A heart lung machine is a piece of medical equipment which is designed to take over the function of the heart and lungs during surgery so that a surgeon can operate in a relatively bloodless field on a heart which is not moving. Although this may sound fairly simple, heart lung machines are actually very complex, and it took a great deal of trial and error to develop an effective machine which would address issues like bubbles in the blood, body temperature, and clotting.
The earliest heart lung machines were developed in the 1950s. The technology involves inserting cannulas to divert the blood from the heart to the heart lung machine. As the blood passes through the machine, it is oxygenated and then pumped back into the body. This process is known as cardiopulmonary bypass or simply bypass. Once the surgery is complete, the patient can be taken off bypass to allow the heart and lungs to return to their regular duties.
Heart lung machines can use bubble oxygenation or membrane oxygenation to oxygenate the blood, depending on the design. The device moves the blood through tubes with the use of rollers which put pressure on the tubes, rather than a mechanical pump, to avoid creating bubbles which could injure or kill the patient. The patient must also be given a blood thinner to prevent clotting, as the blood can react with the materials in the tubes and clump up.
The heart lung machine is run by an allied health professional known as a perfusionist. The perfusionist is responsible for setting up the equipment properly, monitoring the patient while he or she is on bypass, and alerting the surgeon to any problems which emerge. The development of the heart lung machine brought about a revolution in open heart surgery, as surgeons found their repertoires radically expanded. Defects and injuries which would have been impossible to repair became routine fixes, and many lives were saved as a result.
A related concept, extracorporeal membrane oxygenation (ECMO) involves the use of a machine similar to a heart lung machine to take over for damaged hearts and or lungs. This is most commonly seen in intensive care units, and is designed to provide support while the body heals, with the patient eventually being taken off ECMO. Patients with damage which has progressed so far that the hearts and lungs will never be able to function are candidates for transplant, who may use ECMO while they wait for a donor organ to become available.