This study will evaluate the effect of adding dexmedetomidine to bupivacaine compared to ketamine in the caudal block on perioperative analgesia in patients undergoing lumbosacral surgeries under general anesthesia.

Preoperative settings:

All participants will be clinically assessed (history, duration of illness and medications especially analgesic history) and routine preoperative investigations will be done; CBC, Coagulation profile, liver function tests, kidney function tests, random blood sugar and ECG.

Also preoperatively, participants will be trained how to use visual analog scale (VAS) to assess pain severity. Scores will be recorded by making a handwritten mark on a 10-cm line that represents a continuum between "no pain" on the left end (0 cm) of the scale and the "worst pain" on the right end of the scale (10 cm).

Intraoperative settings and technique:

On arrival of the participant to the operative room, standard monitoring including electrocardiography, non-invasive blood pressure, and pulse oximetry will be applied.

Baseline parameters of vital data and oxygen saturation will be recorded. An Intravenous (IV) line will be inserted. Premedication using IV injection of Midazolam 0.02mg/kg, Granisetron 3mg and Pantoprazole 40 mg will be administered slowly IV.

For all groups, induction of general anesthesia will be performed using IV injection of Fentanyl 2μg/kg, Propofol 1mg/kg and Atracurium 0.5mg/kg.

Specific equipment required: 18G Tuohy epidural needle, Loss of resistance epidural syringe, skin antiseptic solution, sterile gloves and portable C-arm fluoroscopy.

After securing the airway, patient stabilization and proper positioning in the prone position, the caudal block will be performed.

An 18-gauge Tuohy-type needle will be inserted in the midline into the caudal canal under C-arm guidance. A slight "snap" feeling may be appreciated when the advancing needle pierces the sacrococcygeal ligament. Once the needle reaches the ventral wall of the sacral canal, it will be slowly withdrawn and reoriented, directing it more cranially (by the depressing hub and advancing) for further insertion into the canal.

The investigators will utilize the anteroposterior view once the epidural needle is safely situated within the canal. In this projection, the intermediate sacral crests will appear as opaque vertical lines on either side of the midline. The sacral foramina will be visualized as translucent and nearly circular areas lateral to the intermediate sacral crests. A syringe loaded with 3-4 ml of iohexol 180mgI/ml contrast material will be used to document epidural spread and exclude intravascular injection.

For all groups, using IV injection of Paracetamol (15 mg/ kg) and Ketorolac (30 mg) as a part of multimodal analgesia will be administered.

Intraoperative bradycardia (HR <60 beats/min) will be managed with atropine 0.01 mg/kg and hypotension (systolic arterial pressure <90 mmHg) will be managed with 20 ml/kg lactated Ringer and ephedrine 5mg increments if needed. If the patient has tachycardia (>20% of the baseline) and/or hypertension (MAP >20% of the baseline), 50μg fentanyl will be given IV slowly.

At the end of surgery, anesthesia will be discontinued and the muscle relaxant will be reversed by neostigmine 0.05mg/kg, atropine 0.02mg/kg and the patient will be transferred to PACU.

HR, MAP and oxygen saturation will be measured upon arrival to the PACU and after 5 minutes, then every 10 minutes till the patient discharge from PACU.

Caudal Block Technique:

All patients will be in prone position. A dry gauze swab will be placed in the intergluteal cleft to protect the anal area and genitalia from povidone iodine which will be used to disinfect the skin. Anatomical landmarks will be next assessed. A triangle may be marked on the skin over the sacrum, using the posterior superior iliac spines (PSISs) as the base, with the apex pointing inferiorly (caudally). Normally, this apex sits over or immediately adjacent to the sacral hiatus. Once the hiatus is marked, the tip of the index finger will be placed on the tip of the coccyx in the intergluteal cleft while the thumb of the same hand palpates the two sacral cornua located 3-4 cm more rostrally at the upper end of the intergluteal cleft. The sacral cornua may be identified by gently moving the palpating index finger from side to side. The palpating thumb should sink into the hollow between the two cornua, as if between two knuckles of a fist. Sterile skin preparation and draping of the entire region will be performed in the usual fashion.

Fluoroscopy will be utilized, a lateral view will be obtained to demonstrate the anatomic boundaries of the sacral canal. The caudal canal will appear as a translucent layer posterior to the sacral segments. The median sacral crest is visualized as an opaque line posterior to the caudal canal. The sacral hiatus is usually visualized as a translucent opening at the base of the caudal canal. The coccyx may be seen articulating with the inferior surface of the sacrum.

In Group C: The participants will receive isobaric bupivacaine (0.125%) total volume of 20 ml.

In Group D: The participants will receive isobaric bupivacaine (0.125%) total volume of 18 ml + 2μg/kg dexmedetomidine total volume of 2 ml.

In Group K: The participants will receive isobaric bupivacaine (0.125%) total volume of 18 ml + 1mg/kg ketamine total volume of 2 ml.

Postoperative settings:

After the patient will be discharged from the operating room, (VAS) will be used to assess the acute postoperative pain. The (VAS) will be recorded at intervals 0 (at PACU), 2, 4, 6, 8, 12, 16 and 24 hours postoperatively.

All patients will receive IV ketorolac 30 mg and paracetamol 1 gm every 8 hours.

If VAS is ≥ 3 postoperatively, a rescue drug will be given; IV morphine (0.01mg/kg) and will be repeated on demand maximally every 6 hours. Time and dose will be recorded.

Any side effects will be recorded as hypotension (systolic arterial pressure <90 mmHg), arrhythmia, bradycardia (HR <60 beats/min), nausea or vomiting, pruritis or any other complications.

Atropine 0.01 mg/kg will be given in response to bradycardia and 20 ml/kg lactated Ringer will be given in response to hypotension.

In the surgical ward, the following will be recorded in the three groups :

Pain intensity (using VAS) will be assessed every 2 hours in the first 8 hours then every 4 hours in the next 8 hours then at 24 hours postoperatively.

Time for first rescue analgesia. Total morphine consumption in the first 24 hours. Postoperative nausea and vomiting. Vital data every 2 hours in the first 8 hours then every 4 hours in the next 8 hours then at 24 hours postoperatively.

All parameters will be collected by a data assessor who will be blinded to the drug injected in the caudal block.

Inclusion Criteria:

• Age 21-60 years.
• Sex: Both sexes.
• American Society of Anesthesiologists (ASA) Physical Status Class-I and II.
• Scheduled for lumbosacral surgery under General Anesthesia.

Exclusion Criteria:

• Declining to give written informed consent or patients with significant cognitive dysfunction that hinders informed consent.
• History of allergy to the medications used in the study.
• Contraindications to regional anesthesia (including coagulopathy and local infection).
• History of recent analgesic intake or abuse.
• Pregnancy or lactating mothers.