Hypotension occurs commonly during spinal anesthesia for caesarean section with maternal and fetal adverse effects. The investigators developed a double-vasopressor automated system incorporating continuous non-invasive arterial pressure monitoring (CNAP, CNSystems, Austria).

Hypotension occurs commonly during spinal anesthesia for cesarean section with maternal and fetal adverse effects. The investigators developed a double-vasopressor automated system incorporating continuous non-invasive arterial pressure (CNAP, CNSystems, Austria) monitoring feeding hemodynamic data to a laptop computer, which triggers syringe pumps to deliver phenylephrine 50mcg or ephedrine 4mg (if heart rate<60 beats.min-1) every 30 seconds when systolic blood pressure fell to below 90% of baseline.

A randomised controlled trial was done to compare with manual bolus technique. With the manual bolus technique, phenylephrine 100mcg or ephedrine 8mg (if heart rate<60 beats.min-1) was given every 60 seconds by the attending anesthesiologist when systolic blood pressure was below 90% of baseline as measured by conventional intermittent non-invasive blood pressure monitoring.

Inclusion Criteria:

• age 21-45 years old,
• weight 40-90 kg,
• height 145-170 cm

Exclusion Criteria:

• contraindications to spinal anaesthesia,
• allergy to drugs used in the study, and
• those with uncontrolled medical conditions such as hypertension, diabetes mellitus, and cardiovascular disease

Study participants need to be pregnant and undergoing elective cesarean section