A study comparing dexamethasone and dexmedetomidine added to ropivacaine given for the pain relief block for the patients undergoing total knee replacement surgery

INTERVENTION: Intervention1: Ropivacaine and Dexmedetomidine: Ultrasound‐guided adductor canal block with 20 mL of 0.2% ropivacaine plus dexmedetomidine 0.5 g/kg (diluted to a total volume of 22 mL) single time administered and observed postoperatively for 24 hours Control Intervention1: Ropivacaine and dexamethasone: Ultrasound‐guided adductor canal block with 20 mL of 0.2% ropivacaine plus dexamethasone 4 mg (diluted to a total volume of 22 mL) single time administered and observed postoperatively for 24 hours CONDITION: Health Condition 1: M171‐ Unilateral primary osteoarthritisof knee PRIMARY OUTCOME: Duration of postoperative analgesia, defined as the time from completion of the ultrasound‐guided adductor canal block to the first request for rescue analgesia.Timepoint: Within the first 24 hours after surgery. SECONDARY OUTCOME: VAS scores on rest and movement. Total opioid consumption and adverse events anyTimepoint: Within 24 hours after surgery INCLUSION CRITERIA: Patients who are willing to give informed consent and belongs to ASA 1 or 2