ECMO Patient Monitoring and Assessment 2 — Questions and Answers
Question 1: Which parameter most directly indicates adequate oxygen delivery during ECMO support?
- SpO2 > 95%
- Mixed venous oxygen saturation (SvO2) 65-75% (Correct answer)
- PaO2 > 100 mmHg
- Hemoglobin > 12 g/dL
Correct answer: Mixed venous oxygen saturation (SvO2) 65-75%
SvO2 of 65-75% reflects the balance between oxygen delivery and consumption, indicating adequate systemic perfusion during ECMO.
Question 2: During VV-ECMO, a patient's native SpO2 drops despite stable ECMO flow. What should the clinician assess first?
- Recirculation fraction (Correct answer)
- Circuit clot burden
- Membrane oxygenator function
- Patient's cardiac output
Correct answer: Recirculation fraction
Recirculation occurs when oxygenated blood is re-aspirated by the drainage cannula, reducing effective oxygen delivery and causing SpO2 to drop despite adequate flows.
Question 3: What is the significance of a widening arteriovenous CO2 difference (AVCO2 gap) in an ECMO patient?
- Improved lung recovery
- Inadequate tissue perfusion and anaerobic metabolism (Correct answer)
- Membrane oxygenator failure
- Excessive sweep gas flow
Correct answer: Inadequate tissue perfusion and anaerobic metabolism
A widening AVCO2 gap (>6 mmHg) suggests poor cardiac output and tissue hypoperfusion with anaerobic CO2 production.
Question 4: In VA-ECMO, the 'north-south syndrome' or differential hypoxia is identified by comparing:
- Right radial and femoral arterial blood gas values (Correct answer)
- Pre- and post-membrane blood gases
- SpO2 from the right hand vs. left foot
- Arterial and venous pressures
Correct answer: Right radial and femoral arterial blood gas values
Right radial (upper body, native heart output) vs. femoral (ECMO-oxygenated blood) ABG comparison identifies differential hypoxia when the failing heart ejects desaturated blood to the upper body.
Question 5: Which neurological monitoring tool is most commonly used at the bedside during neonatal ECMO?
- Continuous EEG
- Near-infrared spectroscopy (NIRS) (Correct answer)
- Transcranial Doppler ultrasound
- Bispectral index (BIS)
Correct answer: Near-infrared spectroscopy (NIRS)
NIRS is widely used during neonatal ECMO to continuously monitor cerebral regional oxygen saturation (rSO2) and detect neurological compromise non-invasively.
Question 6: A sudden decrease in ECMO venous drainage pressure (more negative) with unchanged pump speed most likely indicates:
- Hypovolemia or cannula malposition (Correct answer)
- Pulmonary hypertension
- Oxygenator thrombosis
- Increased cardiac recovery
Correct answer: Hypovolemia or cannula malposition
Increasingly negative inlet pressures with unchanged RPM suggest inadequate venous return due to hypovolemia, tamponade, or cannula migration causing 'chatter.'
Question 7: Which laboratory value is most critical to monitor for detecting hemolysis during ECMO?
- Serum creatinine
- Plasma-free hemoglobin (Correct answer)
- Platelet count
- Total bilirubin
Correct answer: Plasma-free hemoglobin
Plasma-free hemoglobin rises when red blood cells are lysed by mechanical shear forces in the circuit, and levels >50 mg/dL indicate significant hemolysis.
ECMO Patient Monitoring and Assessment 2
Which parameter most directly indicates adequate oxygen delivery during ECMO support?