Newly Published
Perioperative Medicine  |   September 2017
A Random-allocation Graded Dose–Response Study of Norepinephrine and Phenylephrine for Treating Hypotension during Spinal Anesthesia for Cesarean Delivery
Warwick D. Ngan Kee, M.D., F.A.N.Z.C.A., F.H.K.A.M.
Author Notes
  • From the Department of Anaesthesia and Intensive Care, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong, China.
  • Submitted for publication March 9, 2017. Accepted for publication August 10, 2017.
    Submitted for publication March 9, 2017. Accepted for publication August 10, 2017.×
  • Acknowledgments: The author thanks Floria F. Ng, R.N., B.A.Sc., research nurse, Department of Anesthesia and Intensive Care, The Chinese University of Hong Kong (Shatin, Hong Kong, China), for her assistance with recruiting patients and preparing study drugs.
    Acknowledgments: The author thanks Floria F. Ng, R.N., B.A.Sc., research nurse, Department of Anesthesia and Intensive Care, The Chinese University of Hong Kong (Shatin, Hong Kong, China), for her assistance with recruiting patients and preparing study drugs.×
  • Research Support: Supported by the Department of Anesthesia and Intensive Care, The Chinese University of Hong Kong (Shatin, Hong Kong, China).
    Research Support: Supported by the Department of Anesthesia and Intensive Care, The Chinese University of Hong Kong (Shatin, Hong Kong, China).×
  • Competing Interests: The author declares no competing interests.
    Competing Interests: The author declares no competing interests.×
  • Reproducible Science: Full protocol available at: wngankee@gmail.com. Raw data available at: wngankee@gmail.com.
    Reproducible Science: Full protocol available at: wngankee@gmail.com. Raw data available at: wngankee@gmail.com.×
  • Correspondence: Address correspondence to Dr. Ngan Kee: Department of Anesthesiology, Sidra Medical and Research Center, P.O. Box 26999, Doha, Qatar.wngankee@gmail.com. Information on purchasing reprints may be found at www.anesthesiology.org or on the masthead page at the beginning of this issue. Anesthesiology’s articles are made freely accessible to all readers, for personal use only, 6 months from the cover date of the issue.
Article Information
Perioperative Medicine / Cardiovascular Anesthesia / Obstetric Anesthesia / Regional Anesthesia
Perioperative Medicine   |   September 2017
A Random-allocation Graded Dose–Response Study of Norepinephrine and Phenylephrine for Treating Hypotension during Spinal Anesthesia for Cesarean Delivery
Anesthesiology Newly Published on September 7, 2017. doi:10.1097/ALN.0000000000001880
Anesthesiology Newly Published on September 7, 2017. doi:10.1097/ALN.0000000000001880
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Abstract

Background: Norepinephrine has been investigated as a potential alterative to phenylephrine for maintaining blood pressure during spinal anesthesia for cesarean delivery with the advantage of less depression of maternal heart rate and cardiac output. However, the relative potencies of these two vasopressors have not been fully determined in this context.

Methods: In a random-allocation, graded dose–response study, 180 healthy patients undergoing spinal anesthesia for elective cesarean delivery received a single bolus of norepinephrine in one of six different doses ranging from 4 to 12 µg or phenylephrine in one of six different doses ranging from 60 to 200 µg to treat the first episode of hypotension. The magnitude of response was measured as the percentage of full restoration of systolic blood pressure to the baseline value. Dose–response analysis was performed using nonlinear regression to derive four-parameter logistic dose–response curves, which were compared to determine relative potency.

Results: Data were analyzed for 180 patients. The estimated ED50 values (dose giving a 50% response) were norepinephrine 10 µg (95% CI, 6 to 17 µg) and phenylephrine 137 µg (95% CI, 79 to 236 µg). The estimated relative potency ratio for the two drugs was 13.1 µg (95% CI, 10.4 to 15.8 µg).

Conclusions: Comparative dose–response analysis was completed for norepinephrine and phenylephrine given as a bolus to treat the first episode of hypotension in patients undergoing spinal anesthesia for cesarean delivery. The estimated dose equivalent to phenylephrine 100 µg was norepinephrine 8 µg (95% CI, 6 to 10 µg). These results may be useful to inform the design of future comparative studies.