Neonatal Acid-Base Status After C Section With Maternal Tilt vs. Supine
Condition: Aortocaval Compression; Fetal Acidosis
MeSH terms: Acidosis
Study type: Interventional

Summary: 
      This study aims to compare the neonatal acid-base status of women who remain supine
      horizontal, with women who are tilted to the left side by 15° during elective cesarean
      delivery at term under spinal anesthesia, with systolic BP maintained at baseline with a
      phenylephrine (PE) infusion. The null hypothesis is that the position of the patient (supine
      horizontal or tilted) during cesarean section will make no difference to neonatal wellbeing.
      The primary outcome will be the neonatal umbilical arterial base deficit (BD) at birth. The
      investigators will also examine the effects of maternal position during cesarean section
      under spinal anesthesia on maternal cardiac output (CO) and whether these changes have a
      correlation with the neonatal umbilical cord blood acid-base status. The secondary outcome
      will be the total phenylephrine dose requirement at 15 minutes after spinal injection.
    

Detailed description: 
      Methods: This will be a randomized trial structured as an equivalence trial. Subjects will be
      American Society of Anesthesiologists (ASA) I and II women aged ≥18 years, non-laboring, at
      term (>37 weeks gestation) with singleton pregnancies in cephalic presentation, scheduled for
      elective cesarean delivery under spinal anesthesia. Patients will receive spinal anesthesia
      for cesarean section in the sitting position, after which they will lay either supine
      horizontal or the surgical table will be tilted to the left by 15°, depending on the group to
      which they were randomized (SUPINE or TILT). An IV phenylephrine infusion will be
      administered to maintain systolic BP at baseline until delivery. A noninvasive hemodynamic
      monitoring system (NICOM, Cheetah Medical Inc., Vancouver, WA, USA) will continuously monitor
      CO and stroke volume. Neonatal umbilical vein and arterial blood gas results will be
      recorded.The null hypothesis is that the position of the patient (supine horizontal or
      tilted) during cesarean section will make no difference to neonatal wellbeing.

      Statistical Design: The estimated sample size is the minimum number of study subjects
      required for rejecting the alternative hypothesis (i.e., accepting the null hypothesis). A
      significant difference between groups in the primary outcome, umbilical artery BD (which is a
      measure of fetal well being at the time of delivery and an indirect indicator of the adequacy
      of uteroplacental perfusion) would be of the order of magnitude of 2 mmol/L. Standard
      deviation of BD tends to be of this magnitude also. It would therefore require 22 subjects
      per group for 90% power to detect this magnitude of difference with alpha 0.05. Because BD is
      often not normally distributed, it is appropriate to increase sample size by 10-20%, and
      because the investigators have important secondary outcomes (PE usage, UA and UV pH, UV BD)
      the investigators intend to recruit 50 subjects per group to allow sufficient power for
      analysis of these secondary outcomes with appropriate correction for multiple comparisons,
      and allowing for 10% dropout. PE usage in the investigators previous study tends to have a
      standard deviation of about 30% of the mean, also roughly the magnitude of a clinically
      significant difference.
    

Intervention name(s): SUPINE; TILT
Intervention type(s): Procedure; Procedure
Intervention description(s): Patients in the SUPINE group will receive spinal anesthesia for cesarean section in the sitting position, after which they will lay supine horizontal on the surgical table.
A phenylephrine intravenous infusion will be titrated according to a set protocol, to maintain the systolic blood pressure at baseline.; Patients will receive spinal anesthesia for cesarean section in the sitting position, after which they will lay on the surgical table, which will be tilted to the left by 15°.
A phenylephrine intravenous infusion will be titrated according to a set protocol to maintain the systolic blood pressure at baseline.
Allocation: Randomized
Intervention model: Factorial Assignment
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: Aortocaval compression; Cesarean Section; Spinal Anesthesia; Phenylephrine