A Comparison of the Analgesic Effects of Rectus Sheath and Transversus Thoracis Plane Blocks (ABC Blocks) Versus Saline Injection for Median Sternotomy: a Prospective, Randomized Controlled Trial.

Subjects will be randomized on the morning of surgery to receive either "anterior blocks for cardiac surgery" or "ABC blocks" using 60 mL of local anesthetic mixture (20 mL of liposomal bupivacaine plus 40 mL of 0.25% bupivacaine) or a sham saline ABC block (60 mL). All subjects will receive standard of care anesthetic regimen for their cardiac surgery at the discretion of his/her attending anesthesiologist. 40 mL of the solution will be administered in the parasternal intercostal space, and 20 mL will be placed in the rectus sheath in the epigastric region.

For the parasternal blocks, a linear high frequency ultrasound probe will be placed parasagitally at the T2-3 level approximately 3cm lateral to the mid-sternum, and all relevant structures will be identified, including the pectoralis major muscle, internal intercostal muscle, ribs, pleura, and any vasculature, including the internal mammary artery and vein. Color Doppler will be used confirm the location of vasculature.

After skin local anesthetic infiltration, a 10 cm 21G insulated block needle (Sonoplex, Pajunk Medical Systems, Norcross, GA) will be inserted from the inferior aspect of the ultrasound probe in a caudal to cranial direction and aligned with the ultrasound scanning plane (in-plane approach). In this way, both the needle shaft and tip can be visualized as the needle approaches the plane between the pectus major and intercostal muscles. The needle will be redirected as needed. Once satisfactory position of the needle time is confirmed and after frequent negative aspiration, 10 mL of study solution will be slowly injected. This injection will be repeated at the T4-5 interspace. Spread of local anesthetic will be documented in the appropriate plane in real time. This procedure will be performed bilaterally.

For the rectus sheath blocks, a linear high frequency ultrasound probe will be placed in a transverse position in the midline, just inferior to the xiphoid process. The probe will be moved laterally to visualize the lateral edge of the rectus abdominis muscle. A 10 cm 21G insulated block needle will be inserted from the lateral aspect of the ultrasound probe in a lateral to medial direction until visualized deep to the muscle immediately adjacent to the posterior rectus sheath. After negative aspiration, 10 mL of study solution will be slowly injected into this plane. This procedure will then be repeated on the contralateral side

All nerve blocks will be performed by a trainee supervised by an anesthesiologist experienced in regional anesthesia. The anesthesiology team and in the OR will be blinded to group allocation.