Thoracic surgery in children is considered a highly invasive procedure that significantly affects respiratory mechanics and cardiovascular function, resulting in substantial physiological disturbances during the perioperative period. In pediatric patients, the chest wall is structurally immature and highly compliant; therefore, impairment of ventilation after thoracic surgery may persist and predispose to atelectasis, hypoxemia, and other pulmonary complications. Inadequate postoperative analgesia may further compromise respiratory function, delay mobilization, and prolong recovery, particularly during the first 48-72 hours after thoracic surgery, when pain intensity is typically greatest. Thoracic epidural analgesia (TEA) has long been regarded as the reference technique for postoperative pain control in thoracic surgery. However, in pediatric patients, epidural catheter placement may be technically challenging and is associated with potential adverse effects such as hypotension, bradycardia, urinary retention, and other neuraxial-related complications. Thoracic epidural blockade produces bilateral sympathetic inhibition, which may lead to hemodynamic instability, particularly during thoracic surgery requiring lateral decubitus positioning and one-lung ventilation. Furthermore, epidural placement is often performed after induction of general anesthesia in children, which may limit early recognition of neurological complications. These concerns highlight the need for alternative regional analgesic techniques that provide effective analgesia while maintaining hemodynamic stability. Ultrasound-guided erector spinae plane block (ESPB) has recently emerged as a promising fascial plane block for thoracic analgesia. Injection of local anesthetic deep to the erector spinae muscle and superficial to the transverse process allows cranio-caudal spread across multiple dermatomes, potentially providing analgesia to the posterior, lateral, and anterior thoracic walls. Increasing evidence suggests that ESPB offers effective perioperative analgesia in thoracic surgery with a favorable safety profile and minimal sympathetic blockade. Continuous ESPB catheter techniques have also been reported to provide sustained postoperative analgesia comparable to epidural analgesia. Despite these encouraging findings, direct comparisons between continuous ESPB and TEA in pediatric thoracic surgery remain limited, particularly regarding hemodynamic effects, adverse events, and technical feasibility. Therefore, this randomized controlled trial was conducted to compare the analgesic efficacy and hemodynamic stability of continuous ultrasound-guided thoracic ESPB with thoracic epidural analgesia in children undergoing thoracic surgery.

This prospective, single-center, randomized controlled trial was conducted in the Department of Anesthesiology at Vietnam National Children's Hospital between January 2024 and December 2024 after approval by the institutional review board. Written informed consent was obtained from the patients' parents or legal guardians before enrollment. The study was conducted in accordance with the Declaration of Helsinki and reported following the CONSORT guidelines.

Children aged 4-16 years with ASA physical status I-II undergoing elective unilateral thoracic surgery under general anesthesia were enrolled. Eligible procedures included surgery for pulmonary cysts, mediastinal tumors, diaphragmatic hernia, lung tumors, and chest wall tumors. Patients with allergy to local anesthetics, significant hepatic, renal, or cardiovascular disease, coagulation disorders, untreated hypovolemia, infection at the puncture site, spinal or chest wall deformities, or paravertebral tumors near the puncture level were excluded. Patients were withdrawn if consent was withdrawn, if major intraoperative bleeding (>20 mL/kg) occurred, or if conversion to median sternotomy was required.

After enrollment, patients were randomly assigned in a 1:1 ratio to one of the following study groups:

• ESPB group: After induction of general anesthesia, patients underwent ultrasound-guided erector spinae plane block at the T5-T6 or T6-T7 level using a high-frequency linear probe. Following hydrodissection confirmation, 0.25% levobupivacaine (0.3 mL/kg, maximum 20 mL) was injected and a catheter was inserted for continuous postoperative analgesia.
• TEA group: After induction of general anesthesia, patients underwent thoracic epidural catheter placement at the T5-T6 or T6-T7 interspace using the loss-of-resistance technique with a Tuohy needle. After confirmation of correct placement, 0.25% levobupivacaine (0.3 mL/kg, maximum 20 mL) was administered through the epidural catheter.

General anesthesia was induced with midazolam (0.03 mg/kg), fentanyl (2 µg/kg), propofol (3 mg/kg), and atracurium (0.6 mg/kg). Following endotracheal intubation, mechanical ventilation was adjusted to maintain EtCO₂ between 30-40 mmHg. One-lung ventilation was established using an Arndt bronchial blocker under fiberoptic guidance. Anesthesia was maintained with sevoflurane in an oxygen-air mixture to maintain a bispectral index between 40 and 60. Additional fentanyl (1 µg/kg) was administered when heart rate or blood pressure increased by more than 20% from baseline values despite adequate anesthetic depth. At the end of surgery, all patients received intravenous paracetamol (15 mg/kg). Postoperative pain was assessed using the Faces Pain Scale-Revised (FPS-R) at rest and during movement. Multimodal analgesia included paracetamol every 6 hours and continuous infusion of 0.125% levobupivacaine via catheter. If FPS-R scores were ≥4, a bolus dose of levobupivacaine was administered through the catheter. Intravenous morphine (0.05 mg/kg) was used as rescue analgesia when pain remained uncontrolled

Inclusion Criteria:

• American Society of Anesthesiologists (ASA) physical status I-II.
• Diagnosis of pulmonary cyst, mediastinal tumor, diaphragmatic hernia, lung tumor, or chest wall tumor requiring unilateral thoracic surgery.

Exclusion Criteria:

• Known allergy to local anesthetics;
• Significant hepatic, renal, or cardiovascular disease;
• Coagulation disorders or untreated hypovolemia;
• Infection at the puncture site;
• Spinal or chest wall deformity or paravertebral tumors near the puncture level.
• Patients were withdrawn from the study if consent was withdrawn, if major intraoperative complications occurred such as massive bleeding (>20 mL/kg), or if conversion to median sternotomy was required during surgery.
• Patient's parents who do not consent to participate in the study