A 22-year-old male is admitted to the ICU with acute respiratory distress syndrome secondary to pneumonia. The clinical course is complicated by progressive hypoxemia, which does not improve with prone ventilation. VV ECMO is instituted with a 31 Fr right internal jugular double-lumen cannula, and the pump flow is at 4.5 L/min. The patient has a HR of 90/min, BP of 110/70 mm Hg with a norepinephrine infusion at 0.05 µg/kg/min, and a SpO2 of 90%. One hour later, the ECMO specialist mentions of “chugging” in the drainage circuit with low inlet pressures. The ECMO flow has reduced to 3 L/min. There is a drop in SpO2 to 84%, and the norepinephrine requirement has increased to 0.1 µg/kg/min. An arterial blood sample sent to the critical care laboratory reveals:
The most appropriate next step in management is to:
A. Start epinephrine to improve cardiac contractilityCorrect Answer: D
“Chugging” or “chattering” of the ECMO circuit refers to back and forth swinging of the drainage and return tubes. This occurs because of fluctuations in venous drainage pressures. Hypovolemia and high pump speeds are two common scenarios where chugging can occur. In both cases, increased negative pressure at the venous inflow port of the drainage cannula leads to a temporary venous collapse. This causes low flows through the ECMO circuit even at high pump speeds, and hence increasing ECMO pump flows will not help (B). The normal negative pressure in the drainage cannula is between -50 to -80 mm Hg. Pressures lower than -100 mm Hg are abnormal and are seen during chugging episodes. The hypovolemia can be treated by administering a fluid bolus (D).
In the presence of chugging, the patient should be evaluated for signs of low intravascular volume. Tachycardia and hypotension may be present requiring vasopressor initiation or up titration. There might be desaturation due to decreased ECMO flows. Management involves administration of fluid bolus or blood transfusion if hematocrit is low. Inotropes are not usually required if baseline cardiac function is normal (A). Because the hematocrit is normal, the patient does not need a blood transfusion (C). Point of care ultrasound can be utilized to guide hemodynamic management. The ECMO pump speed can be reduced temporarily to decrease the flows to avoid chugging and subsequent venous suck down.
Low ECMO flows despite high pump speeds can also be encountered when there is some obstruction in the circuit. Obstruction could be due to kinking of the tubes or due to the presence of blood clots in the oxygenator. Isolated postoxygenator tubing chugging can be due to high flows and unrelated to hypovolemia. It is also important to rule out malposition of the cannulas.
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