Contrast-enhanced CT of patients undergoing extracorporeal membrane oxygenation (ECMO) presents unique technical and diagnostic challenges.
Technical considerations
There are a number of factors that need to be considered to ensure contrast-enhanced CT studies of ECMO patients are both successful and safe. The complexity of the study is dependent on the type of ECMO the patient is receiving, the examination requested, and the stability of the patient.
Transfer times from the ward to CT and back can be up to 80 minutes given the complexity of the logistics and examination 1.
NB: This article is intended to outline some general principles of protocol design from current literature 1-4. The specifics will vary, each department will have stringent well-written guidelines to ensure these examinations are completed safely in accordance with local policy.
Venovenous (VV) ECMO
As venovenous ECMO is used in patients with respiratory failure 1. Cardiocirculatory output is somewhat normal and therefore exams tend to be similar to standard exams with the added issue of contrast administering the via ECMO catheters.
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contrast delivery
VV ECMO examinations require the contrast to be injected via the oxygenator inlet
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ECMO flow
flow can be maintained during the examination as this will not impact the contrast intake
Venoarterial (VA) ECMO
Parenchymal enhancement study
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contrast delivery
VA ECMO examinations that strive to achieve parenchymal enhancement can receive contrast via the oxygenator inlet
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ECMO flow
ECMO can be left at full flow
Venoarterial ECMO with a carotid cannula (CTA)
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contrast delivery
contrast via the oxygenator inlet
the injection can also be conducted via a central venous line
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ECMO flow
for oxygenator inlet, ECMO can be left at full flow
for central venous line, flow needs to be decreased
Venoarterial ECMO with femoral artery cannula (CTA)
This requires a retrograde fill of the aorta and can be quite challenging for both the radiographer to perform and the radiologist to interpret.
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contrast delivery
for abdominal CTA examinations contrast via the oxygenator inlet
for thoracic CTA examinations most often a central venous line is utilized
injection can also be conducted via a central venous line
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ECMO flow
the ECMO pump can be left at full flow or even higher for oxygenator inlet injections 2
the ECMO pump is often reduced for CTA thoracic exams via a central venous line 2
CT pulmonary angiogram
Venoarterial ECMO is a bypass of the entire cardiopulmonary system, one must use a central venous line.
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contrast delivery
central venous line
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ECMO flow
the ECMO flow needs to be reduced (if possible)
Venoarterial ECMO radiographic pitfalls
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pseudofilling defects
partially opacified aorta may be due to an early phase examination due to retrograde filling 1
there are cases (left heart failure) where the left heart does not enhance at all 1