Critical Care Medicine-Pulmonary Disorders>>>>>Lung Transplantation, Complications, and VV ECMO
Question 6#

A 35-year-old female patient is admitted to the hospital with pneumonia. She was recently diagnosed with end-stage renal disease and is on maintenance dialysis through a tunneled right subclavian dialysis catheter. Hospital course is complicated by respiratory failure and acute respiratory distress syndrome requiring mechanical ventilation. Due to progressive hypoxia, VV ECMO is instituted via bilateral femoral cannulas. Mechanical ventilation is reduced to resting ventilation with a low FiO2 , tidal volume, and respiratory rate. Twelve hours later the patient has a drop in arterial oxygen saturation from her baseline of 94% to 82%. The oxygen saturation of blood drawn from the femoral venous line, which is pre-oxygenator, has increased during the same time from 65% to 80%.

What is the most appropriate next step in management?

A. Increase pump speed
B. Radiographic evaluation of the cannulas
C. Change oxygenator
D. Add an additional parallel ECMO circuit

Correct Answer is B


Correct Answer: B

Increase in oxygen saturation of the pre-oxygenator venous blood with a decrease in arterial oxygen saturation raises the concern for clinically significant recirculation in this patient and hence requires radiographic evaluation of cannula position to verify that the two lumens are separate from each other (B). Recirculation is a phenomenon unique to VV ECMO wherein the oxygenated blood from the return cannula reenters the ECMO circuit through the drainage cannula before reaching the systemic circulation. The distance between the ports of drainage and return cannulas influence the amount of recirculation. Recirculation is also affected by the type of cannulation for VV ECMO. Femoro-femoral and femoral-internal jugular configurations carry higher risks of significant recirculation when compared to a dual-lumen configuration.

Increase in pump speed and ECMO flow rate have shown to be associated with a higher fraction of recirculation (A). Oxygenator failure is fairly unlikely to occur in just 12 hours after initiation of support but can be easily ruled out with a postoxygenator ABG (C). Adding another parallel circuit will not provide any additional benefit, if the cannulas are malpositioned (D). Other factors that may influence recirculation include changes in intrathoracic and intra-cardiac pressures and changes in patient positioning. 

Clinically significant recirculation can lead to hypoxia and subsequent end-organ damage. Management of new-onset recirculation involves radiographic or ultrasound evaluation to check the positions of the drainage and return cannulas. Increasing the distance between the two cannulas by withdrawing the drainage cannula can reduce recirculation. Other strategies to reduce recirculation include addition of a new drainage cannula, use of a bicaval dual-lumen cannula, or manipulation of the reinfusion cannula to direct the return jet toward the tricuspid valve.


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