During Cesarean delivery, phenylephrine is used to maintain the patient's blood pressure. Low blood pressure is the most common side effect of the spinal medication used to anesthetize the patient prior to the start of surgery. This low blood pressure can also trigger unpleasant side effects such as nausea, vomiting and low Apgar scores for the baby.

Currently there are 2 methods of phenylephrine administration during Cesarean section. One method is by intermittent bolus and the other is by continuous infusion. It is ideal to have a regimen for phenylephrine administration that maintains blood pressure without compromising cardiac output.

In this study, cardiac output and blood pressure will be measured by transthoracic bioimpedance, which is a new technique of noninvasive continuous cardiac output monitoring.

The hypothesis of this study is that the continuous infusion of phenylephrine will be equally effective in maintaining blood pressure as compared to the intermittent injection, and will induce less hemodynamic changes.

Inclusion Criteria:

• Ability to communicate in English
• Elective Cesarean Delivery under spinal anesthesia
• Normal singleton pregnancy beyond 36 weeks gestation
• ASA physical status I/II
• Weight 50-100 kg, height 150-180 cm
• Age over 18 years

Exclusion Criteria:

• Patient refusal
• Inability to communicate in English
• Allergy or hypersensitivity to phenylephrine
• Preexisting or pregnancy-induced hypertension
• Cardiovascular or cerebrovascular disease
• Fetal abnormalities
• History of diabetes, excluding gestational diabetes
• Contra-indications for spinal anesthesia