The purpose of this study is to investigate the potency between prophylactic norepinephrine and phenylephrine boluses for postspinal anesthesia hypotension in patients undergoing caesarean section.

Post-spinal anesthesia hypotension is a frequent complication during spinal anesthesia for cesarean section. The incidence of post-spinal anesthesia hypotension is as high as 62.1-89.7% if prophylactic measures are not taken. Vasopressor has been highly recommended for routine prevention and/or treatment of post-spinal anesthesia hypotension. As a potential substitute drug for phenylephrine, norepinephrine has gradually been used in parturients undergoing cesarean section. There's some evidence that prophylactic infusion of norepinephrine could effectively reduce the incidence of post-spinal anesthesia hypotension in parturients undergoing cesarean section. However, few studies had been indicated the ED50 (prevent postspinal hypotension in 50% of patients) and ED90 of prophylactic norepinephrine bolus and its potency compared to phenylephrine for postspinal anesthesia hypotension in patients undergoing caesarean section. The purpose of this study is to investigate the potency between prophylactic norepinephrine and phenylephrine boluses for postspinal anesthesia hypotension in patients undergoing caesarean section.

Inclusion Criteria:

• 18-45 years
• Primipara or multipara
• Singleton pregnancy ≥37 weeks
• American Society of Anesthesiologists physical status classification I to II
• Scheduled for cesarean section under spinal anesthesia

Exclusion Criteria:

• Body height < 150 cm
• Body weight > 100 kg or body mass index (BMI) ≥ 40 kg/m2
• Eclampsia or chronic hypertension or baseline blood pressure ≥180 mmHg
• Hemoglobin < 7g/dl
• Fetal distress, or known fetal developmental anomaly