Midodrine for Improving Hemodynamics After Spinal Anesthesia

Patients will receive oral 10 mg tablet of midodrine with small sips of water one hour before arrival in the operation room. All patients will be monitored in with noninvasive blood pressure as well as continuous electrocardiogram (ECG) and pulse oximetry (SpO2). Before placement of spinal anesthesia, all patients will receive an IV bolus of 10mL/kg of Lactated Ringer's . Spinal anesthesia (midline puncture) will be performed in sitting position by a staff anesthetist at L3-L4 or L4-L5 with a 25-gauge Withacre needle injecting 12.5 mg of hyperbaric 0.5% bupivacaine (2.5 mL) with 10μg fentanyl. After injection,the patients will be turned supine.

: Patients will receive Inert tablet containing sugar (placebo) with small sips of water one hour before arrival in the operation room. All patients will be monitored in with noninvasive blood pressure as well as continuous electrocardiogram (ECG) and pulse oximetry (SpO2). Before placement of spinal anesthesia, all patients will receive an IV bolus of 10mL/kg of Lactated Ringer's . Spinal anesthesia (midline puncture) will be performed in sitting position by a staff anesthetist at L3-L4 or L4-L5 with a 25-gauge Withacre needle injecting 12.5 mg of hyperbaric 0.5% bupivacaine (2.5 mL) with 10μg fentanyl. After injection,the patients will be turned supine