Shivering is a common post-anesthetic complication occurring in up to 65% of patients undergoing spinal or epidural anesthesia. Shivering may interfere with electrocardiogram, blood pressure and oxygen saturation monitoring. In addition, shivering increases oxygen consumption, carbon dioxide production and metabolic rate by up to 400%. Thus, it may result in problems in patients with low cardiac and pulmonary reserves. Preventing shivering could therefore result in better postoperative outcomes or reduce the incidence of post-surgical complications.

Magnesium sulfate (MgSO4) has anti-shivering effects. Moreover, it has potential neuroprotective effects and may enhance neuroprotection against the effects of hypothermia. Intrathecal MgSO4 administration provides effective perioperative analgesia and can prolong the period of anesthesia and sensory blockade without any additional side-effects. However, most of the research on the role of MgSO4 in the prevention of shivering has focused on intravenous infusion of this drug. Few clinical trials have examined the effect of adding intrathecal MgSO4 to anesthetic agents such as bupivacaine to suppress anesthesia-related shivering in patients. Similar to infusion studies, we hypothesized that the addition of intrathecal injection of MgSO4 to bupivacaine would improve perioperative shivering in female patients undergoing elective caesarean section. Few previous studies evaluated neuroaxial anti-shivering effects of intrathecal magnesium and none evaluated the anti-shivering effect of intrathecal MgSO4. Therefore, we elected to use the lowest dosage (25 mg MgSO4) that was formerly utilized for investigation of analgesic effects.

Magnesium sulphate is an intracellular cation with various physiologic functions such as enzyme activation, nerve signal conduction, protein synthesis and vasomotor tonicity regulation. Magnesium sulphate has been used in various clinical situations including preeclampsia, tocolysis, arrhythmias, myocardial ischemia, bronchial asthma and postoperative shivering.

Inclusion Criteria:

1. Age 18 to 35years.
2. Undergo elective cesarean section under spinal anesthesia.
3. ASA physical status I-II.
4. Singleton pregnancy.
5. At least 38 weeks gestation.

Exclusion Criteria:

1. Women with history of cardiac, liver or kidney diseases.
2. Women with allergy to amide local anesthetics or medication included in the study.
3. Women with any neurological problem.
4. Any contraindication of regional anesthesia.
5. Failed or insatisfactory spinal block.
6. Preoperative temperature more than 38⁰ C.