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

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Hypotension is a very common complication of spinal anesthesia for cesarean delivery, and can have unwanted side effects on both mother and fetus if not treated promptly. Phenylephrine has been the drug of choice to treat this spinal-induced hypotension. Although phenylephrine is safe to use for this indication, it has been associated with reflex bradycardia and a reduction in cardiac output. 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. The investigators recently conducted a study to determine the ED90 of norepinephrine, and now plan to compare bolus doses of phenylephrine to norepinephrine for treating hypotension following spinal anesthesia for cesarean section. The investigators hypothesize that norepinephrine, when given as a bolus to prevent post spinal hypotension, will result in around 70% relative decrease in the rate of bradycardia when compared to phenylephrine in patients undergoing elective cesarean delivery under spinal anesthesia.
Accepts Healthy Volunteers?
Accepts Healthy Volunteers
Lead Sponsor:
Samuel Lunenfeld Research Institute, Mount Sinai Hospital
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