Contraindication
Emergencies that require connection to a heart–lung machine often do not provide the time to evaluate the patient’s medical history. The heart–lung machine is an extreme situation for the body, but often the only chance for the person concerned. Although the risk is considerable, failure to do so can cost many people their lives. The risk-benefit ratio, which also takes into account other previous illnesses and the patient’s general condition, must be carefully considered when planning interventions.
Risks and side effects
A heart surgery is by nature a major intervention, and carries a number of risks. In addition to the “usual” risks that arise during an operation, there is also the risk of microembolization when using the heart-lung machine: microscopic particles detach from the device or from the vessel wall, coagulate (i.e. clot), and block the device or vessels in the patient. Therefore, filters and anticoagulants are always used.
Although the latter make the patient’s blood more fluid and less susceptible to clotting, they also cause problems for the surgeon, as bleeding is logically more difficult to stop. This is where fine tuning is required. an oxygen deficiency.
While the lung with its billions of pulmonary alveoli provides a total surface area of almost 200m2 for oxygen enrichment of the blood, in a heart-lung machine it is only 2-10m2 . The diffusion area where blood and oxygen come into contact is therefore much smaller, and the oxygenation function of the lung is only incompletely replaced. An immune reaction.Since hoses and devices are foreign to the body, the latter reacts with an immune response to the supposedly harmful components in its circulation.
Signalling substances are released to fight the disease, which can lead to an inflammatory reaction and, in an emergency, to death.
- Microembolization: Microscopically small particles detach from the device or from the vessel wall, coagulate (i.e. clump), and clog the device or vessels in the patient. Therefore, filters and anticoagulants are always used.
Although the latter make the patient’s blood more fluid and less susceptible to clotting, they also cause problems for the surgeon, as bleeding is logically more difficult to stop. So this is where fine tuning is required.
- An oxygen deficiency. While the lung with its billions of pulmonary alveoli provides a total surface area of almost 200m2 for oxygen enrichment of the blood, in a heart-lung machine it is only 2-10m2 due to its design.
The diffusion area where blood and oxygen come into contact is therefore much smaller, and the oxygenation function of the lung is only incompletely replaced.
- An immune reaction. Since hoses and devices are foreign to the body, it reacts with an immune response to the supposedly harmful components in its circulation. Signalling substances are released to fight the disease, which can lead to an inflammatory reaction and, in an emergency, to death.
- The edema formation.
Due to the pressure between blood and tissue, more water flows from the vessels into the surrounding tissue – the blood thickens and the tissue swells. One speaks of oedemas. After the operation, patients are very edematous, i.e. they have a lot of water in their legs and arms. Only after the operation has been completed can the body remove the water from the tissue and send it back into the blood – which suddenly forms too much volume. So the kidneys have to excrete the excess water from the blood (similar to a dryer that spins wet clothes to remove the water from them), which is especially problematic in patients with renal insufficiency.
