ECMO Circuit Components and Management 4 — Questions and Answers
Question 1: What is the primary hemodynamic difference between VA-ECMO and VV-ECMO?
- VA-ECMO provides both cardiac and respiratory support while VV-ECMO provides respiratory support only (Correct answer)
- VV-ECMO increases afterload while VA-ECMO reduces it
- VA-ECMO can only be used in pediatric patients
- VV-ECMO requires arterial cannulation
Correct answer: VA-ECMO provides both cardiac and respiratory support while VV-ECMO provides respiratory support only
VA-ECMO bypasses both the heart and lungs providing cardiorespiratory support, whereas VV-ECMO only supports gas exchange with no direct cardiac output augmentation.
Question 2: The centrifugal pump used in modern ECMO circuits generates flow by:
- Magnetically levitated or bearing-mounted impeller creating a pressure gradient via centrifugal force (Correct answer)
- Sequential compression of tubing by rotating rollers
- Pneumatic pressure applied to a blood sac
- Electromagnetic induction in a metal chamber
Correct answer: Magnetically levitated or bearing-mounted impeller creating a pressure gradient via centrifugal force
Centrifugal pumps use a spinning impeller (constrained or magnetically levitated) to impart kinetic energy to blood, generating flow through centrifugal force.
Question 3: When performing an emergency hand-crank during a centrifugal pump power failure, the specialist should:
- Maintain a minimum of 1.5–2 L/min flow to prevent circuit thrombosis and clamp lines if unable to hand-crank (Correct answer)
- Increase sweep gas to maximum FiO2 immediately
- Administer a protamine dose to reverse anticoagulation
- Convert to a roller pump using backup tubing
Correct answer: Maintain a minimum of 1.5–2 L/min flow to prevent circuit thrombosis and clamp lines if unable to hand-crank
During pump failure, maintaining minimal flow via hand-crank prevents stasis thrombosis; if hand-cranking is not feasible, clamping both limbs prevents backflow and air entrainment.
Question 4: The purpose of the heat exchanger integrated into the ECMO oxygenator is to:
- Maintain normothermia or induce therapeutic hypothermia by warming or cooling circulating blood (Correct answer)
- Remove lipid microemboli before return to the patient
- Increase oxygen solubility before arterial reinfusion
- Regulate sweep gas humidity to prevent fiber desiccation
Correct answer: Maintain normothermia or induce therapeutic hypothermia by warming or cooling circulating blood
The heat exchanger circulates water at a controlled temperature around the blood path, enabling precise temperature management including therapeutic cooling.
Question 5: Flow monitoring via ultrasonic flow probes on the ECMO circuit measures flow based on:
- Transit-time ultrasound detecting changes in sound wave travel time caused by moving blood (Correct answer)
- Doppler shift frequency from red blood cell velocity
- Pressure differential across a fixed orifice
- Electromagnetic induction proportional to blood conductivity
Correct answer: Transit-time ultrasound detecting changes in sound wave travel time caused by moving blood
Transit-time ultrasound flow probes measure the time difference between upstream and downstream ultrasonic pulses, which correlates directly to volumetric blood flow.
Question 6: A sudden decrease in ECMO circuit flow with a simultaneous rise in pump RPM most likely indicates:
- Increased circuit afterload from an arterial cannula obstruction or kink (Correct answer)
- Improved native cardiac recovery
- Air lock in the venous drainage limb
- Oxygenator plasma leakage
Correct answer: Increased circuit afterload from an arterial cannula obstruction or kink
When pump RPM increases but flow drops, the pump is working harder against increased resistance, suggesting an outflow obstruction such as arterial cannula kinking or high vascular resistance.
Question 7: What is the significance of the 'mixed venous saturation' (SvO2) measured from the ECMO drainage limb?
- It reflects the balance between systemic oxygen delivery and consumption, guiding adequacy of ECMO support (Correct answer)
- It measures oxygenator efficiency by comparing pre- and post-membrane O2 content
- It determines the need for anticoagulation adjustments
- It indicates the degree of pulmonary shunting in VV-ECMO
Correct answer: It reflects the balance between systemic oxygen delivery and consumption, guiding adequacy of ECMO support
Drainage line SvO2 represents the mixed venous blood entering the circuit and indicates whether oxygen delivery meets metabolic demand across the whole body.
ECMO Circuit Components and Management 4
What is the primary hemodynamic difference between VA-ECMO and VV-ECMO?