Cardiac output-guided maternal positioning in pregnancy-- can it improve outcomes?

Chronic and recurrent obstruction of the inferior vena cava by the uterus during the second half of pregnancy are theorized to contribute to the causation of preeclampsia, fetal growth restriction, preterm birth, dysfunctional labor and postpartum uterine atony. Such obstruction is hypothesized to be asymptomatic for the mother but can be detected and minimized by non-invasive continuous trending of maternal cardiac output, because positional decreases in cardiac output can serve as a warning signal of obstruction of venous return. Injury may be caused by 1) decreased cardiac output, 2) increased uterine venous and intervillous pressures and 3) decreased intervillous perfusion. Wide variations in intervillous oxygen tension may be more harmful than low but stable oxygen tension. Clinical examples of asymptomatic but dramatic positional changes in maternal cardiac output in hospitalized patients are shown. Further research should begin with laboring patients, since cardiac output changes dramatically over time and with position during labor.