A perfusion machine is a specialized medical device designed to temporarily maintain the body’s essential life functions when natural systems are intentionally halted or bypassed. It operates as an external support system, circulating and oxygenating blood to ensure tissues and organs continue to receive the necessary supply of nutrients and gas exchange. This technology allows surgeons to perform highly intricate procedures on organs that require a still, bloodless field.
What Perfusion Machines Accomplish
The most frequent application of a perfusion machine is in Cardiopulmonary Bypass (CPB), often called the heart-lung machine. When surgeons operate directly on the heart, such as during a coronary artery bypass graft or valve repair, the heart must be stopped to create the necessary surgical environment. The perfusion machine takes over the functions of both the heart and the lungs during this period.
The machine establishes an extracorporeal circuit, channeling blood away from the heart and lungs and through the machine before returning it to the body. Deoxygenated blood drains from the patient’s major veins into the circuit’s reservoir. Once circulation and gas exchange are supported, a cardioplegia solution—a high-potassium fluid—is administered to safely and temporarily stop the heart’s electrical activity. This controlled cessation ensures the surgical team has a stable, motion-free field.
Key Components and How They Function
The function of a perfusion machine relies on three main components: the pump, the oxygenator, and the heat exchanger.
The Pump
The pump acts as the artificial heart, generating the flow and pressure needed to circulate blood throughout the body. Two common pump designs are used: the roller pump and the centrifugal pump. The roller pump works by compressing a segment of the tubing against a raceway, mechanically pushing the blood forward in a controlled, non-pulsatile flow. The centrifugal pump uses rapidly rotating cones to propel the blood via centrifugal force. This design avoids over-pressurizing the system but requires a separate flow meter to verify the output.
The Oxygenator
The oxygenator functions as the artificial lung, facilitating gas exchange. Blood from the patient is spread across a large surface area of thin, porous membranes, where it is exposed to oxygen gas. This process removes carbon dioxide from the blood while simultaneously adding fresh oxygen, making the blood ready for return to the body.
The Heat Exchanger
Integrated into the circuit is a heat exchanger, which manages the patient’s body temperature. This device can cool the blood to induce systemic hypothermia, which reduces the metabolic demands of the body’s tissues, offering protection during reduced circulation. Conversely, it can rewarm the blood before the patient is weaned off the circuit and the heart is restarted.
Use in Organ Preservation for Transplantation
Beyond the surgical suite, specialized perfusion machines are used in preserving donor organs for transplantation, known as machine perfusion (MP). This technique represents an advancement over the traditional method of static cold storage (SCS), which simply slows the organ’s metabolism by chilling it. Machine perfusion actively pumps a specialized solution, often oxygenated, through the organ’s vasculature, extending its viability outside the body.
This dynamic preservation method is categorized by the temperature of the perfusate. Hypothermic machine perfusion (HMP), typically conducted at temperatures below 12°C, slows cellular processes and reduces metabolic demand, which is particularly beneficial for kidney preservation. Normothermic machine perfusion (NMP), which maintains the organ at near-body temperature (around 37°C), allows for continuous metabolic activity and has proven effective for liver and lung preservation. A key advantage of MP is the ability to assess and condition the organ before transplantation. By monitoring parameters like fluid dynamics, bile production, and oxygen consumption during perfusion, the viability of the organ can be better determined, improving the success rate of the transplant and allowing for the safe use of organs that might otherwise have been discarded.
The Role of the Clinical Perfusionist
The complex machinery and intricate physiological processes of the perfusion circuit require a highly trained operator, known as a clinical perfusionist. The perfusionist is a specialized healthcare professional responsible for setting up, operating, and managing the entire extracorporeal circulation system during surgery. They work in tandem with the surgeon and anesthesiologist, monitoring the patient’s physiological status throughout the procedure.
A perfusionist’s duties include continuously monitoring and adjusting blood flow rates, regulating gas levels within the oxygenator, and administering medications, such as blood thinners like heparin to prevent clotting. They also manage the patient’s blood chemistry, including electrolyte levels and acid-base balance, responding to any changes in the patient’s condition. Their expertise ensures that the patient’s tissues remain adequately perfused and oxygenated while the heart and lungs are temporarily non-functional.