A Comparison of Intermittent Intravenous Boluses of Phenylephrine and Norepinephrine to Prevent Spinal-induced Hypotension in Cesarean Deliveries

Norepinephrine is a potent vasopressor used to treat hypotension in the critical care setting. Recent studies have looked at norepinephrine's use in the obstetric setting, and have shown that it can be used safely and also has favourable hemodynamic properties when compared to phenylephrine, with less bradycardia and less depression of cardiac output. These studies have been limited to using norepinephrine as an infusion and there is limited data with it being used as a bolus to prevent hypotension. A recent study was undertaken at Mount Sinai hospital to determine the ED90 of norepinephrine to treat post spinal hypotension. Secondary outcome data from this trial showed that the incidence of bradycardia associated with this treatment is approximately 7.5%, several times less when compared to the reported 30% with phenylephrine. It would therefore be prudent at this stage to undertake a randomized trial comparing the hemodynamic profile of phenylephrine (our standard practice) and norepinephrine used as intermittent boluses to prevent hypotension and avoid decrease in heart rate during cesarean delivery.

Inclusion criteria

• Informed consent
• Elective CS under spinal anesthesia
• Normal singleton pregnancy beyond 36 weeks gestation
• ASA physical status 2-3
• Current (pregnant) 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
• Allergy or hypersensitivity to sulfite
• Use of monoamine oxidase inhibitors, triptyline or imipramine antidepressants
• Untreated hyperthyroid patients