Contrast enhanced CT during extracorporeal membrane oxygenation

Contrast-enhanced CT examinations 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 ECMO

As venovenous ECMO is often seen in patients with respiratory failure ¹ the cardiocirculatory output is somewhat normal and therefore exams tend to similar to standard exams with the curveball of administering the contrast via ECMO.

• contrast delivery
  • V-V ECMO examinations require the contrast to be injected via the oxygenator inlet 
• ECMO flow
  • flow can be maintained during the examination as this will not impact the contrast intake

Venoarterial ECMO

Parenchymal enhancement study

• contrast delivery
  • venoarterial ECMO examinations that strive to achieve parenchymal enhancement can receive contrast via the oxygenator inlet 
• ECMO flow
  • ECMO can be left at full flow 

Venoarterial ECMO with a carotid cannula (CTA)

• contrast delivery
  •  contrast via the oxygenator inlet 
  • the injection can also be conducted via a central venous line
• 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.

• 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
• 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.

• contrast delivery
  • central venous line
• ECMO flow
  • the ECMO flow needs to be reduced (if possible) 

Venoarterial ECMO Radiographic pitfalls

• pseudo-filling 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