ECMO - Extracorporeal Membrane Oxygenation Patient Monitoring and Assessment Questions and Answers — Questions and Answers
Question 1: A patient on femoral VA ECMO for cardiogenic shock has stable blood pressure and ECMO flows, but their serum lactate remains elevated at 6 mmol/L after 12 hours. Which of the following is the most crucial assessment to perform next to investigate the persistent hyperlactatemia?
- Perform a thorough neurological exam.
- Obtain a chest X-ray to check for pulmonary edema.
- Increase the ECMO pump flow by 10%.
- Assess perfusion of the cannulated and non-cannulated limbs. (Correct answer)
Correct answer: Assess perfusion of the cannulated and non-cannulated limbs.
Persistent hyperlactatemia despite adequate central hemodynamics on peripheral VA ECMO is a red flag for regional hypoperfusion. The most common and critical cause is limb ischemia in the cannulated leg due to the large arterial cannula obstructing native blood flow. This must be assessed immediately via physical exam, Doppler ultrasound, or NIRS monitoring on the limb. While other causes exist, this is a frequent, reversible, and limb-threatening complication that takes precedence.
Question 2: A routine blood gas analysis from the ECMO circuit shows a pre-oxygenator PaO2 of 40 mmHg and a post-oxygenator PaO2 of 150 mmHg. The sweep gas blender is set to 100% FiO2. What is the most likely interpretation of these findings?
- The patient's native lung function has significantly improved.
- The oxygenator is failing and requires imminent change-out. (Correct answer)
- There is significant recirculation of oxygenated blood.
- The blood pump is malfunctioning, causing inadequate flow.
Correct answer: The oxygenator is failing and requires imminent change-out.
A properly functioning membrane oxygenator, when supplied with 100% oxygen sweep gas, should be able to achieve a post-oxygenator PaO2 of 300-500 mmHg. A post-oxygenator PaO2 of only 150 mmHg indicates a severe diffusion impairment across the membrane. This is most commonly caused by thrombus formation or fibrin deposition on the membrane surface, signifying oxygenator failure and the need for replacement.
Question 3: While monitoring a patient on VA ECMO with bilateral cerebral Near-Infrared Spectroscopy (NIRS), you note a sudden, unilateral drop of 25% from baseline on the left side. Which of the following is the most appropriate initial action?
- Check the patient's head position and rule out external compression. (Correct answer)
- Increase the sweep gas flow to reduce PaCO2.
- Administer a fluid bolus to increase cardiac output.
- Request an immediate oxygenator change-out.
Correct answer: Check the patient's head position and rule out external compression.
A unilateral drop in NIRS readings suggests a focal cerebral perfusion issue. Before escalating to major interventions or assuming an intracranial catastrophe, simple and correctable causes must be ruled out immediately. Head rotation can compress the jugular vein or carotid artery, leading to a drop in regional oxygen saturation (rSO2) on that side. Correcting the head position is the quickest and most appropriate first step. If this does not resolve the issue, further investigation for stroke or other complications is warranted.
Question 4: A 50-year-old patient on VV ECMO for ARDS has a PaCO2 that has risen from 45 mmHg to 60 mmHg over four hours. The ECMO pump flow is stable, and the patient's metabolic state is unchanged. Which parameter on the ECMO circuit should be adjusted first to directly address the hypercapnia?
- Increase the pump RPM to increase blood flow.
- Increase the FiO2 on the gas blender.
- Increase the sweep gas flow rate. (Correct answer)
- Decrease the patient's ventilator respiratory rate.
Correct answer: Increase the sweep gas flow rate.
In an ECMO circuit, carbon dioxide removal is almost entirely dependent on the sweep gas flow rate. Increasing the flow of gas (the 'sweep') across the membrane creates a steeper concentration gradient for CO2, facilitating more efficient diffusion from the blood into the gas phase. Increasing pump flow or FiO2 primarily affects oxygenation. Decreasing the ventilator rate would worsen hypercapnia.
Question 5: When Continuous Renal Replacement Therapy (CRRT) is integrated into the ECMO circuit, where are the access and return lines typically placed to minimize risks of air embolism and circuit pressure disturbances?
- Access pre-pump, return post-oxygenator
- Access post-pump, return pre-pump
- Access post-oxygenator, return post-oxygenator
- Access post-pump (pre-oxygenator), return pre-pump (in the venous drainage line) (Correct answer)
Correct answer: Access post-pump (pre-oxygenator), return pre-pump (in the venous drainage line)
The safest and most common configuration is to access blood from a positive-pressure area of the circuit (post-pump, but before the oxygenator) and return it to a negative-pressure area (pre-pump, on the venous drainage line). Drawing from a positive pressure area prevents air from being entrained into the circuit if a connection becomes loose. Returning to the low-pressure venous line minimizes the resistance the CRRT machine must pump against, preventing alarms and circuit disruption.
Question 6: Which of the following clinical findings is the most direct and visually apparent indicator of significant intravascular hemolysis in a patient on ECMO?
- A progressive drop in the patient's platelet count.
- Dark, tea-colored urine in the urinary drainage bag. (Correct answer)
- An increase in the oxygenator pressure gradient.
- A gradual decrease in the patient's hematocrit.
Correct answer: Dark, tea-colored urine in the urinary drainage bag.
Significant intravascular hemolysis releases large amounts of cell-free hemoglobin into the plasma. This free hemoglobin is filtered by the kidneys, resulting in hemoglobinuria. This classically presents as dark reddish-brown or "tea-colored" urine and is often the most striking and earliest visual sign of severe hemolysis. While falling platelets, rising oxygenator pressures, and falling hematocrit can be associated with hemolysis, they are less specific and not as visually direct as hemoglobinuria.
ECMO - Extracorporeal Membrane Oxygenation Patient Monitoring and Assessment Questions and Answers
A patient on femoral VA ECMO for cardiogenic shock has stable blood pressure and ECMO flows, but their serum lactate remains elevated at 6 mmol/L after 12 hours.
Which of the following is the most crucial assessment to perform next to investigate the persistent hyperlactatemia?