Comparative Study Between Ketamine and Dexmedetomidine as Additives to Local Anesthetic in Ultrasound-guided Combined Sciatic and Femoral Nerve Block

The patients will be randomly classified into two groups:

Ketamine group (group K):40 ml 0.5%bupivacaine and 0.5 mg\kg ketamine, Dexmedetomidine group (group D) 40 ml 0.5% bupivacaine and 50µg\kg dexmedetomidine.

Femoral nerve block: The femoral area will be sterilized using povidone-iodine and alcohol and then drapes will be put on the patient's thigh, with the operator on the right-hand side for blocks on both sides and vice versa for a left-handed operator. The ultrasound machine will be placed on the opposite side so that the operator's line of sight, the needle, and the screen are in a straight line. The femoral area will be scanned behind the midpoint of the inguinal ligament and the depth of the image will be set at 3-5 cm and a linear high frequency 8-12MHz) probe will be placed perpendicular to the course of the femoral nerve., medial to the lateral sliding movements of the transducer-aided visualization of the pulsatile femoral artery. Structures that will be visualized: fascia iliac, femoral artery, immediately below, and lateral is the femoral nerve in a wedge-shaped space. The femoral nerve typically is hyperechoic and lies in a sulcus in the iliopsoas inferiorly. In-line insertion of the needle to reach below fascia iliaca and then a volume of 15 ml of bupivacaine will be injected to perform the block.

Sciatic nerve block: The patient will be positioned with the side for the block uppermost, flexed partially at the hip and knee joints. The iliac area will be sterilized using povidone-iodine and alcohol, and then drapes will be put on the patient's thigh, with the operator on the right-hand side for blocks on both sides and vice versa for a lefthanded operator. The ultrasound machine will be placed on the opposite side so that the operator's line of sight, the needle, and the screen is in a straight line. A curvilinear low-frequency (3-9 MHz) probe will be used to do a scan of the sub-gluteal region below a line from the ischial tuberosity and greater trochanter which are seen as two hyperechoic bony prominences; the gluteus maximus muscle is as the most superficial muscular layer bridging the two osseous structures; sciatic nerve lies deep into the gluteus maximus muscle and superficial to the quadratus femoris muscle as an oval or roughly triangular hyperechoic structure. A volume of 25 ml of bupivacaine will be injected to perform the block.

The onset and duration of sensory loss and motor blockade will be studied. The loss of pinprick sensation will be checked every 5 minutes till the onset of loss of sensation and then every 2 hours till the regain of sensation. The motor blockade will be assessed every 5 minutes till the loss of movements and then every 2 hours till the regain of movements.