Inclusion Criteria- age 18-45;
- receiving spinal anesthesia or combined spinal and epidural anesthesia to undergo cesarean section
Exclusion Criteria- Patients who have major cardiovascular disease,preexisting of hypertension or gestational hypertension, preeclampsia and body mass index greater than 35kg/m2;
- Patients who have skin lesion at the place where the electrode is supposed to be applied;
- Emergency cesarean section patients.