Position therapy in pregnancy: Can trending maternal cardiac output put it on a more objective foundation?

Abstract

Avoiding the “supine hypotensive syndrome of pregnancy” has been a basic concept in patient management since at least the 1950s, and in 1983 Spinapolice et al1 showed that 4 hours of rest per day in the left lateral decubitus position decreased the incidence of preeclampsia in a group of patients at risk for the disease. More recently, the avoidance of falling asleep in the supine position has been advocated as a means of reducing the risk of stillbirth. With respect to managing patients with intra-abdominal hypertension or abdominal compartment syndrome, Lozada et al2 discussed the importance of left uterine displacement and body position in general and advocated the use of intravesical pressure to guide therapy. Currently, the success or failure of maternal positioning is judged by (a) direct fetal assessment (eg, heart rate), (b) intravesical pressure, (c) maternal heart rate and blood pressure, and (d) maternal symptoms such as light-headedness, nausea or generalized discomfort. However, although these criteria are valuable, they have their limitations and logistical shortcomings. Much of the rationale for position therapy in obstetrics has to do with ensuring abdominal organ function, and unobstructed venous drainage is highly important to that function. For this reason, I have suggested the trending of maternal cardiac output as an additional method for judging the success of maternal positioning. A positional reduction in maternal cardiac output serves as a marker for obstruction of the inferior vena cava or its tributaries within the abdomen, together with the lack of adequate collaterals.3 Venous return determines cardiac output in a steady state, so a reduction in venous return due to positional obstruction of abdominal veins will present as a prompt reduction of cardiac output, and electrical cardiometry now offers a safe, continuous, real-time, hands-free, and objective method for trending cardiac output.4, 5 Certainly, obstructed abdominal venous return is not the only threat to organ function in abdominal compartment syndrome. The patient may have an obese abdominal wall, edematous bowel, increased intraluminal contents, massive ascites or other pathologies that produce a generalized increase in intra-abdominal pressure, but even many of these processes have a positional component. Therefore, the correction of any positional abdominal venous obstruction would seem to be “low hanging fruit” in the management of pregnant patients. Even in ambulatory patients at risk for pregnancy complications, screening for positional reductions in cardiac output might be beneficial during the second half of pregnancy. Figure 1 illustrates how cardiac output-guided maternal positioning might alleviate positional venous obstruction and improve abdominal organ function, both in critically ill and in apparently healthy patients.