Hypotension occurs commonly during spinal anaesthesia for caesarean section with maternal and fetal adverse effects. The investigators developed a double-vasopressor automated system incorporating continuous non-invasive haemodynamic monitoring using NexfinTM with a two-step algorithm.

Hypotension occurs commonly during spinal anaesthesia for caesarean section with maternal and fetal adverse effects. We developed a double-vasopressor automated system incorporating continuous non-invasive haemodynamic monitoring using Nexfin cardiac output monitor with a two-step algorithm. The system delivered phenylephrine 25 mcg or ephedrine 2 mg (if heart rate<60 beats.min-1) every 30 seconds when systolic blood pressure was between 90-100% of baseline. The system delivered phenylephrine 50 mcg or ephedrine 4 mg (if heart rate<60 beats.min-1) every 30 seconds when systolic blood pressure was <90% of baseline.

A randomised controlled trial will be done to compare with manual bolus technique. With the manual bolus technique, phenylephrine 50mcg or ephedrine 4mg (if heart rate<60 beats.min-1) every 60 seconds when systolic blood pressure was between 90-100% of baseline. The system delivered phenylephrine 100mcg or ephedrine 8mg (if heart rate<60 beats.min-1) every 60 seconds when systolic blood pressure was <90% of baseline.

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