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Effect of maternal supine horizontal position versus 15° left lateral table tilt during cesarean delivery under spinal anesthesia on neonatal acid-base status
Abstract Number: O1-04
Abstract Type: Original Research
Left lateral uterine displacement during cesarean delivery (CD) is ingrained in obstetric anesthesia practice. Studies from the 1970’s reported improved neonatal status with maternal tilt during CD, although many women were tilted right, anesthetic techniques varied, and hypotension was poorly controlled.1 Traditionally, 15° tilt is attempted, based on the “Crawford wedge”, but is almost never achieved.2 MRI imaging indicates that at term, the inferior vena cava (IVC) is almost completely compressed in both the supine position and with 15° left lateral tilt but that IVC volume increases with 30° tilt. The aorta is not compressed in any position.3 This suggests that left tilt may not accomplish what the literature and textbooks have assumed it does. We hypothesized that with contemporary obstetric anesthesia care, 15° left lateral tilt may not be indicated and conducted a randomized clinical trial comparing neonatal acid-base status in women who were completely supine vs. tilted left by 15°.
Healthy women, with a singleton term fetus, undergoing elective CD with a spinal anesthetic (bupivacaine 12mg, fentanyl 15mcg, morphine 150mcg) were randomized to supine horizontal (SUPINE, N=50)) or to 15° left lateral tilt of the surgical table (TILT, N=47)) following spinal injection. A lactated Ringer’s 10ml/kg coload and a phenylephrine (PE) infusion titrated to achieve 100% baseline systolic BP (SBP) were initiated at the time of the spinal dose.4 The primary outcome was umbilical artery (UA) base excess (BE). The study was powered as a non-inferiority study with > 90% power to determine that UA BE was not more than 1.0 mmol/L worse in the supine versus tilted group.
Results: There were no differences in umbilical artery or vein BE or pH between groups (Table). One neonate in each group required bag-mask ventilation, and one in the TILT group had an Apgar of 5 at 1 min; the 5 min Apgar score was 9 in all cases.
Not tilting the surgical table by 15° during CS with spinal anesthesia does not impair neonatal acid-base status compared to the tilt position, when baseline SBP is maintained with a PE infusion. Our data suggests that current recommendations on maternal positioning during CD under spinal anesthesia may no longer be necessary and are not evidence-based.
1. Crawford, BJA 1972;44:477-84.
2. Jones, BJA 2003; 90; 86-7.
3. Higuchi, Anesthesiology 2015;122:286-93.
4. Odekon, Anesth Analg 2015; 120: 1309-16.