Shivering increases the cardiac and systemic energy expenditure, oxygen consumption and carbon dioxide production. Definitive prevention and treatment of shivering is necessary to decrease the related complications and increase post-anesthetic comfort.

Dexmedetomidine a highly selective α2 adrenergic agonist used effectively as a safe analgesic via different routes and mechanisms, including intravenous (i.v.), neuraxial and perineural routes. Dexmedetomidine has been used for prevent shivering but, the results of its efficacy is still controversy.

No studies to date have investigated the best administration route of dexmedetomidine to dominantly prevent the occurrence of shivering after spinal anesthesia or associated with the least grade.

This prospective, randomized, double blinded study was designed to investigate the best administrative route of dexmedetomidine firstly, as a preventive of neuraxial shivering and secondly as adjunctive analgesic.

The incidence of post-spinal anesthesia shivering was the primary outcome. Perioperative hemodynamics, postoperative pain scores during rest and at 45-degree flexion of the knee, the analgesic duration, the first postoperative day analgesic consumption, the sedation score and early ambulation ability were the secondary outcomes.

Inclusion Criteria:

• adult patients
• both genders
• American Society of Anesthesiologists physical status I and II
• scheduled for unilateral primary TKA under spinal anesthesia

Exclusion Criteria:

• chronic opioid use
• known allergy to the used drugs
• any contraindications to regional anesthesia like; patient refusal, coagulopathy, neuropathy or infection at the injection site

The study anesthetic drugs both for adductor-canal-blockade and for intravenous infusion were prepared according to the group by an anesthetist who was not involved in its injection or the perioperative assessment