An infusion is the administration of a fluid into the human body bypassing the gastrointestinal system (“parenterally”), usually into a vein. The route of access via an infusion is chosen either because the substance in question cannot be administered in any other way or because of factors affecting the patient, such as dysphagia.
What is an infusion?
An infusion is the administration of a fluid into the human body bypassing the gastrointestinal system (“parenterally”), usually into a vein. An infusion is said to occur when the delivery is prolonged. While the patient is sitting or lying down, the substance is administered either by gravity via an infusion bottle or by a mechanical infusion pump. This is to be distinguished from an injection, in which the active substance is introduced into the patient’s body within a short period of time, for example, by means of muscle force through pressure on the plunger of an injection syringe. Intravenous access is predominantly chosen for infusions, i.e. the fluid is introduced directly into a vein. Other common access routes include subcutaneous (under the skin) or intraosseous (into the medullary cavity of a bone) infusion.
Function, effect, and goals
Infusion of fluids is required when absorption through the gastrointestinal tract is not possible. This may be because the substance in question is not suitable in principle for absorption via a mucosal route. Another reason may be that the patient in question, due to his or her illness, is unable to take a drug that could in principle also be swallowed by this route. The most commonly used route for an infusion is the intravenous route, in which the fluid is introduced into a vein, through which it travels to the heart and from there throughout the body. The infusion can be administered either through a metal cannula or through a flexible indwelling venous cannula that is inserted into a superficial vein, typically in the hand or arm. If drugs are to be administered that easily irritate these superficial veins, or if a suitable vein cannot be located, the infusion may be made into one of the central veins in the neck, under the collarbone, or in the groin. This is then referred to as a central venous catheter (CVC). A special form is a port catheter, in which a tube is surgically inserted into a central vein and connected to a chamber that is implanted under the skin. By piercing the skin and a membrane on this chamber with a special needle, a patient can thus easily be infused again and again via a central venous access. Such a port catheter is often used, for example, for the infusion of chemotherapy drugs in patients with cancer. For some purposes, such as infusing fluids in patients who cannot drink adequately, a subcutaneous infusion route may also be chosen. In this case, a fine needle is inserted into the fatty tissue under the skin. The advantage of this method is that no vein needs to be found. The disadvantage is that the fluid is absorbed slowly by the subcutaneous fatty tissue into the vascular system and that some drugs are not suitable for such a subcutaneous infusion. In emergency situations, if parenteral drug administration is required but no vein can be found, an intraosseous infusion can also be administered, for which a robust needle is inserted into the bone marrow cavity of, for example, the lower leg bone.
Risks and hazards
Infusion carries several risks. If air accidentally enters the vascular system, it can lead to a life-threatening air embolism. There is also a danger if fluids that are not suitable for intravenous infusion are applied this way. Finally, any substance introduced into the body can trigger an allergy, which can be particularly pronounced with parenteral infusion. If the access slips out of the vein, the infusion may enter the surrounding tissue instead of the vein, which can lead to severe soft tissue damage with some drugs. Finally, complications can arise when the access is created.For example, a typical complication of placing a CVC for an infusion is injury to the lung from the puncture needle, which can lead to pulmonary collapse (“pneumothorax“).
