Study Design and Patient: This prospective randomized study was conducted with the approval of the local ethics committee of the Bolu Abant Izzet Baysal University in Turkey (Approval date 03/11/2020; Decision no. 2020/243). All patients who agreed to participate in the study were informed about the purpose of the study and the anesthesia method to be used, and their written consent was obtained. Sixty-five patients, aged 50-75 years, at the risk of American Society of Anesthesiologists (ASA) III, who was planned off-pump CABG surgery were invited to the study between November 2020 and April 2021. In the preoperative evaluation, patients with hypersensitivity to the drugs to be used or the substances in their composition, having moderate or severe left ventricular dysfunction, bleeding disorders, liver and kidney failure, chronic obstructive pulmonary disease, patients who do not have sufficient intellectual capacity to use the PCA device, and who refused to participate in the study were excluded from the study. In the intraoperative period, patients who needed a cardiopulmonary bypass pump and those who needed an aortic balloon pump support were excluded from the study. In the postoperative period, patients for whom the extubation duration was longer than four hours and those who required re-exploration were excluded from the study The groups were randomized; It was divided into Group E (ESP Group) and Group C (Control Group). The Ramdom.org program (https://www.random.org/lists/?mode=advanced) was used for the randomization of the groups. Demographic data (gender, age, weight, height, body mass index (BMI)) of all patients were recorded. The patients were taken to the operating room without premedication. and electrocardiography (ECG), heart rate (HR) Sist, and peripheral oxygen saturation (SpO2) values were monitored and two peripheral vascular accesses were established with an 18-gauge intravenous (IV) cannula. To provide continuous arterial blood pressure monitoring, the radial artery was cannulated by applying topical anesthesia after the Allen test.

Interventions In Group E patients, a prone position was given before general anesthesia induction. Compliance with the rules of asepsis-antisepsis was achieved. A Sonosite-180 Plus model USG (L38/10-5 MHz Transducer, SonoSite Inc., Bothell, WA 98021 USA) was used for the intervention. An adjusted linear probe was used, which was set to a depth of 2-5 cm and a frequency of 10-15 MHz. The probe was placed craniocaudally in the parasagittal plane approximately 3 cm lateral to the T5 spinous process. The T5 transverse process is detected using a planal approach. Before the procedure, the skin, subcutaneous tissue, trapezius, rhomboid, and erector spinae muscles were identified, and local anesthesia was administered using 2% lidocaine (Aritmal 2% ampoule, Osel Medicine Istanbul, Turkey). When the block needle (Stimuplex B. Braun R, Melsungen, Germany) touched the transverse process, 0.5-1 mL of the 0.9% NaCl test dose was administered between the erector spinae muscle fascia and the vertebral transverse process, and the needle location was confirmed. Then, 20 ml of 0.25% bupivacaine (Buvasin 0.5% Vem Medicine Istanbul, Turkey) was administered to this area, and an ESP block was applied (Figure 1). The same procedure was performed on the opposite side, and a bilateral ESP block was applied. The block was considered successful when cold loss developed. No preoperative procedure was applied to the Group C patients.

Anesthetic Management For the induction of general anesthesia, 2 µg/kg fentanyl (Talinat 50 mcg/ml VEM İlaç San. ve Tic. A.Ş. İstanbul, Turkey), 2 mg/kg propofol (Propofol Lipuro 1% 10mg/ml ampoule, B. Braun, Melsungen, Germany), and 0.6 mg/kg rocuronium (Esmeron 50mg/5ml Merck Sharp Dohme İlaçları Ltd. Şti. Levent/Istanbul) were given intravenously and the patient was intubated after adequate muscle relaxation was achieved. Then, central venous access was achieved. For anesthesia maintenance, 2% sevoflurane (Sevorane® Liquid 100%, AbbVie, Queenborough Kent, England) was used in 50% air and 50% oxygen. Fentanyl (0.5-2 mcg/kg) was administered 1-2 minutes before the thorax incision. An additional 1-2 mcg/kg of intravenous (IV) fentanyl was administered to patients with a 20% increase in blood pressure or heart rate. After induction, 1 mcg/kg fentanyl, and 0.25 mg/kg rocuronium were administered at half-hour intervals in both groups. Before cross-clamping the ascending aorta, the systolic pressure had aimed to be below 100 mmHg. To maintain a systolic pressure below 100 mmHg, patients were administered 1-2 mcg/kg fentanyl when necessary. Intraoperative fentanyl consumption was recorded. During anesthesia, intermittent arterial blood gas monitoring was performed on all patients. The anesthesia and surgery durations of the patients were recorded, and they were taken to the intensive care unit (ICU) as intubated after the operation. The patients were extubated within 4 hours postoperatively. Patient-controlled analgesia devices were applied to all patients after extubation. Tramadol HCl (Tramosel 100 mg/2 ml Haver Pharma İlaç A.Ş, Istanbul/Turkey) was adjusted as IV bolus 20 mg doses of tramadol HCl every time a button was pressed, at a concentration of 5mg/ml. The device was adjusted to allow a maximum dose of 400 mg in 24 hours, with a lock-in time of 20 minutes; total tramadol consumption was recorded. After extubation, VAS values were recorded at the 1st, 2nd, 4th, 8th, 12th, 18th, 24th, 36th, and 48th postoperative hours. During the 0-1, 1-12, 12-24, 24-36, and 36-48 time zones, heart rate, systolic blood pressure, mean blood pressure, diastolic blood pressure, and peripheral oxygen saturation were monitored and recorded. Nausea, vomiting, pruritus, desaturation, urinary retention, and other side effects were followed up and recorded in the patient follow-up after extubation. Postoperative nausea and vomiting were treated with 4mg of ondansetron (IV) (Ondaren 4mg/2ml Vem İlaç A.Ş Istanbul, Turkey), and rash and itching with 45.5 mg of pheniramine (IV) (Avil amp 45.5mg/2ml Sandoz İlaç A.Ş. Istanbul/Turkey). When the VAS was above four, IV 0.05 mg/kg morphine (Morphine HCL® 0.01 g/ml amp Galen İlaç A.Ş./Turkey) was administered as rescue analgesia. The extubation and ICU discharge times of the patients in both groups were recorded