BACKGROUND: One previous study has confirmed that the marginally hyperbaric solutions of
bupivacaine can maintain good quality of anesthesia and get a more steadily hemodynamic
status than commonly hyperbaric solutions, some authors confirmed the plain ropivacaine for
cesarean section have a higher failure rate and commonly hyperbaric solutions of ropivacaine
have a higher incidence of side reaction. It is unclear what the efficacy of spinal
marginally hyperbaric ropivacaine for elective cesarean delivery.We hypothesized that the
marginally hyperbaric ropivacaine will get a similar efficacy to commonly hyperbaric
solutions but a more steadily hemodynamic status.

OBJECTIVE In this prospective, randomized, double-blinded study, Investigator will compare
the clinical efficacy and adverse effect of spinal anesthesia with commonly hyperbaric and
marginally hyperbaric ropivacaine for elective cesarean delivery.

Main outcome measures: The maximum cephalad sensory block level; the change of continuous
cerebral oxygen desaturation (ScO2) over time; the incidence of hypotension and nausea and
vomiting; the change of invasive arterial pressure; the consumption of ephedrine; the
incidence of shivering; the onset time to T8 dermatome; the quality of anesthesia (efficacy
of motor block and sensory block)