The goal of clinical trial is to compare in of analgesic efficacy of sacrale erector spinae plane (ESP) block and caudal block in participants undergoing hypospadias surgery. Investigators will include children between the ages of 6 months and 7 years in the 1st and 2nd categories in the ASA.

In this study, investigators seek answers to the following questions:

Which of the sacral (ESP) block and caudal block applied to participants undergoing hypospadias surgery has higher postoperative analgesic efficiency than the other? Which of the sacral ESP block and caudal block applied to participants undergoing hypospadias surgery is superior in duration of analgesia? After general anesthesia is administered to the participants, one of the 2 blocks will be administered in a randomized manner and the relevant data will be recorded. This research will be conducted in a single center as a prospective randomized controlled study. It was planned to include 60 participnts from the ASA I-II pediatric participants aged between 6 months and 7 years, who will undergo hypospadias surgery between December 2022-December 2023, and randomization will be done by closed envelope method. Two groups with sacral ESP and caudal block will be formed, each with 30 participants.

This study will be conducted as a prospective, randomized controlled trial at a single center between December 2022 and December 2023. Sixty pediatric participants, aged 6 months to 7 years, classified as ASA I-II, who are scheduled for hypospadias surgery, will be included. Participants will be randomized into two groups: ESP block group and caudal block group, with 30 participants in each group. Randomization will be done using a sealed envelope technique based on computer-generated random numbers..

The study was planned to be performed as a double blind. Sacral ESP and caudal block will be administered by an anesthesiologist not responsible for the perioperative and postoperative management of the participants. A second anesthesiologist, who will be in charge of monitoring and data recording, will be unaware of the participants' group assignments. Additionally, parents, surgeons, and other personnel involved in the data collection process will be unaware of the group to which the child is assigned. Surgeons will not be present in the operating room while the anesthesiologist administers the block (sacral ESP block or caudal block). All participants will undergo aseptic skin preparation using Betadine. Since bandages will be applied to two points, the actual injection site will not be known.

The age, height, weight, gender and ASA scores of the participants in both groups will be recorded.

After the participants are taken to the operation table, standard monitoring will be performed. Heart rate (HR), mean arterial pressure (MAP), body temperature, peripheral oxygen saturation (SpO2) will be monitored and all parameters before surgical incision, after surgical incision, before awakening, postoperative 5 and 30 minutes will be recorded.

All participants will be placed in an IV cannula using 8% sevoflurane in 50/50 O2 / air for 2 - 4 minutes with a face mask, followed by induction of inhaled anesthesia. All participants will be placed in I-gel (supraglottic airway vehicle) by performing routine induction of general anesthesia with propofol 2-3 mg kg-1, fentanyl 1 mcg kg-1. Participants will have mechanical ventilatory support and tidal volume will be set to 8- 10 ml/kg and minute breathing will be set to 16-26. The end tidal carbon dioxide will be kept between 35-40 mmHg. Anesthesia maintenance will be provided with a starting dose of sevoflurane 2% and IV remifentanil 0.05 mcg kg-1 min-1 with a flow of 3 Lt min-1, an Oxygen/air mixture. >20% increase in intraoperative heart rate will be evaluated as pain and remifentanil dose will be increased and the need for remifentanil used intraoperatively will be recorded.

Group ESP (n=30) participants will be given a lateral decubitus position under general anesthesia before the operation and sacral ESP block will be performed accompanied by ultrasound. Group C (n=30) participants who will undergo caudal block will also be given a lateral decubitus position and ultrasound-guided block will be performed.

After 15 minutes of block surgery will be initiated. All operations will be performed by the same experienced team with the same surgical technique.

Near the end of the operation, 15 mg kg-1 IV paracetamol will be given. At the end of the operation, the duration of operation will be recorded.

Pain scoring system Face, Legs, Activity, Cry, Consolability (FLACC) will be recorded in 5th and 30th minutes and 1st, 2nd, 4th, 6th, 12th, 24th hours.

At the end of the operation, the time when there is a need for analgesia will be evaluated as "the first need for analgesia (hour)".

Total amount of additional analgesia (oral paracetamol, mg), amount of rescue analgesia (oral ibuprofen, mg), participants' relative satisfaction (1-Not satisfied, 2-Satisfied, 3-Very satisfied) will be recorded.

Motor weakness, neurological deficit, urinary retention, nausea, vomiting, hypotension, bradycardia, itching, local anesthetic toxicity and bleeding that may occur will be recorded.

Inclusion Criteria:

• American Society of Anesthesiology (ASA) I-II group
• 6 months to 7 years old
• Paediatric age group patients who will undergo hypospadias surgery under general anesthesia

Exclusion Criteria:

• ASA III - IV patient group
• Patients who were operated on urgently
• Patient relatives who did not give consent
• Presence of local anesthetic allergy
• Presence of infection in the area to be blocked
• Presence of coagulation disorder
• Severe organ failure
• Pre-existing neurological deficit
• Mental Retardation
• Anatomical Deformity

The study was planned to be performed as a double blind. User sacral ESP and caudal block will be administered by an anesthesiologist not responsible for the perioperative and postoperative management of the patients. A second anesthesiologist, who will be in charge of patient monitoring and data recording, will be unaware of the patients' group assignments. Additionally, parents, surgeons, and other personnel involved in the data collection process will be unaware of the group to which the child is assigned. Surgeons will not be present in the operating room while the anesthesiologist administers the block (sacral ESP block or caudal block). All patients will undergo aseptic skin preparation using Betadine. Since bandages will be applied to two points, the actual injection site will not be known.