Efficacy of Hyaluronidase Added to Bupivacaine in Ultrasound-guided Erector Spinae Plane Block in Percutaneous Nephrolithotomy.

• During mask preoxygenation, patients baseline hemodynamic parameters will be recorded regarding blood pressure and heart rate.
• General anesthesia will be standardized for all patients with : 2 µg / kg fentanyl, 2 mg/kg 2% propofol then 0.5 mg/kg atracuriam will be administered for muscle relaxation.
• Patients will be intubated and lungs mechanically ventilated to maintain end-tidal CO2 between 30 to 35 mmHg. Fresh gas flow oxygen in air 30-40% at a rate of 3 L/min .
• The patients will receive 1.2 % MAC of isoflurane .
• Top- up doses of 0.15 mg/kg atracurium will be given to maintain intraoperative muscle relaxation.
• In all patients , insufflation will be under pressure of 15 mmHg or less .
• The surgical time in all surgical procedures will be fixed in the range of two hours and by the same surgical team.

After the patient will be generally anesthesized and before starting the operation , the erector spinae plane block will be performed .

• Patients will be randomly allocated to one of the two groups and the study will be double blinded where neither the operator nor the patients know which group will be . The syringes will be prepared by the other investigators.

. In group l : ESPB with bupivacaine 0.25% (30 ml volume : 15 ml saline Plus 15 ml plain bupivacaine ) .

In group ll : ESPB with plain bupivacaine 0.25% and hyaluronidase ( 14 ml saline \& 15 ml plain bupivacaine 0.25% Plus 150 units of hyaluronidase which is equal 1 ml ) .

ESP block is most often performed using an in-plane ultrasound-guided technique. It is a paraspinal fascial plane block in which the needle placement is between the erector spinae muscle and the thoracic transverse processes, and a local anesthetic is administered, blocking the dorsal and ventral rami of the thoracic and abdominal spinal nerves (4).

USG-ESPB will be performed with the patient is in lateral position,The curvilinear ultrasound transducer should be placed in a cephalocaudal orientation over the midline of the back at the desired level. The probe should then slowly be moved laterally until the transverse process is visible. The transverse process requires differentiation from the rib at that level. The transverse process will be more superficial and wider, while the rib will be deeper and thinner. Upon verification of the transverse process, the trapezius muscle, rhomboid major muscle (if performing at T5 level or higher), and erector spinae muscle should be identified superficial to the transverse process. The Tuohy needle should be inserted superior to the ultrasound probe using an in-plane approach in the cephalad to caudal direction. The bevel of the Tuohy needle should point posteriorly and inferiorly, and advance under ultrasound guidance through the trapezius muscle, rhomboid major muscle, and erector spinae muscle and towards the transverse process; once the needle tip is below the erector spinae muscle, a small bolus of local anesthetic should be given through the Tuohy needle. The erector spinae muscle should be visualized, separating from the transverse process. This separation from the transverse process confirms the proper needle position. The local anesthetic should then be injected in 5 ml increments, with aspiration after every 5 ml to prevent intravascular injection.

• It is important to visualize the pleura very clearly at all times. The hyperechoic line of the pleura and underlying hyperechoic air artifacts move with respiration.
• Dose of hyaluronidase :

The minimum and maximum effective doses of hyaluronidase are unknown. The doses used range from 0.75 IU/mL to 300 IU/m.(8) (Table 3)