The purpose of this trial is to determine the effective volume of hydroxyethylstarch 130/0.4 which would prevent the occurence of maternal hypotension in 50% of healthy pregnant women undergoing a cesarean section under spinal anesthesia.

The incidence of spinal anesthesia-induced hypotension in pregnant women undergoing a cesarean section is high. A preoperative fluid bolus of undetermined volume is frequently administered to lower the incidence of maternal hypotension, with a somewhat poor efficacy. Recently, several investigations have shown that the use of a phenylephrine infusion after the induction of spinal anesthesia results in a significant reduction in hypotensive episodes. Given the high efficacy of this therapy (incidence of hypotension around 20%), it is possible to determine the effective volume of fluid which would prevent hypotension in 50% of the patients studied (ED50).

Healthy term pregnant women undergoing elective cesarean section under spinal anesthesia will be recruited in this trial. The spinal anesthesia regimen will be standardized and all subjects will receive a phenylephrine infusion. The fluid investigated is hydroxyethylstarch (HES) 130/0.4 (Volulyte(R)). The ED50 will be determined using an up-down sequential allocation method initially described by Dixon & Massey. The determination of the HES ED50 will help the anesthesiologist in further treating maternal hypotension appropriately.

Inclusion Criteria:

• Healthy pregnant women (ASA I or II)
• Normal pregnancy
• Term gestation (37 weeks and above)
• Elective cesarean section
• Spinal anesthesia

Exclusion Criteria:

• Cardiopathies
• Hypertensive disease/ pre-eclampsia / eclampsia
• Any contraindication to neuraxial anesthesia
• Patient refusal
• Body mass index > 30 at first antenatal visit and > 32 at cesarean section
• Twin pregnancy
• Known allergies to HES
• Emergency cesarean section