ECMO Machine

Overview

ECMO, extracorporeal membrane oxygenation, is prolonged life support for patients whose lungs, heart, or both have failed beyond what a ventilator and drugs can manage. Blood is continuously drained from a large vein, pumped through an artificial lung that adds oxygen and removes carbon dioxide, warmed back to body temperature, and returned to the patient. Unlike a heart-lung machine, which supports a few hours of surgery, an ECMO circuit runs for days or weeks at the bedside while the patient's own organs recover.

Two configurations exist. Veno-venous ECMO drains and returns blood to the venous system and supports only gas exchange, used for severe respiratory failure such as ARDS. Veno-arterial ECMO returns blood to an artery and so also provides circulatory support for cardiac failure or cardiac arrest. The permanent hardware is the Control Console, Centrifugal Pump Drive, and Heater Unit; the blood-contacting Disposable Circuit and Membrane Oxygenator are single-use.

The pump

Modern ECMO uses a Centrifugal Pump Drive built around a disposable Disposable Centrifugal Pump Head whose impeller is spun magnetically by the Drive Magnet Plate, with no shaft seal touching the blood. Centrifugal pumps are preferred over roller pumps for long runs because they are pressure-limited: if the return line is occluded the head simply recirculates instead of generating the destructive pressures a roller pump would. Flow depends on both impeller speed, set on the Pump Speed Knob up to 5,000 rpm, and the downstream resistance, so it is always measured directly rather than inferred. The pump head's pivot or magnetic bearing minimises stagnation zones that would otherwise seed clotting, and an Emergency Hand Drive hand crank allows manual pumping if power and battery both fail.

The artificial lung

Gas exchange happens in the Membrane Oxygenator. Its PMP Hollow-Fiber Bundle is a mat of polymethylpentene (PMP) hollow fibers with a surface area near 1.8 m². Sweep gas flows inside the fibers while blood flows around the outside, the two separated by the diffusion membrane. PMP is non-porous, so unlike older microporous polypropylene it resists plasma leakage and supports the long run times ECMO demands. Oxygen diffuses into the blood and carbon dioxide diffuses out; the Potting Headers seal the fiber ends to keep gas and blood compartments separate, and an Integrated Heat Exchanger in the same housing tempers the blood.

Oxygenation and CO2 removal are controlled independently. The Sweep Gas Supply sets oxygen concentration with the Gas Blender, which governs how much oxygen the blood picks up, while the Sweep Gas Flowmeter sets total sweep flow, which, like minute ventilation in a real lung, governs CO2 clearance. The two are adjusted separately to target blood gases.

Temperature control

The Heater Unit circulates distilled water from the Water Tank through the oxygenator's heat exchanger at 33–39 °C. Because the extracorporeal circuit exposes a large blood volume to room air, the patient would otherwise cool steadily, so active warming holds normothermia. The Heater Controller uses dual independent sensors and a Thermal Fuse hard cutout to prevent the blood ever being overheated.

Monitoring and safety

The Sensor Suite clips non-invasively onto the circuit. An ultrasonic Ultrasonic Flow Sensor confirms delivered flow, the Bubble Sensor guards the return line against air embolism, and three Pressure Sensor channels monitor drainage suction and the pressure drop across the oxygenator, a rising gradient warns of clot forming in the membrane. An optical Venous Saturation Sensor reads venous oxygen saturation, a direct measure of whether support is meeting the patient's oxygen demand. Throughout the run the patient is anticoagulated with heparin titrated to clotting time, because the large foreign surface of the circuit otherwise triggers thrombosis.

Circuit and console

The Disposable Circuit uses heparin- or phosphorylcholine-coated Coated Tubing Set tubing kept deliberately short to limit the roughly 600 mL prime volume. Large Drainage Cannula and Return Cannula cannulae, sized 15–29 French, connect to the patient's great vessels, with Pigtail Access Ports for sampling and infusion. The Control Console runs the pump and safety logic on separate processors, drives the LCD Panel display and audible alarms, and carries a 12 V Battery with a BMS Board giving at least 90 minutes of support, enough for the whole circuit to move on the Transport Cart between the ICU, imaging, and even a transport vehicle.