Single Bolus Intravenous Ephedrine Attenuates Reduction of Core Body Temperature in Patients Undergoing Spinal Anesthesia for Arthroscopic Knee and Ankle Surgery

Inclusion Criteria: * Patient undergoing knee or ankle arthroscopic surgery under spinal block at department of orthopaedic Ramathibodi Hospital * BMI 17-30 kg/m2 * ASA physical status 1-3 * Age 18-70 * Last oral intake more than 6 hours (2 hours for water) * Consent form acquired Exclusion Criteria: * Patient who are contraindicated for spinal block * Anesthesia level higher than T4 or lower than T10 * Tympanic temperature more than 37.5 or less than 35.5 degrees Celsius * Otitis or other ear infection * Patients who receive alpha adrenergic blocker or beta adrenergic blocker * Initial blood pressure presenting in operating theater 140 90 mmHg repeat after rest 5 minutes * Patient refusal