Somewhere between Stage 1 and Stage 2 the ECLS machine is brought to the bedside of the arresting patient and resuscitationist requests that the circuit is “primed”. Priming involves flooding the circuit with fluid – at this time we are currently using a balanced solution (Isolyte S), but that could change in the future.
The resuscitationist then takes the open cannula from the patient and the open tubing from the ECLS machine in each hand. Each conduit is topped off with saline, and the tubing is connected. This is done for both the arterial and venous cannulas. Once connected and secured, the pump can be turned on and the circuit is running.
A simulation of Stage 3 can be seen here:
And a real-life version here:
The ECLS Circuit Preparation
Hopefully, while you have been cannulating a primed circuit has been prepared. If not, you can do the prime yourself or for one of your colleagues using this ECMO circuit priming tutorial.
The portable ECLS unit is comprised of a centrifugal pump (Rotaflow, Maquet, Bridgewater, NJ), a heat exchanger (which can be used to warm or cool), and an oxygenator (Quadrox iD, Maquet, Bridgewater, NJ) that are heparin-lined (Bioline, Maquet, Bridgewater, NJ). These components reside on a portable cart that can be easily relocated to the ED.
While the resuscitationist is cannulating the femoral vessels, the critical care nursing team begins the process of priming the ECLS circuit. The ECLS components are filled with priming solution (Isolyte M, Braun Medical, Irvine, CA), which is anticoagulated with 2500 units of heparin. The patient is also systemically anticoagulated with 5000 units of heparin by IV push. Heparinization is optimized to a goal activated clotting time of 180 to 240 seconds. After de-airing the circuit (an important step to prevent air embolism), the tubing from the ECLS unit and the cannulas from the patient are ‘topped off’ with saline and the lines are then connected.
Once the bypass circuit is established, the system is able to optimize perfusion to the vital organs by providing a tissue perfusion pressure of greater than 40 mm Hg (mean arterial pressure minus central venous pressure) and maintaining a cardiac index over 2 L/min/m2. ECLS flow (measured in L/min) is estimated based on the patient’s body surface area. Adjustments to flow are guided by measuring continuous mixed venous oxygen saturation (SvO2) and mean arterial pressure monitoring, with a goal SvO2 of > 70% and MAP > 65 mm Hg. Adjustments to the sweep of the membrane oxygenator are guided by measuring patient carbon dioxide (PaCO2), with a goal of < 50 mm Hg.
Unless the patient’s condition is a contraindication, administer 5000 units of unfractionated heparin.
Attach the Circuit to the Cannulae
Put the end of each cannula next to the end of the circuit. Have a helper push a saline flush into both ends to fill any air left in either. Place circuit end into cannula. Push hard, if these separate badness ensues.
Secure the Cannulae
***BEFORE YOU DO ANYTHING ELSE: Use O-silk on a Keith needle to sew your lines in place. Secure them just like a chest tube using a wrapping technique. Do that now. If you forget, the shorter arterial line will fly out and your patient will exsanguinate in front of your eyes.