The purpose of this study is to investigate the preventive effect of norepinephrine on post-spinal hypotension and the effect of norepinephrine on inferior vena cava collapsibility index (IVC-CI).

Post-spinal hypotension is a frequent complication during spinal anesthesia for cesarean delivery. It affects nearly 50-60% of patients without appropriately treat. Vasopressors has been highly recommended for routine prevention and/or treatment of post-spinal hypotension. Norepinephrine is new vasopressor that has been suggested as a potential alternative to phenylephrine and was recently introduced in obstetric anesthesia because of the minimal cardiac depressant effect. The purpose of this study is to investigate the preventive effect of norepinephrine on post-spinal hypotension and the effect on inferior vena cava collapsibility index (IVC-CI).

Inclusion Criteria:

• 18-45 years
• American Society of Anesthesiologists physical status classification I to II
• Scheduled for elective cesarean delivery under spinal anesthesia
• Full-term, singleton, pregnant women

Exclusion Criteria:

• Height of no more than 150 centimeters
• Body weight greater than 100 kg or BMI greater than 30
• Labor analgesia had been performed
• Contraindication of spinal or epidural anesthesia
• Eclampsia or chronic hypertension or baseline blood pressure ≥160mmHg
• Hemoglobin <7g/dl
• Fetal distress or known abnormal fetal development
• Severe vascular disease
• Diabetes mellitus or cardiovascular disease or nervous system disease