The choice of cannulas is fundamental for the ECMO to work optimally with as little complication as possible. There are a multitude of cannulas classified according to their internal diameter (in Fr, where 1 Fr = 1/3 mm), their length (mm) and their surface treatment.

They feature a contoured tip to facilitate penetration into the vessels (especially for the percutaneous approach), metal coils to strengthen the cannula and a rigid proximal portion with a connection fitting with the tubing. The term ‘admission cannula’ is used for venous drainage cannula and ‘reinfusion cannula’ for the cannula which carries oxygenated blood from the pump to the patient (inserted either in an artery or a vein, depending on which type of ECMO is used). Venous cannulas are usually wider and longer than arterial cannulas.

In ECMO, we use centrifugal pumps. These are non-occlusive pumps which operate on the principle of entraining blood into the pump by means of a vortexing action of spinning impeller blades or rotating cones. The impellers or cones are magnetically coupled with an electric motor and, when rotated rapidly, generate a pressure differential that causes the movement of blood. The flow rate is calculated (by ultrasonic sensor) in L/min. The console allows the display and setting of various parameters of ECMO (flow, high- and low-flow alarms).

The centrifugal pump generates less haemolysis than other types of pump, and the pump stops in case of air embolism in the circuit; the rate depends mostly on input (blood volume and the choice of cannula size) and output pressure (vascular resistance). Centrifugal pumps are non-occlusive, which means that the blood can move in one direction or the other. Therefore, there can be a backflow with the patient’s blood going back to the pump. This is seen most often when the ECMO rates are low and the pressure generated by the patient’s heart is more important. There is an anti-backflow system on pumps, but regular monitoring is essential, and the golden rule is to clamp the arterial line whenever the pump is not running. All pumps are equipped with an emergency hand crank to compensate for a pump-operating failure.

The circuit is composed of PVC tubes with an internal diameter of 3/8 inch (9.525 mm) packaged sterilely with a debubbling pocket. The circuit has a surface treatment in order to reduce clotting.

The blood passes through polypropylene fibres that allow gas exchange to provide oxygenation and decarboxylation. The oxygenator reproduces the alveolar capillary function. Modern oxygenators are composed of multiple hollow fibres of <0.5 mm diameter, coated with a hydrophobic polymer (polymethylpentene), allowing the passage of gas (partial pressure gradient) but not liquid (Fig. 1.2). The gas flows inside the fibres, and the liquid is on the outside. Compared with a healthy lung, transfer capacities with the membrane (artificial lung) are more than ten times lower (3000 vs. 200–250 mL/min). These transfers of O₂ and CO₂ capacity are determined by the exchange surface and the pore diameter of the fibres. These elements are not editable at the bedside to modify these exchanges; the action focuses on the flow of liquid (pump rate) and gas intake.

This is a miniaturised thermal unit that can heat patient blood by convection. The thermal unit can heat up the patient’s blood during the passage of the latter through the oxygenator: hot water circulates around the oxygenator and thus indirectly warms the patient’s blood. The introduction and removal of the device is performed by the perfusionist.