Postoperative pain is a common complication after lumbar spine surgery due to inherent tissue damage during surgical procedures.

Many analgesic options have been explored. Opioid analgesics carry the risk of respiratory depression.

Nonsteroidal anti-inflammatory drugs (NSAIDs) are popular and widely used as first-line treatment for acute pain following spinal surgery, but can provide inadequate analgesia. High doses of NSAIDs have also been linked to non-unions in spinal fusion surgery.

Patient-controlled analgesia or epidural injection analgesia are usually used. One of US guided regional anesthesia methods is the ultrasound-guided caudal block that was first described by Klocke and colleagues in 2003.

One of the more recent techniques that has been described recently is quadratus lumborum plane block(QLB),that is posterior abdominal wall fascial plane block first described by Blanco in 2007.In this study we will compare between analgesic effect of ultrasound guided caudal block to that of ultrasound guided quadratus lumborum plane block as well as safety of both modalities in adult patients undergoing lumbar spine fixation surgeries.

This study will be conducted at Fayoum University Hospital after the approval of the local institutional ethics committee and local institutional review board. The study design will be a randomized, double-blind, controlled study. A detailed informed consent form will be signed by eligible patients prior to enrollment and randomization.

Inclusion criteria:

Anesthesia procedure Patients will be randomly allocated into one of three parallel groups (37 in each group) based on sample size. Randomization will be achieved using computer-generated random numbering of each study patient. opaque sealed envelopes will be used and opened in the operating room by a anesthesia resident who will be blinded to the study. The patient and researcher who collects the data after the block will be blinded to the study group. All study outcomes will be evaluated by a dedicated anesthesiologist who will be blinded to the group allocation. Patients will be randomized into three groups.

Group (D) patients who will receive caudal block. Group (QL) patients who will receive posterior quadratus lumborum plane block. Group (C) patients who will not receive any blocks. Preoperative assessment A preoperative patient visit will be done for medical history taking, clinical examination, reassurance, and explaining the method of anesthesia. The study protocol, caudal block, quadratus lumborum plane block and the numerical pain rating score score will be explained to each patient during the preanesthetic counselling. The patient's back will be examined to detect any spinal deformities . Patients will fast for about 6 to 8 hours for solid meals , for 4 hours for non clear liquids and for 2 hours for clear liquids before surgery.

Intraoperative management Monitoring equipment will be connected to the patients included pulse oximetry, non-invasive blood pressure monitoring, five-lead electrocardiogram and capnography. IV access will be established. Patients in the three groups will receive general anesthesia after 5 minutes of pre oxygenation with 100% O2. Anesthesia will be induced with intravenous fentanyl 1mcg/kg, propofol 2 mg/kg and atracurium 0.5 mg/kg. After oral endotracheal intubation, anesthesia will be maintained with isoflurane (1.2%_1.5%) in oxygen _air mixture and atracurium 0.1mg/kg with interval about 20 min.

Block technique After stabilizing the patient hemodynamics, caudal block or quadratus lumborum plane block will be performed in the prone position prior to the skin incision after aseptic preparation of injection area.

Petit between the iliac crest and the costal margin where the trans abdominal muscle is identified . The transducer is then slid posterior until the trans abdominal muscle posterior aponeurosis is identified adjacent to Caudal block

The patient is placed in the prone position typically, a linear transducer is sufficient for the most caudal epidural injection; However, obese patients may require curved transducer. The Ultrasound transducer of (LOGIQ P7 ultrasound) will be first positioned transversely on the midline to obtain a transverse view of the sacral hiatus. The two sacral cornua appear as two hyperechoic structures ,two hyperechoic band structures are present between the two sacral cornua. The superficial is the sacrococcygeal ligament (SCL) and the deep is the dorsal surface of the sacrum. The sacral hiatus is a hypoechoic area between two band-like hyperechoic structures. At this level, the ultrasound probe is rotated 90 degrees to obtain a longitudinal view of the sacral hiatus. in the longitudinal view, the block needle will be inserted using the in plane technique .The block needle can be visualized in real time piercing the SCL entering the hiatus but cannot be visualized beyond the apex of the hiatus. It is therefore proposed to limit the extension of the needle tip beyond the tip of the sacral hiatus to 5 mm to avoid perforating the dura mater, since the distance between the tip of the sacral hiatus and the tip of the dural sac can be less than 6 mm .After the needle is inserted in the caudal canal, 20 ml of 0.25% bupivacaine will be injected. Presence of unidirectional flow, defined as dominant color on color Doppler image, In longitudinal view of sacral hiatus during injection will be reported to be predictive of successful caudal injection and comparable treatment outcomes.

Quadratus Lumborum Plane Block The patient is placed in the prone position , under aseptic conditions with the sterile convex probe is placed in a transverse view at the triangle of the QL muscle and the middle thoracolumbar fascia. The projected needle path is advanced in-plane until the needle tip is visualized between the middle thoracolumbar fascia and the QL muscle .After confirming the location of the needle with 2-3 ml of saline and then aspiration, 20 ml of 0.25% bupivacaine is injected in this plane with confirmation by visualizing hydro dissection . the procedure is applied to the opposite side using the same dose to achieve bilateral block.

Maintenance and recovery Inadequate analgesia that is predicted by increase of heart rate or mean arterial blood pressure by more than 20% of baseline will be managed by 0.5mcg/Kg of fentanyl. Total IV consumption of fentanyl will be recorded. All patients will receive 4mg ondansetron and 1 g paracetamol intravenously 30 minutes before the end of the operation. At the end of surgery, all patients will undergo reversal of muscle relaxation with neostigmine 0.05 mg/kg and atropine 0.01 mg/kg.

After recovery from anesthesia, patients will be transferred to recovery room where heart rate, respiratory rate, saturation and systolic, diastolic and mean arterial blood pressure will be monitored. Quality of analgesia will be assessed using numerical pain rating scale (NPRS) Assessment will be performed at admission to the recovery room, 1 h, 2 h, 4 h, 6 h, 8 h, 12 h, 18 h, and 24 h postoperative. Rescue analgesia in the form of pethidine 0.5 mg/kg will be administered if is pain moderate to severe according to NPRS≥4 . Time to the 1st rescue analgesic request is recorded.

Also intraoperative or postoperative complications will be recorded such as local anesthetic toxicity, hypotension, nausea, vomiting as well as neurologic complications such as weakness, numbness or any neurological deficits. Also operative time will be recorded.

Inclusion Criteria:

1. Adult patients (18-60 years old), of either gender undergoing elective lumbar spine fixation surgery.
2. Patients with American Society of Anesthesiologists (ASA) physical status I-II.

Exclusion Criteria:

1. Include patients who refuse.
2. Patients with contraindications to regional anesthesia (eg, local infection at site of injection, coagulation abnormalities).
3. Patients with spinal deformities or previous lumbar disc surgeries.
4. Allergy to local anesthetics, mental disorders as well as drug abuse.
5. BMI more than 35

Randomization will be achieved using computer-generated random numbering of each study patient. opaque sealed envelopes will be used and opened in the operating room by a anesthesia resident who will be blinded to the study. The patient and researcher who collects the data after the block will be blinded to the study group. All study outcomes will be evaluated by a dedicated anesthesiologist who will be blinded to the group allocation. Patients will be randomized into three groups.