Over the last two years, Extracorporeal Membrane Oxygenation (ECMO) has emerged as a therapy for COVID-related Acute Respiratory Distress Syndrome (ARDS) and continues to be a successful therapy for ARDS cases caused by other illnesses.

However, the effectiveness of ECMO therapy diminishes if reinfused oxygenated blood is recirculated by the drainage cannula instead of being delivered to the patient. According to the Extracorporeal Life Saving Organization (ELSO), the clinical significance of recirculation is determined by the patient’s dependence on ECMO oxygenation. Significant recirculation can cause dangerously low oxygen levels even if the ECMO circuit is functioning properly.

Recirculation is a common complication during veno-venous (VV) ECMO and knowing the signs of recirculation is key, but recirculation must be quantified to understand its effect on the patient. When recirculation is quantified, it can be controlled, and controlling recirculation can improve patient therapy, optimize oxygen delivery, and enhance success at weaning the patient off ECMO.

Measuring the amount of recirculation during ECMO can provide vital information about the patient’s health and the performance of the ECMO circuit.

Quantifying recirculation helps:

• Establish optimal pump settings
• Identify cannula migration
• Identify restricted flow due to hypovolemia and/or cardiac failure

Identify the cause of recirculation

Several factors influence VV ECMO recirculation. 

Cannula positioning or configuration: When the drainage and reinfusion cannulae are close together, the likelihood of recirculation increases. Changes in the patient’s position can also affect recirculation.

Pump speed, cannula size, extracorporeal blood flow: An increase in pump speed and ECMO blood flow rate has been shown to correlate with recirculation.

Changes in pressure: Changes in intra-abdominal, intrathoracic or intra-cardiac pressures can increase recirculation.

Recognizing and calculating recirculation

Often, the first sign of recirculation in a patient is a pulse ox reading that dips below 86%. The patient may also have an increasing pre-oxygenator 02 saturation. You can quantify recirculation rates using the following equation, according to ELSO.

Recirculation (%) = (SpreO2 – SvO2)/(SpostO2 – SvO2) x100

Technology for mitigating recirculation

The Transonic ELSA monitor provides vital information because it:

• Measures true blood flow in ECMO circuits
• Quantifies recirculation during VV ECMO
• Detects and trends oxygenator clotting

Using the ELSA, a perfusionist or intensivist can identify and correct excessive recirculation. Values can be obtained within 3 minutes, and knowing the values for both flow and recirculation can reduce the time the patient has to spend on ECMO.

Want to see ELSA in action? Request a demo today.