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Electrical cardiometry demonstrates the hemodynamics of aortocaval compression during labor.
Abstract Number: S-57
Abstract Type: Case Report/Case Series
Avoidance of aortocaval compression (ACC) has long been known to be important in obstetrics but ACC has been impossible to detect easily and in real time. Hence, maternal position changes to treat maternal hypotension and fetal bradycardia are empirical. Electrical cardiometry (EC), a method of deriving stroke volume from an impedance cardiography signal, may provide an easy, real-time means of detecting and avoiding ACC.
We present examples of laboring patients in whom adoption of the full left lateral decubitus position (L90) is associated with a secular increase in average cardiac index (CI) and the appearance of further cyclical increases in CI which occur 24-50 seconds after uterine contractions. We call these cyclical increases in CI “autotransfusion waves” (AT waves) and hypothesize that they are due to autotransfusion in the presence of an unobstructed inferior vena cava. We further hypothesize that it is ACC in certain maternal positions which causes the average CI to decrease and the AT waves to disappear. Thus, we hypothesize that maximization of cardiac output (CO) in labor can serve as a marker for the relief of ACC.
Despite the lack of “gold standard” validation for EC in obstetric patients, the regularity and timing of the increases in CI after intrauterine pressure catheter (IUPC) - proven uterine contractions is strong evidence that these increases in CI are caused by the uterine contractions. Furthermore, the absolute value of the increase in CI does not have to be correct for the measurements to be of value as a marker for uterine contractions in the presence of unobstructed venous return. Hence, EC may allow cardiac output (CO) -guided positioning of the laboring patient to promote optimal venous return, blood pressure and placental perfusion. Avoidance of ACC and uterine venous congestion might also improve myometrial function and reduce dysfunctional labor.
Uterine contractions, like positive pressure ventilation, periodically present the heart with increased venous return and further analysis of AT waves might show where the heart is on its Starling Curve.
Figure: Patient with epidural, right side down, receiving pressors until she turns to full left lateral decubitus position (L90), after which blood pressure and CI increase. In L90, AT waves appear and force and frequency of uterine contractions increase-- consistent with relief of ACC. PE50 = phenylephrine 50 mcgm; EPH10 = ephedrine 10 mg. R90, R30 = patient right side down, de