Comparison of the effects of modified pectoral nerve block and erector spinae plane block on postoperative pain scores and opioid consumption after radical mastectomy

In the operating room, all of the patients will receive a standard monitoring including electrocardiography, non-invasive blood pressure, peripheral oxygen saturation and bi-spectral index monitoring. An anesthesiologist will perform anesthesia inductions with intravenous 2-3 mg kg-1 propofol, 1 mcg kg-1 fentanyl and 0.6 mg kg-1 rocuronium bromide. After each patient's BIS score decreases to 40–60, endotracheal intubation will be performed. Immediately after intubation, the patients in the first group (Group ESP) will be placed in lateral decubitus position. The anesthesiologist of the operating room will locate a high-frequency linear ultrasound probe in longitudinal orientation at the level of T4 spinous process and then place 3 cm laterally from the midline from the midline to the side of the surgery. The ultrasound landmark T4 transverse process will be identified. Under aseptic conditions, the anesthesiologist will insert a 80 mm 21-gauge block needle in-plane at an angle of 30-40 degrees in cranial-to-caudal direction until the tip contact the T4 transverse process. After the hydrodissection with 2-3 mL of isotonic saline solution confirms correct needle tip position, 20 mL of 0.25% bupivacaine will be injected in the interfascial plane between rhomboideus major and erector spinae muscle. All of the patients will receive 4-6% end-tidal desflurane in the 3 lt of 40% O2 and 60% N2O for maintenance of anesthesia. The minimum alveolar concentration of desflurane will be targeted to reach a BIS value between 40-60. At the end of the operation, postoperative analgesia will be maintained with tramadol infusion by using a patient controlled analgesia (PCA) device in all of the patients. The PCA device will administer 20 mg hour-1Tramadol as infusion, 10 mg bolus dose with a 15 minute lock-time.