The research was terminated because the recruitment of the study subjects was not smooth and the overseas training of the investigator was scheduled.

Patients undergoing lower extremity surgery with spinal anesthesia are often sedated to reduce patient discomfort due to large noises during surgery and also to reduce anxiety. Most commonly used sedatives include propofol and midazolam, but these agents are known to often cause hypotension or respiratory depression. Dexmedetomidine is a selective alpha 2 adrenergic drug, which acts as a sedative and also has analgesia effects. In contrast to propofol or midazolam, dexmedetomidine rarely causes respiratory depression, and therefore is often used in critically ill patients in the ICU and also in patients undergoing simple procedures. Hemodynamically, dexmedetomidine evokes a biphasic blood pressure response with a short hypertensive phase and subsequent hypotension. Bradycardia is also observed in many patients, which may lead to more serious outcomes when progressing to sinus pause or shock. Therefore, drugs to prevent bradycardia during dexmedetomidine infusion may help patients maintain a more stable hemodynamic state. The present study aims to compare the ability of atropine and glycopyrrolate to prevent bradycardia during dexmedetomidine infusion in patients undergoing lower extremity orthopedic surgery with spinal anesthesia.

Inclusion Criteria:

1. Patients 65 years or older undergoing total knee replacement surgery under spinal anesthesia.
2. ASA class 1-3

Exclusion Criteria:

1. Patients with coagulation abnormalities
2. End organ diseases of liver, lung or kidney
3. Severe aortic stenosis
4. High degree AV block
5. Heart failure
6. Patients on MAO inhibitors
7. History of seizures or epilepsy
8. Glaucoma