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Board Questions

1. Your patient is on VV ECMO for ARDS and their lactate level is rising. Which of these is the LEAST effective way to improve oxygen delivery? 

a) Increase the flow of oxygen to the oxygenator
b) Increase the flow on the ECMO circuit
c) Transfuse pRBCs
d) Increase the FIO2 of the ventilator

2. Which of the following would NOT affect your achievable ECMO flow? 

a) Cannula size
b) Patient volume status
c) RPMs on ECMO pump
d) Sweep gas

3. Which of the following is NOT involved in trialing off VV ECMO? 

a) Increasing ventilator support
b) Turning off the sweep gas
c) Intermittent clamping/flashing of the ECMO circuit
d) Intermittent measurement of oxygenation/ventilation

4. Which of the following is NOT a contraindication to ECMO?

a) Grade III IVH
b) Irreversible disease process
c) Septic shock
d) Refusal to receive blood products



ANSWERS & EXPLANATIONS

1. A. Oxygen delivery is the product of the oxygen content (Hgb* 1.32* O2 Saturation + 0.003 PaO2) and the cardiac output. In a patient on VV ECMO, oxygenated blood comes primarily from the ECMO circuit with some smaller contribution from the patient's diseased lungs. Turning up ECMO flow effectively captures a larger proportion of the cardiac output and thus oxygenates a greater percentage of the patient's blood. Similarly, turning up the FIO2 will more effectively oxygenate the blood that flows through the patient's lungs (all of the CO in a patient on VV ECMO) although in general, FIO2 is kept <50-60% to avoid oxygen toxicity. Transfusing pRBC's leads to an increase in oxygen content. Increasing oxygen flow through the oxygenator may improve ventilation but in general will have little/no effect on your post oxygenator oxygen content as the blood that exits the oxygenator is typically nearly fully saturated.

2. D. The sweep gas affects ventilation but has no effect on ECMO flow (aside from arguments that could be made regarding acid/base status and PVR and SVR). The patient's volume status, cannula sizes, and RPMs on the pump all directly affect what flows may be achievable. 

3. C Clamping and flashing are only required for trialing off VA ECMO as removing the sweep gas effectively removes any ECMO support when on VV ECMO but creates a large right to left shunt when on VA ECMO. 

4. C While septic shock used to be a relative contraindication for ECMO, it is now included in the Surviving Sepsis Guidelines as a potential therapeutic modality when refractory to other less invasive treatments


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