O’Rourke, K. Clinical Anesthesiology. Published online: 5 August 2016
Is there any benefit to the common practice of tilting women during cesarean delivery? A randomized clinical trial suggests maybe not.
“Not tilting the surgical table does not impair neonatal acid–base status compared to the tilt position when baseline systolic blood pressure is maintained with phenylephrine infusion,” said Allison Lee, MD, assistant professor of anesthesiology at NewYork-Presbyterian Hospital/Columbia University Medical Center, in New York City. She presented the study at the 2016 annual meeting of the Society for Obstetric Anesthesia and Perinatology (abstracts 01-04 and 01-05).
For the last 50 years, it has been obstetric anesthesia dogma that clinicians should provide left uterine displacement during cesarean delivery. When pregnant women near term lie in the supine position, the uterus can compress the inferior vena cava causing hypotension, reduced placental perfusion and decreased fetal oxygenation. Most women at term have a completely obstructed inferior vena cava, yet very few have significant hemodynamic consequences. The reason is because of the development of compensatory mechanisms, such as venous constriction in the lower extremities, which promotes flow through collateral venous channels, Dr. Lee explained.
Clinicians have worried, however, that these compensatory mechanisms may disappear under anesthesia.
In the 1970s, a number of studies supported tilting women during cesarean delivery because of improved outcomes in the neonate (e.g., Brit J Anaesth1972;44:477-484). The 15-degree tilt used in most studies is arbitrary, a compromise that still provides access for a surgeon to operate. These older studies are limited because the anesthetic technique used bears little resemblance to what is done in contemporary practice; the studies were not randomized, and it is questionable whether the outcome differences were clinically significant.
Dr. Lee pointed out that a recent study comparing the effect of lateral tilt on the volume of abdominal aorta and inferior vena cava in pregnant and nonpregnant women showed that in parturients, the aorta was not compressed and a 15-degree left-lateral tilt position did not effectively reduce inferior cava compression (Anesthesiology 2015;122:286-293).
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