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ECMO Physiology & Gas Exchange Flashcards

7 cards from real CES practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. Recirculation fraction in VV-ECMO can best be minimized by:

    Answer: Optimizing cannula positioning to maximize distance between drainage and return ports

    Positioning the drainage and return cannulas far apart (e.g., femoral drainage with internal jugular return) minimizes the probability that oxygenated blood is immediately re-drained.

  2. During VA-ECMO, left ventricular distension may develop due to:

    Answer: Increased LV afterload from ECMO arterial return that the failing ventricle cannot overcome

    VA-ECMO increases LV afterload by returning oxygenated blood to the arterial system; a failing ventricle may be unable to eject against this elevated afterload, causing distension.

  3. Which parameter best reflects the overall adequacy of systemic oxygen delivery during ECMO support?

    Answer: Mixed venous oxygen saturation (SvO2) or central venous oxygen saturation (ScvO2)

    SvO2/ScvO2 reflects tissue oxygen extraction and is the most reliable indicator of whether total DO2 meets VO2 demands in ECMO patients.

  4. The maximum achievable post-oxygenator blood oxygen saturation in a properly functioning ECMO oxygenator is typically:

    Answer: 95–100%

    A functioning membrane oxygenator with 100% FDO2 sweep gas should fully saturate blood passing through it, achieving post-oxygenator saturations of 95–100%.

  5. Persistent metabolic acidosis in an ECMO patient with adequate circuit flows and a functioning oxygenator most likely indicates:

    Answer: Inadequate total oxygen delivery relative to metabolic oxygen consumption

    When tissues consume more oxygen than is delivered, anaerobic metabolism produces lactic acid, causing metabolic acidosis despite technically adequate ECMO function.

  6. The primary reason for targeting higher hemoglobin levels (e.g., ≥10 g/dL) in ECMO patients compared to general ICU patients is to:

    Answer: Maximize oxygen-carrying capacity and total oxygen delivery (DO2)

    Since DO2 = CO × CaO2 and hemoglobin is the primary oxygen carrier, maintaining higher Hgb significantly increases CaO2 and total DO2 in ECMO patients with limited cardiac or pulmonary reserve.

  7. The venous drainage (pre-pump) pressure in an ECMO circuit should ideally be maintained at:

    Answer: Mildly negative (approximately -20 to -80 mmHg)

    Mildly negative pre-pump pressures indicate adequate venous drainage without excessive suction; highly negative pressures suggest hypovolemia or cannula obstruction and risk hemolysis and cavitation.