Modern cannulas are strong and thin walled and made of biocompatible silicone-polyurethane which is malleable at body temperature, aiding insertion. They are sometimes coated with additional polymers to reduce platelet activation and triggering of the inflammatory cascade. However, no coating to date has been proved to eliminate the well-known risk of bleeding and coagulopathy associated with circuit exposure. The cannulas are also reinforced with stainless steel to reduce the risk of kinking and collapsing (with subsequent ECMO flow interruption) sometimes caused by high suction pressures.
The drainage cannula allows blood to flow through the pump to the oxygenator. They are typically 7.5 to 10mm in diameter and are configured with multiple holes on the sides to optimize suctioning of blood from the circulation. They are normally sited in large central veins such as the inferior vena cava via the femoral vein or the superior vena cava. The tip should be sited at the border between the right atrium and superior vena cava to minimize the risk of recirculation in V-V ECMO.
The return cannula returns blood from the oxygenator to the patient. They are typically 5 to 6.5mm for V-A ECMO or 7 to 7.5mm for V-V ECMO. They are sited in either the right atrium (for V-V ECMO) or the femoral artery with the tip either in the iliac artery or in the distal abdominal aorta (for V-A ECMO).
Chan Ching Wen Hazel