ED90 of Norepinephrine and Phenylephrine Boluses Under Intensive Treatment in Preeclamptic Patients

Inclusion Criteria: * 18-45 years * Primipara or multipara * Singleton pregnancy ≥32 weeks * American Society of Anesthesiologists physical status classification I to III * Scheduled for cesarean section under spinal anesthesia Exclusion Criteria: * Baseline blood pressure ≥160 mmHg * Body height \< 150 cm * Body weight \> 100 kg or body mass index (BMI) ≥ 40 kg/m2 * Eclampsia or chronic hypertension * Hemoglobin \< 7g/dl * Fetal distress, or known fetal developmental anomaly