Inclusion Criteria:  Aged 18-65 years old American Society of Anesthesiologist (ASA) physical status I or II Planning for spinal anesthesia  Exclusion Criteria:  History of allergy to the drugs used in the study Pregnant patients With neuromuscular disease, hyperthyroid, severe cardiopulmonary diseases, liver and/or renal disorders Used drugs that could interact with MgSO4 such as nifedipine Preoperative body temperature less than 36oC or more than 37.5oC