Resus: ECMO Parameters in Obstetric Patients
Extracorporeal membrane oxygenation (ECMO) is a life support technique that can be helpful in cases of cardiovascular and respiratory failure that are unresponsive to traditional resuscitative strategies. During pregnancy, there are physiological changes that occur that make typical ECMO parameters and goals challenging, and these patients in cardiopulmonary distress require unique considerations given that fetal oxygenation and perfusion are also at stake.
Indications for ECMO During Pregnancy:
Respiratory failure: refractory ARDS, status asthmaticus, aspiration, bridge to lung transplant, sepsis, and hypertensive disorders of pregnancy
Cardiogenic shock: cardiac failure, peripartum cardiomyopathy, malignant arrhythmias, myocardial infarction, pulmonary hypertension, amniotic fluid embolism, pulmonary embolism, and intoxications
Cardiac arrest
Physiological Changes During Pregnancy:
There are various physiological adaptations that occur during pregnancy that affect cardiopulmonary function. Elevated serum progesterone leads to increased respiratory drive along with increased tidal volume and minute ventilation. As the pregnancy progresses, second trimester patients develop respiratory alkalosis with compensatory metabolic acidosis, correlating to decreased PaCO2 and bicarbonate compared to non-pregnant patients. This is physiologically helpful during pregnancy because of the advantageous pressure gradient for fetal gas exchange. The presence of a fetus additionally leads to increased oxygen requirements, as the body requires 20% more oxygen to adequately perfuse both mother and fetus.
Cardiac function is also altered during pregnancy, with these patients often having elevated stroke volume, heart rate, cardiac contractility, and cardiac output (up by 30-40%) from baseline. Cardiac output peaks immediately after delivery, with up to a 150% increase in cardiac output from baseline in the setting of strain from labor and delivery. Additionally, elevated progesterone promotes smooth muscle relaxation, leading to decreased systemic and pulmonary vascular resistance (Naoum et al. 2024) (Wong et al. 2022) (Wong et al. 2024) (Yeomans and Gilstrap 2005).
ECMO Parameters and Goals During Pregnancy
To date, there is no robust clinical trial data for optimal ECMO settings during pregnancy, but several review articles have offered current best practices (Naoum et al. 2024) (Wong et al. 2022) (Wong et al. 2024).
Flow Rate: To accommodate increased cardiac output, ECMO flow rates of 100 to 120 mL/kg/min (5–6 L/m2/min) should be initiated in pregnant populations compared to the standard 60 to 80 mL/kg/min (3–4 L/m2/min) in non-pregnant patients.
Oxygenation Goal: Since pregnancy corresponds with increased oxygen demand, usual SaO2 goals of >80% are not viable for pregnant patients, and the ideal minimum maternal SaO2 should be >90%. According to one review, in clinical practice, ECMO levels are often titrated to SaO2 >95%, with constant monitoring for fetal decelerations or other abnormalities to indicate switching to a higher ECMO flow rate (Wong et al. 2024). This translates to PaO2 targets of >70mmHg.
Blood Gas Goals: PaCO2 ideally should match a target of 28-32 mmHg since deviations from this goal can be associated with fetal hypoxemia and acidosis. Pregnant patients should also have a goal pH of greater than 7.4 given that maternal acidosis is poorly tolerated by the fetus. Bicarbonate levels are reduced during pregnancy secondary to chronic respiratory alkalosis and patients on ECMO should fall between 18-21 mmol/L.
Positioning: Left lateral tilt of 15 to 30 degrees that promotes left uterine displacement is ideal to mitigate the effects of aortocaval compression on the venous drainage cannula.
Conclusion
ECMO is a useful tool for the cardiopulmonary support of antepartum and postpartum patients and shows promising rates of maternal and fetal survival. In one systematic review from JAHA, the 30‐day survival rate after use of ECMO during the peripartum or postpartum period was found to be 75.4% for mothers and 64.7% for fetuses (Naoum et al. 2020). However, current evidence for ECMO in obstetric patients is primarily derived from case reports and retrospective reviews, which prove difficult in guiding standardized protocols. More clinical trial data is imperative to identify safe and effective parameters in this special population.
AUTHORED BY: SAILAKSHMI KUMAR, MS4, CWRU SOM
FACULTY EDITING BY: COLIN MCCLOSKEY, MD
References
Ong, J., et al. "Extracorporeal membrane oxygenation in pregnancy and the postpartum period: a systematic review of case reports." International Journal of Obstetric Anesthesia 43 (2020): 106-113.
Naoum, Emily E., et al. "Extracorporeal Life Support in Pregnancy: A Systematic Review." Journal of the American Heart Association 9.13 (2020).
Naoum, Emily E., Erika R. O’Neil, and Amir A. Shamshirsaz. "Extracorporeal membrane oxygenation (ECMO) in pregnancy and peripartum: a focused review." International Journal of Obstetric Anesthesia 60 (2024).
Wong, Michael J., et al. "Extracorporeal membrane oxygenation for pregnant and postpartum patients." Anesthesia & Analgesia 135.2 (2022): 277-289.
Wong, M. J., B. S. Kodali, and S. Rex. "Extracorporeal Membrane Oxygenation and Pregnancy." Best Practice & Research Clinical Anaesthesiology (2024).
Yeomans, Edward R., and Larry C. Gilstrap III. "Physiologic changes in pregnancy and their impact on critical care." Critical care medicine 33.10 (2005): S256-S258.