ECMO - Extracorporeal Membrane Oxygenation Complications and Troubleshooting Questions and Answers

Question 1

A patient on VV ECMO for ARDS secondary to an atypical pneumonia is noted to have persistently low pulse oximetry readings (SpO2 85-88%) despite an excellent post-oxygenator PaO2 of >400 mmHg on blood gas analysis. The blood in the arterial line of the ECMO circuit appears unusually dark or 'chocolate brown.' This discrepancy is most suggestive of which complication?

Accepted Answer

Methemoglobinemia

Answer

Methemoglobinemia occurs when the iron in hemoglobin is oxidized to the ferric (Fe3+) state, rendering it unable to bind oxygen. This causes a 'chocolate brown' blood appearance and a functional anemia. Standard pulse oximetry becomes inaccurate, reading falsely low (tending towards 85%), while the PaO2, which measures dissolved oxygen, remains high. The diagnosis is confirmed with co-oximetry.

Question 2

During management of a patient on VA ECMO with a centrifugal pump, you observe that the measured circuit blood flow has suddenly decreased from 4.5 LPM to 2.5 LPM, while the pump RPM has been increased from 3500 to 4000 in an attempt to compensate. Which of the following is the most likely cause for this change?

Accepted Answer

An obstruction in the arterial (return) line

Answer

Centrifugal pumps are afterload-sensitive. A sudden obstruction in the arterial line (e.g., cannula thrombus, kinked tubing, or dissection) increases the resistance (afterload) the pump must work against. This increased resistance directly causes a drop in flow. The combination of a falling flow despite an increasing RPM is a classic sign of a post-pump obstruction.

Question 3

Which of the following clinical signs is the most specific indicator of an impending oxygenator failure due to plasma leak?

Accepted Answer

Frothy, pink-tinged fluid appearing in the oxygenator's gas exhaust port.

Answer

A plasma leak occurs when the integrity of the microporous membrane is compromised, allowing plasma and proteinaceous fluid to cross from the blood path into the gas path. This fluid mixes with the sweep gas and is expelled from the gas exhaust port, classically appearing as a frothy, pink-tinged exudate. This is a highly specific sign of this mode of oxygenator failure.

Question 4

A patient on VV ECMO requires Continuous Renal Replacement Therapy (CRRT). The CRRT circuit is initiated, drawing blood from a pre-pump access port and returning it post-oxygenator. Shortly after initiation, the ECMO circuit's pre-membrane (access) pressure becomes significantly more negative, and the venous line begins to chatter. What is the most probable cause?

Accepted Answer

The CRRT machine's ultrafiltration rate is too high, causing patient hypovolemia.

Answer

Aggressive fluid removal (ultrafiltration) by the CRRT machine can rapidly deplete the patient's circulating volume. This resulting hypovolemia leads to insufficient venous return to fill the ECMO circuit, causing the drainage cannula to suck against the vessel walls. This is manifested as an increasingly negative pre-membrane pressure and visible 'chatter' in the line.

Question 5

While assessing a patient on VA ECMO, a large bolus of air is accidentally introduced into the venous drainage line just before the pump. What is the most critical and immediate sequence of actions?

Accepted Answer

Clamp the arterial and venous lines, and take the patient completely off ECMO support.

Answer

The immediate, life-saving priority is to prevent the massive air bolus from being pumped to the patient, which would cause a catastrophic systemic air embolism. Clamping both lines and stopping the pump (taking the patient off support) isolates the circuit and contains the air. Subsequent steps would involve attempting to aspirate the air before cautiously resuming support.

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO - Extracorporeal Membrane Oxygenation Practice Test

ECMO - Extracorporeal Membrane Oxygenation Complications and Troubleshooting Questions and Answers