A 36-year-old woman presented to urgent care with a 1-week history of cough, fever and dyspnea. On examination, she was mildly tachypneic (20) and tachycardic (114) with bilateral rales. Her room air oxygen saturation was 87 percent. Chest x-ray showed diffuse bilateral infiltrates. She was placed on 4 liters nasal cannula and transported by EMS to the local emergency department (ED) where her oxygen saturation had fallen to 87 percent on 6 liters nasal cannula. She was transitioned to a non-rebreather mask with improvement in oxygenation to 94 percent. She was able to speak in short sentences, but appeared dyspneic. ECG showed sinus tachycardia with no ischemic changes. Labs were notable for a hemoglobin of 9.9 g/dL, carbon dioxide 20 mmol/L and anion gap 13 mmol/L. The white blood cell count, liver function and coagulation studies were normal. 

One hour after arrival to the ED, she was briefly trialed off the non-rebreather and desaturated to 80 percent on 6 liters nasal cannula. She was still notably dyspneic with speaking, but had no accessory muscle use. She was given a 30 mL/kg bolus of crystalloid and empirically treated for community acquired pneumonia with ceftriaxone and azithromycin. A rapid flu test and respiratory viral PCR were sent. 

Three hours after arrival, the critical care team was consulted for admission to the ICU given her high flow oxygen requirement. On evaluation, she was now in severe respiratory distress with an SpO2 of 80% on a non-rebreather. She underwent rapid sequence intubation for acute hypoxemic respiratory failure without complication. An arterial line was inserted. A chest x-ray performed after intubation showed progression of bilateral opacities. Post-intubation arterial blood gas demonstrated the following: pH 7.11, PaCO2 63, PaO2 77, HCO3 16 on pressure regulated volume control low tidal volume ventilation with Vt 350 mL (6 mL/kg ideal body weight), FiO2 100%, PEEP 10 cm H20 and respiratory rate of 30. Plateau pressure was 31 cm H20 with a driving pressure of 21 cm H20 and static lung compliance of 17 mL/cm H20. A cisatracurium bolus and infusion and inhaled epoprostenol were administered in the setting of severe acute respiratory distress syndrome (ARDS). 

Two hours after intubation, her mean arterial pressure drifted down to 64 mm Hg and a central line was inserted. Point of care ultrasound was performed demonstrating normal biventricular contractility and size ratio and no pericardial effusion. At this point, a qualitative urine pregnancy test was noted to be positive. Transabdominal ultrasound subsequently revealed a fetus with estimated gestational age of 23 weeks and 6 days with heart rate of 130. Betamethasone 12 mg was administered intravenously.  

On hour later, she was noted to have refractory hypoxemia and respiratory acidosis with ABG demonstrating pH 6.91, PaCO2 69 and PaO2 78, HCO3 10. Prone positioning was deferred due to the rapid progression of her ARDS. The ECMO team was consulted and she was taken to the OR for venovenous ECMO cannulation with a 31 French dual lumen catheter. Post-cannulation, her oxygen saturation rose to 100 percent and PaCO2 normalized on a flow of 3.5 L/min and sweep gas flow of 6 L/min. 

What is the role of ECMO in the pregnant patient? A study published in the May 2020 issue of Critical Care Medicine examined the survival of 263 peripartum patients from the international ELSO registry who received VA or VV ECMO between 1997 and 2017. The primary outcome measure was in-hospital mortality. A multiple logistic regression model for nonsurvivors was developed to identify risk factors for mortality. The authors found that VA ECMO was the primary modality used (49.6% patients), 43.8% received VV ECMO with 6.6% of patients receiving either hybrid ECMO or conversion between modes. The primary indications for ECMO were respiratory failure followed by cardiogenic shock and ECPR for cardiac arrest. Among patients with pulmonary indications for ECMO, overall mortality was 30.9%. For patients with pneumonia or influenza, mortality was lower at 22.2%. There was no difference in mortality when modes of ECMO were compared (VV 23.9% vs VA 34.4%) or indication (pulmonary vs. cardiac). Pregnant patients who received ECMO for pulmonary indications had 76.1% survival compared to 54.8% survival for ECPR. Renal complications and longer duration of ECMO support were identified as risk factors for mortality. Hemorrhagic complications were reported in 37.3% of pregnant patients. 

What was the outcome of our patient? Respiratory viral PCR was positive for human metapneumovirus. After cannulation for VV ECMO, she was transitioned to ultra-protective ventilation with 4 cc/kg IBW tidal volume; however, driving pressure remained > 15 cm H20. The tidal volume was further reduced to 2.5 cc/kg IBW. On day 2 of ECMO support, she required emergent circuit change for oxygenator failure, which she tolerated well. She was diuresed with a furosemide infusion on day 3 with improvement in static lung compliance from 17 mL/cm H20 on cannulation to 28 mL/cm H20 on day 4 of ECMO. On day 5, tidal volume was increased to physiologic level and the sweep gas flow rate was weaned to 1 L/min. On day 6, she was recirculated on a sweep of 0 L/min and was successfully decannulated. She was extubated to nasal cannula on day 7. Four months later, a healthy baby boy with an APGAR of 9 was delivered via c-section.    

The overall survival rate of 70% in peripartum patients is greater than the general population, where overall survival of adults with respiratory failure is 59% and cardiac failure is 42%. ECMO shoulder be considered for pregnant patients with severe ARDS and progression to refractory hypoxemia and respiratory acidosis.  

References: 

Ramanathan K, et al. Extracorporeal membrane oxygenation in pregnancy: an analysis of the extracorporeal life support organization registry. Critical Care Medicine 2020;48(5):696-703.