Investigation of the effect of erector spinae plane block, a new pain-relieving method for the relief of post-operative pain in patients whose part of the liver will be removed.

ESP Block Application:All blocks will be performed by an anesthesiologist experienced in the block approximately 30 minutes before anesthesia induction. The block will be made at the level of the T8 vertebra. The T7 vertebra that corresponds to the level of the lower ends of the scapula will be identified and the T8 vertebra below one level will be detected by palpation. Patients will be laid in prone position and skin preparation will be done with 10% povidone iodine. Skin-subcutaneous anesthesia will be provided with 3 ml 2% lidocaine at the target injection site. T8 spinous process in the midline and horizontal plane will be displayed first by using a linear probe coated with a sterile drape at 8 mHz frequency accompanied by ultrasonography. The probe is then turned to the longitudinal plane, approximately 3 cm from the midline, the transverse process on the left lateral and the erector spina muscle will be displayed on it. The 22-gauge, 80-mm block needle will be advanced cranio-caudal as in-plane and the transverse process will be touched. Then, after the needle is minimally retracted, 20 ml 0.375% bupivacaine hydrochloride + 4 mg dexamethasone will be injected, and simultaneous local anesthetic emission will be monitored by ultrasonography. By applying the same procedure to the right side, bilateral ESP block will be performed. Loss of sensation of warm-cold sensation below and above the bilateral T8 dermatome level 20 minutes after the block is made will be considered as block success. Participants in this group will also receive PCA postoperatively.