Do the terms “sweep” and “chatter” set you on edge?Uncertain how to interpret the countless monitors and labs for your patients on ECMO? Join us in a collaboration with the PedsCrit Podcast, as our guest, Dr. Karen Fauman, Pediatric Intensivist, Pediatric ECMO Medical Director, Director of Pediatric Palliative Care, Program Director of the PICU Fellowship at Comer Children’s Hospital, and ECMO Enthusiast, breaks down the basics of ECMO care! Listen as she outlines everything you need to know, from oxygen delivery to circuit liberation.
ECMO, or extra-corporeal membrane oxygenation, is a form of life support in which venous blood is removed from a patient, gets oxygenated, CO2 is removed, and then is returned to the patient. The oxygenated blood is either returned to the venous system (VV ECMO), or arterial system (VA ECMO). It is used for refractory respiratory or hemodynamic failure, or both. Some indications include myocarditis, post-operative congenital heart disease, septic shock, toxic ingestions, congenital diaphragmatic hernia, pneumonia, pulmonary hypertension, and ARDS.
Understanding ECMO requires an understanding of oxygen delivery, which is dependent on cardiac output and the oxygen content of the blood, or:
Oxygen delivery = (SV x HR) x (Hgb x SaO2 x 1.34) + (PaO2 x 0.003)
This equation can be difficult to conceptualize, so Dr. Fauman teaches using a metaphor for oxygen delivery:
Imagine that that there is a kingdom made up of a series of villages (the body and its organs). These villages are all connected by a train system (the cardiovascular system). The villagers (cells) only eat potatoes (hemoglobin bound oxygen, or O2), which must be delivered to them. There is a main train station (the heart) that sends out a train (blood) with many train cars (hemoglobin), and when the kingdom is enjoying good times these train cars are filled to the brim with potatoes (oxygen-bound-hemoglobin). In order to keep the kingdom happy, the train must return to the station with a surplus of potatoes, about 75-80% of the original cargo (aka central venous O2 saturation). If the surplus begins dropping then the main station has to figure out how to get more potatoes delivered.
If you have a patient who – despite loading up the train cars with extra potatoes (increasing oxygen saturation), increasing its speed (vasoactives) and adding more train cars (hemoglobin), has a dwindling surplus upon arrival to back to the train station (SvO2 ~50-60% and lower) they are in shock and may need ECMO.
There are a variety of variations of the ECMO circuit, but they all consist of:
ECMO Parameters and Pressure Monitors
While the criteria for ECMO utility may be hotly debated, Dr. Fauman outlines some generally agreed upon criteria for “good candidates,” meaning they are likely to be liberated from ECMO and do well. These include: patients with a reversible condition, no other underlying medical conditions, organ failure limited to cardiac and respiratory system, an intact immune system, and an expected course of less than a few weeks. There are some limitations based on size (tends not to be available if infants are less than 1.8 kg or less than 34 weeks post-conceptual age due to risk of IVH).
ECMO is appropriate when the patient is unable to be supported from a hemodynamic standpoint – when despite multiple vasopressors they are unable to maintain the body’s metabolic demands1.
Historically the oxygenation index (OI) has been used to determine severity of respiratory failure and potential need for ECMO. Typically, VV ECMO is considered as the OI approaches 40 despite optimal ventilator management; this value is generally used to determine initiation in infants and small children.
While caring for a patient on ECMO, Dr. Fauman notes that there are three of blood gases that are of particular importance.
Other considerations include:
Dr. Fauman notes that one of the more challenging parts of caring for these patients is waiting. It is difficult, but crucial, to wait (and wait and wait) to allow the lungs and heart to rest.
So, when do you know it’s time to move toward liberation?
Cardiac recovery can be tracked by a few markers. Things to watch for include increasing pulsatility of the arterial waveform (ex. pulse pressure increasing from 10 to 30), improved cardiac squeeze on echo as flows are weaned, normalization of lactate, and tolerating movement or physical therapy without drops in SvO2. When these signs of recovery are present it is reasonable to trial weaning the flow (not too low or the circuit will clot). If the patient tolerates this without significant changes in hemodynamics or lactate, then perform a clamp trial. Have pressors and calcium on hand, wean the flow off and clamp the circuit (typically with the patient sedated) for up to an hour. Then decide if they are ready for decannulation based on the amount of vasoactive support needed, in addition to other markers (ex., lactate and SvO2) during this trial.
Patients cannulated for respiratory failure will typically have chest x-rays (CXR) that have completely whited out lung fields. The first sign of recovery on CXR is the appearance of air bronchograms. Dr. Fauman likens these growing branches to A Tree Grows in Brooklyn2, signifying little branches of hope. As these air bronchograms grow, it is reasonable to gently trial recruitment strategies (manual bagging, gently increasing vent settings). It is only appropriate to continue if there are signs of improved compliance, sometimes over days to weeks. In order to liberate, respiratory recovery should be represented by evidence of a tidal volume (4-6cc/kg) on rest or extubatable settings, decreasing sweep, tolerating physical therapy, and low ventilator FiO2 (expert opinion of no more than 50%). No clamping trial is needed, but the sweep may be left off for up to and even longer than 24hrs.
Many patients do very well after ECMO. Patients who tend to do less well are those who do not fit the above listed criteria. For example, oncology patients who don’t have a functioning immune system, have active disease, or were cannulated in the setting of an infection that is unlikely to clear tend to have worse outcomes.
Listeners will understand the basics of the ECMO circuit, indications for VV and VA ECMO, and the steps in initiation, management and liberation.
After listening to this episode listeners will…
Dr Fauman reports no relevant financial disclosures. The Cribsiders report no relevant financial disclosures.
Hodges Z, Fauman K, Shanklin A, Masur S, Chiu C, Berk J. “#79: ECMO Essentials with PedsCrit – It’s All Trains and Potatoes”. The Cribsiders Pediatric Podcast. https:/www.thecribsiders.com/ March 1, 2023.
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