A Comparative Study Between Neostigmine and Dexamethasone as an Adjuvant to Bupivacaine in Adductor Canal Block After Knee Arthroscopy Surgery

90 participants in this study will be randomized into three groups based on computer generated numbers using computerized generated random tables. The patients enrolled in the study will be transferred to the operation room and monitored all through the surgical procedure using pulse oximeter, non-invasive blood pressure and ECG.

To perform spinal anesthesia ,the patient will be positioned in the sitting position then sterilization of the back using betadine solution 5% will be done then the iliac crest will be identified and the opposite intervertebral space(L4-L5) will be marked then 5 ml of lidocaine 2% will be infiltrated in the skin and subcutaneous tissue then a spinal needle (25G) will be introduced to the intrathecal space and after ensuring that clear cere¬brospinal fluid will be in free flow injection of 15-20mg of bupivacaine 0.5% and 25mcg of fentanyl will be administrated then the patient will be positioned in the supine position.

If hypotension, (decrease in the mean arterial blood pressure of more than 20%from base line) occurs, 9mg intravenous ephedrine will be given with 200ml bolus crystalloids. If bradycardia (heart rate below 50beat / minute) occurs, 0.5mg intravenous atropine will be given. After the surgical procedure the patients will be randomly allocated using computerized generated random tables in to three equal groups and the random numbers will be concealed in closed opaque envelopes which will be kept by the senior anesthesia staff, the three groups are:

• Group neostigmine: The patients in this group will be administered 500 mcg neostigmine (1 ml) + 1 ml isotonic saline (22) as adjuvant to 20 ml bupivacaine 0.50 % in the adductor canal block.
• Group dexamethasone: The patients in this group will be administered 8 mg dexamethasone (2 ml) (23) as adjuvant to 20 ml bupivacaine 0.50 % in the adductor canal block.
• Group control: The patients in this group will be administered 2 ml isotonic saline + 20 ml bupivacaine 0.50 % in the adductor canal block (control group).

With the patient in the supine position, the procedural needle (Braun Stimuplex Ultra Insuflated Echogenic Needle 22G) will be inserted in plane from the anteromedial side at the mid thigh level. It will be advanced through the sartorius muscle and fascia under ultrasound guidance, using a Siemens Acuson X300 ultrasound equipped with a linear transducer after sterilization of the skin with betadine solution 5%, and the adductor canal, with the superficial femoral artery and vein within, will be identified. Once the needle tip will be located in the adductor canal, the anaesthetic solution will be injected anterior to the artery and deep into the sartorius muscle (24) then patient will be transferred to the PACU then to the ward.