Analgesic Effect of Ropivacaine Combined With Hydromorphone for CSEA After Total Knee Arthroplasty

Inclusion Criteria: * Age between 55 and 80 years old. * ASA grade I to III. * BMI:20-29kg/m2. * No recent use of sedatives, opioids, or other analgesics. * There was no contraindication of spinal anesthesia, severe dysfunction of heart, lung and other important organs or serious systemic diseases. * Patients were willing to participate in the study and signed the informed consent. Exclusion Criteria: * The patient has mental illness or cannot cooperate with the completion of spinal anesthesia. * The patient had a history of spinal surgery and spinal deformity. * Patients had a history of opioid intolerance or adverse reactions. * puncture site infection, coagulopathy or recent use of anticoagulant drugs. * History of allergy to local anesthetics. * Failed puncture. * Unable to cooperate to complete the research process.