ECMO Patient Monitoring and Assessment 5 — Questions and Answers
Question 1: Which ECMO parameter directly reflects the efficiency of the membrane oxygenator's gas exchange capacity?
- ECMO blood flow rate (L/min)
- Post-oxygenator PaO2 and PaCO2 (Correct answer)
- Sweep gas FiO2 setting
- Inlet pressure (P-inlet)
Correct answer: Post-oxygenator PaO2 and PaCO2
Post-oxygenator blood gas values directly measure how effectively the membrane is transferring oxygen and removing CO2 from the blood passing through it.
Question 2: During ECMO weaning trials, which clinical parameter best confirms readiness to separate from VV-ECMO support?
- SpO2 > 88% at ECMO flows of 1 L/min with FiO2 0.5 and moderate vent settings (Correct answer)
- SpO2 > 95% with ECMO at full flows
- PaO2 > 200 mmHg on ECMO
- Normal chest X-ray with ECMO at maximum flow
Correct answer: SpO2 > 88% at ECMO flows of 1 L/min with FiO2 0.5 and moderate vent settings
Maintaining acceptable oxygenation at minimal ECMO flows (1 L/min) with reduced FiO2 and moderate ventilation confirms sufficient native lung recovery for safe decannulation.
Question 3: What is the target range for activated partial thromboplastin time (aPTT) in most adult ECMO protocols?
- 20-40 seconds
- 60-80 seconds (Correct answer)
- 100-120 seconds
- 150-180 seconds
Correct answer: 60-80 seconds
Most adult ECMO programs target an aPTT of 60-80 seconds to balance clot prevention within the circuit against systemic bleeding risk from anticoagulation.
Question 4: A patient on VA-ECMO develops low ECMO flows with high RPM, and the circuit pressure alarm activates. After ruling out hypovolemia, the next assessment should be:
- Increase sweep gas flow
- Inspect for cannula kinking or positional obstruction (Correct answer)
- Reduce heparin infusion
- Increase ventilator PEEP
Correct answer: Inspect for cannula kinking or positional obstruction
High RPM with low flows and elevated pressures despite adequate volume suggests mechanical obstruction such as cannula kinking, migration, or outflow obstruction requiring immediate inspection.
Question 5: Cerebral regional oxygen saturation (rSO2) measured by NIRS falls below 50% in an ECMO patient. The first intervention should be:
- Increase vasopressor dose
- Assess and optimize ECMO flow, MAP, hemoglobin, and arterial CO2 (Correct answer)
- Discontinue sedation
- Perform emergent head CT
Correct answer: Assess and optimize ECMO flow, MAP, hemoglobin, and arterial CO2
A rSO2 below 50% signals cerebral oxygen debt; optimizing DO2 determinants — ECMO flow, mean arterial pressure, hemoglobin, and PaCO2 — is the first-line response.
Question 6: Which sign on physical examination specifically suggests cannula-site venous thrombosis in a femoral ECMO patient?
- Bilateral ankle edema
- Unilateral leg swelling, warmth, and discoloration distal to the cannula site (Correct answer)
- Redness at the cannula exit wound only
- Systemic fever above 38.5°C
Correct answer: Unilateral leg swelling, warmth, and discoloration distal to the cannula site
Unilateral swelling, warmth, and discoloration of the limb distal to the femoral cannula indicate deep vein thrombosis or limb ischemia from venous outflow obstruction.
Question 7: Which intervention is indicated when a VV-ECMO patient's sweep gas is at maximum FiO2 but SaO2 remains below 80%?
- Increase heparin infusion
- Evaluate for recirculation and consider cannula repositioning or flow adjustment (Correct answer)
- Decrease PEEP immediately
- Begin vasopressor therapy
Correct answer: Evaluate for recirculation and consider cannula repositioning or flow adjustment
Persistent hypoxia despite maximum sweep gas suggests high recirculation fraction; repositioning cannulas to increase the distance between drainage and return reduces recirculation.
ECMO Patient Monitoring and Assessment 5
Which ECMO parameter directly reflects the efficiency of the membrane oxygenator's gas exchange capacity?