Up-Down Determination of the ED90 of Phenylephrine for Hypotension Prophylaxis in Cesarean Delivery
Condition: Spinal Induced Hypotension in Cesarean Delivery
MeSH terms: Hypotension
Intervention: Phenylephrine infusion
Intervention description: Up-down, biased coin design
Intervention MeSH terms: Phenylephrine; Oxymetazoline
Phase: Phase 4
Study type: Interventional
Primary purpose: Prevention
Intervention model: Single Group Assignment
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Enrollment: 45.0
Sex: Female
Minimum age: 18 Years
Healthy volunteers: Accepts Healthy Volunteers

Summary:

      This study is designed to determine the ED90 for an infusion of phenylephrine to prevent
      spinal induced low blood pressure in parturients presenting for an elective cesarean
      delivery. The up-down methodology (UDM) is commonly used study method to determine the dose
      of a drug that causes the desired effect in over 90% of the subjects to whom it given. For
      example: the investigators want to know what is the best dose of phenylephrine (from a range
      of commonly used doses) to prevent a drop in blood pressure during cesarean delivery ninety
      times out of one hundred when it is given at that dose. The ED90 is the effective dose at
      which 90% of subjects will have a "positive" response to a phenylephrine infusion, i.e. no
      drop in blood pressure. The investigators hypothesize that the ED90 will be between 40 - 60
      mcg/min.

      The primary outcome measure is the ED90 for phenylephrine infusions that prevents a drop in
      blood pressure in women undergoing cesarean delivery.
    

Eligibility criteria:

        Inclusion Criteria:

          1. Non-emergent cesarean delivery with planned spinal anesthesia (i.e. elective planned
             cesarean delivery for malposition, patient choice, cervical pelvic disproportion,
             previous cesarean delivery and other diagnosis that require a predetermined cesarean
             delivery)

          2. American Society of Anesthesia physical status class I & II (ASA I - Healthy, ASA II -
             mild and controlled systemic disease, eg. controlled essential hypertension)

          3. Age ≥ 18 years (Standard within the obstetrical literature)

          4. Term gestational age

          5. English-speaking

        Exclusion Criteria:

          1. Morbid Obesity (Body Mass Index ≥ 45 kg/m2) (Morbidly obese parturients require a dose
             of local anesthetic less than the standardized dose in this study, typically have an
             exaggerated response to vasopressors, and the blood pressure cuff occasionally needs
             to be replaced by an intra-arterial catheter due to limitations in size)

          2. Height < 5'0" (Women < 5'0" are likely to require a dose of local anesthetic less than
             the standardized dose in this study)

          3. Laboring women

          4. Urgent or emergency cesarean delivery

          5. Hypertensive disease of pregnancy

          6. Severe maternal cardiac disease

          7. Subjects on monoamine oxidase inhibitors (MAOI's) or tricyclic antidepressants

          8. Fetal anomalies or intrauterine fetal death

          9. Failed spinal anesthesia

         10. Subject enrollment in another study involving a study medication within 30 days of CD

         11. Any other physical or psychiatric condition which may impair their ability to
             cooperate with study data collection