This study compared the effects of prophylactic infusion of metaraminol, phenylephrine and norepinephrine adjusted according to body weight on fetal acid-base balance and maternal hemodynamics.

At present, the ED90 of metaraminol, phenylephrine, and norepinephrine in the prevention of cesarean section hypotension has been explored. We compare the effects of three drugs on the fetus and mothers at the concentration of ED90 to provide advice on the use of vasoactive drugs for obstetrics anesthesia .

Inclusion Criteria:

1. Singleton pregnancy at term scheduled to be delivered via elective cesarean delivery;
2. height 150-180 cm;
3. American Society of Anesthesiologists (ASA) physical status II-III;
4. body mass index (BMI) <35 kg/m2.

Exclusion Criteria:

1. transverse presentation, fetal macrosomia;
2. uterine abnormalities (eg, large fibroids, bicornuate uterus);
3. polyhydramnios;
4. ruptured membranes, oligohydramnios;
5. intrauterine growth restriction;
6. gestational or nongestational hypertension, diabetes, or eclampsia;
7. hypertensive disorders or any condition associated with autonomic neuropathy (such as diabetes mellitus for >10 years) or renal failure;
8. contraindications for combined spinal-epidural anesthesia;
9. participants who declined to sign informed consent forms.