Our study will compare patients who underwent laparoscopic surgery for colorectal cancer with and without Erector Spinae Plane Block in terms of renal blood flow and renal function tests. In our study, which will be conducted by dividing patients into two groups, the investigators aim to demonstrate the effects of the erector spinae plane block on renal physiology by simultaneously monitoring renal blood flow during the intraoperative period using near-infrared spectroscopy and monitoring renal function in the postoperative period using NGAL, serum creatinine, and eGFR.

Our study comparing patients who did and did not undergo ESBP in terms of renal blood flow and renal function tests during laparoscopic surgeries for colorectal cancer is planned to be conducted at Kayseri City Hospital with volunteer patients.

The erector spinae plane block (ESP) is a block that is easy to perform with ultrasound (USG) guidance and has a relatively low risk of mechanical complications. It has quickly become popular and is used in various indications in anesthesiology and resuscitation clinics.

The total number of volunteers expected to participate in this study is 60. Patients will be randomly assigned to two groups using a sealed envelope method. The number of volunteers determined for each group is 30.

Patients will be interviewed before the operation and informed about the operation and the procedure to be performed. After reading and approving the informed consent form, patients to be included in the study will be divided into two groups using the sealed envelope method. Group 1 will receive ESP block, while Group 2 will be the control group and will not receive any block.

All patients will be monitored throughout the operation using invasive blood pressure, ECG, and pulse oximetry. Following preoxygenation, induction will be administered with intravenous propofol (2 mg/kg), fentanyl 1 µg/kg, and rocuronium (0.6 mg/kg) injections. After tracheal intubation, an arterial catheter will be placed in the radial artery to continuously monitor blood pressure. Anesthesia maintenance will be achieved with inhaled sevoflurane and intravenous remifentanil infusion. After induction, patients will be placed in the left-right lateral decubitus position, and bilateral blocks will be performed with ultrasound guidance.

Group 1: ESP block, 0.5% bupivacaine 0.2-0.4 ml/kg will be administered. Group 2: Patient group without block.

After ESBP application, the 'Near infrared spectroscopy' device will be placed on the bilateral 9-10th posterior costal region (flank region) of the patients in a manner suitable for observing renal blood flow. Monitoring will be performed throughout the operation and recorded on the follow-up form. N-GAL, serum creatinine, and eGFR values will be measured in both groups during the preoperative and postoperative periods (at 2, 6, and 24 hours).

Once the expected number of patients is reached, the data obtained will be statistically evaluated and recorded.

After the data is collected, it will be processed for statistical evaluation.

Inclusion Criteria:

• Age: 35-75 years old
• Colorectal cancer surgery must be planned by a physician
• No infection in the injection site
• No history of any disease related to clotting or bleeding time
• The patient must be a volunteer
• No history of local anesthetic allergy

Exclusion Criteria:

• Being under 18 years of age
• Having a systemic infection or infection at the injection site
• Having any disease related to bleeding time and clotting
• Having a history of local anesthetic allergy
• Patient refusal (ESPB for analgesic purposes)
• Patients with a Body Mass Index (BMI) of 30 or above

Patients will be randomized using the sealed envelope method. The anesthesiologist performing the procedure will be fixed, and the person keeping records will always be another anesthesiologist.