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PCRTO (pump controlled retrograde flow trial off)

A novel technique for trail off from VA ECMO in paediatric and neonatal ECMO patients

In the Heartlink ECMO centre in Leicester, we have developed a novel technique for trial off from VA ECMO in neonatal and paediatric patients.

Trial off Veno Arterial Extracorporeal Membrane oxygenation (VA-ECMO) is the process used to assess whether or not the patient can sustain lung or cardiac function (or both) without mechanical support. Classically this involves sudden separation of the circuit from the patient by clamping both cannulae, the interposition of an Arterio-Venous bridge (if not already installed) to allow ECMO circuit recirculation and maintenance of anticoagulation to avoid clotting. This process introduces areas of stagnant blood within the circuit with the subsequent risk of clot formation. Clot formation can hamper the reinstitution of ECMO should the trial off prove unsuccessful and risks propagation of clot into the patient. In our institution we felt this method provided a maximum VA trail off time of 2hrs before risk of clot formation and loss of circuit integrity, preventing safe reinstitution of ECMO support in patients who are not ready to come off ECMO
Our novel technique, Pump Controlled Retrograde Trial Off (PCRTO) relies on retrograde flow to maintain circuit integrity and allows a longer trial off from VA ECMO support without circuit clot formation or significant patient haemodynamic compromise. This technique avoids the insertion of an arterio-venous bridge and the need to clamp the circuit. We use this technique routinely during trial off from VA ECMO in all our neonatal and paediatric patients, and it had been adopted and implemented across ECMO centres internationally.

PCTRO Technique

In Heartlink ECMO Centre, Leicester, VA-ECMO is established by neck cannulation (utilising the right common carotid artery and right internal jugular vein). The cannulae are connected to the circuit which comprises a Thoratec Pedi-VAS centrifugal pump and a Medos Hi-lite 800 LT oxygenator.
In PCRTO appropriate mechanical ventilation is established based on the lung mechanics of the child. The sweep gas is disconnected and the trial off is commenced.
At the start of the trial off the flow probe is reversed and the pump revolutions per minute (RPM) is reduced. As the pressure generated by the pump falls below the systemic arterial pressure a state of retrograde flow is induced. The RPM is further reduced until a retrograde flow of around 120 mls/min is achieved. The pump is acting as a brake to stop excessive retrograde flow with systemic steal of blood and the risk of increased pulmonary blood flow. Activated clotting time (ACT) is kept between 200-220 seconds
By removing the bridge completely and relying on retrograde flow to maintain circuit integrity a long trial off from ECMO support (up to 5hrs in our published data (RE)) can be achieved without significant haemodynamic compromise, and reduced risk of clot propagation.
There are some patients in whom, even using the 'brake'to minimise excessive systemic steal, the afterload reduction is too much and require vasopressors for the duration of the trial off. Our experience shows that in these patients the vasopressors can be stopped when the patient is fully separated from ECMO support at decannulation. We have not seen evidence of haemolysis related to blood flow against the direction of the centrifugal pump, or complications related to microemboli entering the patient on the venous side during retrograde flow.

Reference:

Pump Controlled retrograde Trial off from VA ECMO
Westrope C, Harvey C, Robinson S, Speggiorin S, Faulkner G, Peek
GJASAIO J 2013 Sept 59 (5) 517-519

 

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