternal intercostal plane injection than with the superficial parasternal intercostal plane injection. The internal mammary artery was ∼3 mm away from the needle trajectory in cadaver #1 and ∼5 mm from the internal mammary artery in cadaver #2. Lateral spread extended to the midclavicular line for all deep parasternal intercostal plane blocks and beyond the midclavicular line for all superficial parasternal intercostal plane blocks. Neither block extended to the rectus sheath.A greater number of parasternal interspaces were covered with the deep parasternal intercostal plane block than with the superficial parasternal intercostal plane block when one injection was performed at the T3-4 interspace. However, considering proximity to the internal mammary artery, and potential devastating consequences of an arterial injury, we propose that the deep parasternal intercostal plane block be classified as an advanced block and that future studies focus on optimising superficial parasternal intercostal plane parasternal spread.