Lumbar spine surgery causes intense post-op pain, peaking within 12 hours and improving by day three. Traditional spinal procedures involve extensive tissue dissection, leading to severe pain and potential complications like delayed mobilization, respiratory issues, and chronic pain. Effective pain management is crucial. Opioid-based relief is standard but comes with side effects (nausea, respiratory depression), increasing hospital stays and costs.

Dexmedetomidine (DEX) is an alpha-2 adrenergic receptor agonist that enhances nerve block duration when combined with local anesthetics (LAs). It works by inhibiting sodium and potassium channels, leading to prolonged hyperpolarization.

Regional nerve blocks, such as thoracic epidurals and fascial plane blocks, improve postoperative pain management and help reduce opioid use, minimizing complications. Various techniques, including ESP blocks, paravertebral Block (PVB), and Serratus anterior Block (SAB) have been explored for acute pain relief.

The Erector Spinae Plane Block (ESPB), initially used for thoracic neuropathic pain, has expanded to thoracic, breast, and abdominal surgeries.

The ESP block is done by injecting a local anesthetic between the transverse process and the erector spinae muscle. Ultrasound guidance helps visualize the spread of the anesthetic and the surrounding anatomy. Previous studies indicate that the ESP block can effectively relieve pain after lumbar spine surgery and may reduce postoperative opioid use when local anesthetics are applied to the wound and deep tissues. Based on this, performing the ESP block directly by the surgical team, using a local anesthetic between the erector spinae muscle and transverse process with direct view and free hand, may yield similar results to the ultrasound guided technique. The current study aims to evaluate the analgesic efficacy of Ultrasound-Guided Erector Spinae Plane Block in comparison with surgical Erector Spinae Plane Block using a mixture of bupivacaine and dexmedetomidine in lumbar Spinal fusion Surgeries.

After approval of the local institutional ethics committee and local institutional review board. Patients scheduled for elective lumbar spinal Fusion surgeries and fulfilling the inclusion criteria in Fayoum University Hospital starting from February 2025 will be enrolled in this prospective randomized study until fulfilling the sample size. The eligible participants will sign a detailed informed consent before recruitment.

Randomization will be done using computer-generated random numbers placed in separate opaque envelopes and opened by the anesthesiologist just before induction of anesthesia, eligible patients will be randomized with 1:1 allocation ratio into two groups:

• The surgical ESPB group (SB)
• The Ultrasound guided ESPB group (UB) Both the anesthesiologist and the surgeons performing the US guided ESP block and surgical ESP block will not be further involved in the study. Another anesthesiologist will be responsible for further patient care and data collection. This anesthesiologist and the patient will be blinded from the group assignments.

General anesthesia:

Upon arrival at the operating theatre, all patients will be monitored using electrocardiography, pulse-oximetry, capnography, and Noninvasive blood pressure (NIBP). After routine history, examination, and review of laboratory results, General anesthesia will be induced with intravenous propofol (2 mg/kg), fentanyl (1 μg/kg), and atracurium (0.5mg/kg). After that, patients will be intubated and placed in a prone position. Anesthesia will be maintained using IV atracurium and inhalational anesthesia (isoflurane) in an oxygen and fresh air mixture. All patients will receive intravenous Ketorolac (30 mg), Nalbuphine (10 mg), and Ondansetron 8 mg approximately 30 min before the end of the surgery.

Block technique:

For patients in Group UB, an ultrasound-guided ESP block will be performed after the surgical incision is closed and before extubation, while the patient remains in the prone position. A linear high-frequency transducer (L6-12 linear array transducer (6-12 MHz) on GE Healthcare logiq p7, made in Korea) will be positioned in a sagittal orientation, 4 cm lateral to the L3 transverse process. A 22 G × 88 mm block needle will be inserted in the craniocaudal direction, with the needle tip placed beneath the erector spinae muscle and above the hyperechoic transverse process. The needle tip position will be confirmed via saline injection. Once correct needle placement is verified, 40 mL of 0.25% bupivacaine, combined with 0.5 μg/kg dexmedetomidine 15 will be administered divided on both sides. For patients in group SB, the injectate will be prepared with the help of the anesthetist by adding 0.5 μg/kg dexmedetomidine to 40 mL of 0.25% bupivacaine. This volume will be divided into 8 injections, four 5 ml injections on each side. The surgeons will perform the block just before starting the wound closure stage. The surgical ESP block technique consists of injections at four bilateral levels, starting from one level above the operated vertebra and covering all surgical segments using a 22G × 88 mm needle. The needle will be inserted to contact the transverse process, and the injectate will be delivered between the erector spinae muscle and the transverse process at each level.

Postoperative pain management:

After discharge to ward, all patients will receive paracetamol 1g / 8hrs, ketorolac 30 mg/ 12hrs and nalbuphine 5mg as a rescue analgesia. The patient's pain will be evaluated using a Visual Analog Scale (VAS) where 0 denotes no pain, and 10 represents the most intense pain ever experienced. Dynamic and static VAS scores will be recorded in the postoperative period at 1, 4, 8, 16, 24, 36 and 48 hours. Patients with VAS scores of 4 or higher will receive Nalbuphine (5 mg) for rescue analgesia.

sample size calculation and statistical analysis : Sample size was calculated using IBM SPSS 29 software for windows (IBM Co., Armonk, NY, USA). Calculation of the sample size was based on the ability to detect a difference of one point in the VAS score between the two groups based on the results of a study by Kaciroglu, A. et al. At least 23 patients are needed per group to detect this difference at α level of 0.05 and study power of 80%. We decided to recruit 26 patients per group to compensate for any possible withdrawals up to 10% and to increase the study power. The sample size calculation was based on the independent samples t test. Statistical analysis will be performed using SPSS for Windows, version 29 (IBM Corp., and Armonk, New York, USA). Descriptive statistics will be presented in the form of (mean ± SD), or (median with interquartile range) for numerical data, while numbers and percentages will be used for categorical data. Testing for normality of distribution will be done using the Shapiro-Wilk test. Categorical variables will be analyzed using Chi-square test or Fisher's exact test. Differences in parametric normally distributed numerical data will be compared using Student's t tests, While the non-parametric data will be compared using Mann Whitney U-test. Results will be considered statistically significant if the p value is less than 0.05.

Inclusion Criteria:

- American Society of Anesthesiologists (ASA) I-Ⅲ patients scheduled for elective two or three levels of lumbar spinal fusion surgeries by the same surgical team.

Exclusion Criteria:

• Patient refusal.
• Body mass index > 30 kg/m2
• Significant renal, hepatic, or cardiovascular diseases.
• History of allergy to one of the study drugs (local anesthetics, opioids, or dexmedetomidine).
• Any contraindications to regional anesthesia like local infection or abnormal coagulation function.
• Pregnant or breastfeeding women.
• Chronic opioid use, history of chronic pain, or cognitive disorders.
• Emergent surgeries.