This study aims to find out if preoperatively given dexmedetomidine is effective analgesic adjuvant for treating postoperative pain in patients undergoing elective total knee arthroplasty (TKA). Another aim is to determine if premedication with intranasal dexmedetomidine could provide sufficient sedation to alleviate anxiety during TKA.

Patients undergoing total knee arthroplasty (TKA) under spinal anesthesia often request sedation to alleviate anxiety. Dexmedetomidine may be ideally suited to provide sedation during surgery as it offers sedation and analgesia without causing significant respiratory depression. Furthermore, dexmedetomidine has beneficial synergistic interactions with opioids and sedative drugs.

Altogether 80 patients scheduled for elective unilateral TKA under spinal anesthesia will be included in the prospective, randomized and controlled parallel-group study. Patients will be randomized into two groups, forty patients in each group. All patients will receive preoperatively 1000 mg of oral paracetamol as premedication. One group receives a single bolus dose of intranasal 1 ug/kg dexmedetomidine (DEX group) and the other group receives euvolemic dose (10 µL/kg) of saline (PLACEBO-group).

Spinal anesthesia will be performed using bupivacaine (5 mg/mL) using 2.0-2.5 mL dose, the amount depending on the clinical judgement of the anesthesiologist responsible for the patient. If patient needs additional analgesic after spinal anesthesia, 50 µg dose of intravenous fentanyl or 3-5 mg of intravenous midazolam may be administered intraoperatively.

Postoperative pain management in the surgical ward includes oral paracetamol 1000 mg every 8 hours, and from the first postoperative day onwards patients receive oral naproxen/esomeprazole 500/20 mg twice a day. Oral oxycodone (5-10 mg) will be used, if the pain (measured with numerical rating scale, NRS, min 0, max 100, higher scores mean worse outcome) is moderate or intense (NRS>30) after paracetamol and naproxen.

Postoperative pain (NRS) and opioid consumption (mg) will be measured and analysed together with intraoperative sedative used (mg, midazolam and/or fentanyl allowed).

Inclusion Criteria:

1. The patient is scheduled for elective unilateral total knee arthroplasty (TKA) under spinal anesthesia
2. Fluent skills in finnish language (to understand the given information and to be able to give informed consent and communicate with the study personnel)
3. Age between 35 and 80 years
4. Weight between 50 and 100 kg
5. American Society of Anesthesiologists status 1-3
6. Written informed consent from the patient

Exclusion Criteria:

1. A previous history of intolerance to the study drug or related compounds and additives
2. Disease or condition affecting patient's ability to give written informed consent
3. Existing or recent disease possible affecting absorption, distribution, metabolism, excretion or response to the study drug
4. History of severe cardiac disease (valvular insufficiency, severe left ventricular dysfunction) or abnormal ECG rhythm (bradycardia < 50/min, 2nd or 3rd degree atrioventricular-block, pacemaker)
5. Preoperative systolic blood pressure <110 mmHg
6. Chronic use of strong opioids, pregabalin, gabapentin, amitriptyline or duloxetine
7. Participation in any other study concomitantly or within one month prior to the entry into this study
8. Clinically significant abnormal findings in physical examination or laboratory screening
9. Pregnancy or breastfeeding
10. Use of any drugs known to cause enzyme induction or inhibition for a period of 30 days prior to the study, use of any natural products (including grapefruit products) for at least 14 days prior to the study and caffeine containing products for at least 24 hours prior to the study. The use of regular doses of paracetamol is allowed.