Extracorporeal Membrane Oxygenation for Pregnant and Postpartum Patients

Michael J. Wong, MD; Shobana Bharadwaj, MBBS; Jessica L. Galey, MD; Allison S. Lankford, MD; Samuel Galvagno, DO, PhD; Bhavani Shankar Kodali, MD

Disclosures

Anesth Analg. 2022;135(2):277-289. 

In This Article

Uteroplacental Perfusion

At term, uterine oxygen consumption is approximately 25 mL/min, primarily due to fetal and placental demands.[64] Fetal oxygenation is maintained by numerous physiologic adaptations, including leftward shift of the fetal oxygen-hemoglobin dissociation curve, high fetal cardiac output, fetal polycythemia, and distribution of fetal blood flow to vital organs.[65,66] However, fetal oxygen delivery may be precarious in the critically ill pregnant patient due to upstream effects of maternal hypoxemia, hypovolemia, anemia, and acidosis on uterine perfusion. Uterine blood flow is poorly autoregulated and depends on maintaining a uterine perfusion pressure greater than uterine vascular resistance.[67] Aortocaval compression by the gravid uterus may impair maternal venous return, cardiac output, and subsequent uteroplacental perfusion. Hence, after 20 weeks gestation, patients should be positioned in left lateral decubitus position or have a cushion under their right hip while they are supine.[12,42,68,69] Prone positioning should result in complete resolution of aortocaval compression, provided the patient is adequately padded to offload the gravid uterus. Other factors impairing uteroplacental blood flow include systemic hypotension, hypovolemia, hypothermia, as well as circulating catecholamines and exogenous vasoconstrictors. Femoral vein cannulation itself may theoretically increase venous backpressure within the uterine vasculature and reduce uteroplacental perfusion.[70] Because of this, continuous fetal monitoring during cannulation can provide real-time feedback on disruption of uteroplacental blood flow by the cannula and indicate a need to withdraw it slightly.

The specific impact of VA-ECMO on uterine circulation is unknown, though animal models of cardiopulmonary bypass demonstrate less effective uteroplacental perfusion with nonpulsatile flow compared to pulsatile flow.[71] Accordingly, continuous fetal monitoring is particularly desirable during VA-ECMO, where the nonpulsatile nature of the ECMO pump may provide somewhat reduced uteroplacental perfusion compared to the native heart. If the fetal heart rate tracing becomes nonreassuring, augmentation of maternal blood pressure or increased ECMO flow may help avoid an emergent delivery. Limited case reports have also suggested the use of an intraaortic balloon pump can mimic physiologic, pulsatile blood flow and potentially improve fetal well-being during cardiopulmonary bypass.[72]

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