Maternal hypotension during spinal anaesthesia for Caesarean delivery may bring various adverse effects. It is therefore important to closely monitor hypotension during spinal anaesthesia, however current technology does not allow the blood pressure monitoring to respond in timely manner should there be any occurrence of hypotension. The investigators developed an advanced double-intravenous vasopressor automated system (ADIVA) so as to tackle this issue via novel algorithm to control blood pressure more rigorously with more stable haemodynamic profiles.

The incidence of maternal hypotension during spinal anaesthesia for Caesarean delivery is reported to be as high as 70-90%. The potential adverse effects resulting from maternal hypotension are nausea, vomiting, cardiac dysfunction, foetal acidosis and hypoxia.

Hypotension during spinal anaesthesia is currently detected using an intermittent blood pressure (BP) monitor cycling and reactive administration of vasopressors upon detection. The use of conventional non-invasive BP monitoring is limited by the time required to inflate and to deflate the cuffs commonly applied to the arm, which subsequently leads to a failure to react in a timely manner to BP changes when they occur.

The DIVA system (double-intravenous vasopressor automated system) previously developed helped tackle the limitations associated with the conventional management of hypotension in Caesarean sections under spinal anaesthesia. In a recent randomized controlled trial the DIVA system achieved less incidence of maternal hypotension compared to conventional management, however the side effects in mother and baby were still not fully eliminated.

In this proposed study a new algorithm for an advanced DIVA (ADIVA) system will be developed to control BP more rigorously by detecting BP with more stable haemodynamic profiles and thereby improve patient outcomes. The clinical trial will be conducted in 2 phases. The first phase included the use of ADIVA in 76 subjects who undergo spinal anaesthesia for Caesarean delivery to test its safety and efficacy. The second phase was a randomised controlled trial to investigate the use of ADIVA in comparison to the existing DIVA system in 97 patients undergoing spinal anaesthesia for Caesarean section.

Inclusion Criteria:

• Healthy adult (American Society of Anesthesiologists physical status 1 and 2) parturients;
• With singleton full-term pregnancy;
• The indication for an elective cesarean delivery;
• The use of spinal anaesthesia for cesarean delivery;
• Anthropometric profile within the following range: age 21-50 years old, weight 40-90 kg and height of 145-170 cm.

Exclusion Criteria:

• Obstetric (e.g. pre-eclampsia, premature rupture of amniotic membranes for more than 48 hours, gestational diabetes on insulin, pregnancy-induced hypertension on medication) and uncontrolled medical (e.g. cardiac disease) complications;
• Contraindication to spinal anaesthesia and/or allergy to opioids.

Only female patients undergoing cesarean delivery will be recruited.