Cardiac Output-Guided Maternal Positioning

Trending maternal cardiac output in real time allows the immediate detection of positional obstruction of uterine venous return by the gravid uterus, since such obstruction causes a reduction of cardiac output within less than a minute. Also, during labor, uterine contractions produce autotransfusion, and if there is no obstruction to uterine venous return, this bolus of autotransfused blood enters the central circulation and rapidly returns to the heart, causing periodic increases in maternal cardiac output which we call “autotransfusion waves.” Positional obstruction to uterine venous return in labor therefore causes two phenomena: (1) a decrease in baseline maternal cardiac output between contractions and (2) a loss of autotransfusion waves. During labor, these two phenomena can be used as early warning signs to reposition the patient before the fetus or myometrium begins to be negatively affected by the decreased uteroplacental perfusion and the increase in uterine venous pressure which normally accompany obstruction to uterine venous return. This use of positional reductions in maternal cardiac output—and loss of “autotransfusion waves” during labor—as a signal to reposition the patient may be termed “cardiac output-guided maternal positioning,” and its use might result in fewer episodes of fetal distress and fewer cesarean deliveries for dysfunctional labor. Practiced earlier in gestation, cardiac output-guided maternal positioning might reduce the incidence or severity of preeclampsia, fetal growth restriction, or preterm birth.