Minimum Effective Volume of Crystalloid Co-Loading to Prevent Spinal Anesthesia-Induced Hypotension in Cesarean Section

Determination of the Minimum Effective Volume of Crystalloid Co-Loading for Preventing Spinal Anesthesia-Induced Hypotension in Cesarean Section: A Biased Coin Design Study

The goal of this clinical trial is to find the minimum effective volume of IV crystalloid that should be given with phenylephrine to prevent hypotension caused by spinal anesthesia in healthy, term pregnant adults having elective cesarean delivery.

The main questions are:

What is the minimum effective volume (MEV90, mL/kg) of crystalloid co-loading that prevents spinal-anesthesia-induced hypotension in ≥90% of participants?

What maternal side effects and newborn outcomes occur with this strategy (e.g., nausea/vomiting, need for extra vasopressors, total fluids/blood loss, Apgar scores, and umbilical cord blood gases)?

There is no separate comparison group; this is a single-arm, adaptive dose-finding study.

Participants will:

Receive a predefined volume of IV crystalloid over ~10 minutes during spinal anesthesia while phenylephrine is infused. Have blood pressure and symptoms monitored; receive rescue treatment if needed. Allow the next participant's fluid volume to be adjusted based on whether hypotension occurred (biased-coin design). Be followed through postoperative day 2 for maternal and newborn outcomes.

Inclusion Criteria:

• Pregnant adults ≥19 years scheduled for elective cesarean delivery under spinal anesthesia
• Term pregnancy (≥37 weeks' gestation)

Exclusion Criteria:

• Emergency cesarean delivery
• Hypertensive disorders of pregnancy (preeclampsia/eclampsia) or hypertension
• Multiple gestation
• Body weight <50 kg or BMI >35 kg/m²
• Renal impairment or eGFR ≤90 mL/min/1.73 m²
• Heart failure or other heart disease
• History of bronchial asthma or other pulmonary disease