Measuring Oxygenator Blood Volume During ECMO

Oxygenator blood volume (OXBV) measurements are one more tool for healthcare providers of critically ill patients on extracorporeal life support. It’s a measurement that doesn’t always get the attention it deserves, though.

Now, you may be thinking that an oxygenator has a standard volume. That is true: a 500 mL oxygenator is exactly that, half a liter. So, why measure its volume? OXBV is a proxy measurement for the clot burden in the oxygenator. It’s one of many clinically relevant data points that help perfusionists, specialists and the entire ECMO team make informed decisions. Monitoring OXBV trends alongside other ECMO parameters can contribute to a more complete understanding of the patient’s needs.

What exactly is OXBV?

In a nutshell, it’s the total amount of blood that flows through the oxygenator compartment, per unit time, during extracorporeal membrane oxygenation (ECMO).

Benefits of Measuring OXBV

We can’t talk about the benefits of measuring OXBV without mentioning the reality of clotting in the oxygenator. Clotting of the circuit is one of the major complications of ECMO. And the patient’s blood starts clotting to some degree or another as soon as ECMO therapy begins.

ECMO care teams have to balance opposing challenges: anticoagulant levels must be high enough to maintain blood flow and minimize circuit clot formation, yet low enough not to induce excessive bleeding.

When clots become an unmanageable concern, the patient will require an oxygenator change (or potentially a full circuit replacement). Cascading or other issues, such as leaks in the ECMO circuit, can also lead to emergent change-outs.

In fact, a recent study found just how common circuit replacements are in ECMO patients.

18%

of patients overall required a circuit change

31%

of patients on ECMO for more than seven days needed a change-out

33%

of those change-outs were due to clotting

Acute oxygenator thrombosis (that is, when the clotting has reached a critical stage) can lead to an emergency change-out – a situation to avoid whenever possible for the sake of both the patient and the care team.

And that’s where OXBV measurements come in.

OXBV, the amount of blood moving through the oxygenator, decreases as clots form within the oxygenator. While no single OXBV measurement by itself tells the full story, the baseline and trending data can support decisions about anticoagulation treatments and oxygenator change-outs.

Waiting for a patient to decompensate as a sign that the oxygenator needs to change is like waiting for the smoke alarm to determine when dinner is ready. Instead, looking at trending data – including OXBV measurements – can support proactive clinical decision-making.

Measuring OXBV gives care teams:

The ability to assess the “true volume” flow through the oxygenator, and thus oxygenator efficiency, via trending data.
Information that can be used to inform patient treatment, including anticoagulation decisions.
An expanded window of opportunity to proactively perform an oxygenator exchange, preventing emergency change-outs.

This, in turn, benefits hospital administrators as well. OXBV data-driven decision-making can help avoid unnecessary or premature change-outs of expensive oxygenators, while also leading to better allocation of resources and staffing during semi-elective exchanges

How Do You Accurately Measure OXBV?

OXBV can be measured with the Transonic ELSA monitor, which uses ultrasound dilution technology to provide the right data at the right time.

ELSA’s measurements come from the transit time of a saline bolus passing through the oxygenator as recorded by a sensor placed after the oxygenator. That is, when a saline bolus is injected upstream from the oxygenator, the time the indicator takes to travel through the oxygenator is directly proportional to blood volume.

How the Transonic ELSA Monitor Works

The ELSA is a stand-alone ECMO FlowMeter that’s portable, user-friendly and easy to clean. The monitor is battery-powered and can be pole-mounted for mobility, facilitating access to critical bedside data.

The clamp-on sensors, which are noninvasive, transmit ultrasound waves through the blood line. The ELSA Monitor measures the wave’s phase shift in order to provide a measurement of volume flow.

To measure OXBV, normal saline is introduced upstream from the oxygenator. The bolus passes the arterial sensor, providing information about the volume of flow through the oxygenator. OXBV trending graphs are available directly on the ELSA for easy tracking of volume changes indicative of clot formation, giving critical care intensivists, perfusionists and the ECMO team the right data when they need it.

Schedule ELSA Demo