Intravenous therapy, commonly known as IV therapy, is known as the administration of a liquid substance directly into a vein. It is also known as drip therapy, because most often the liquid is suspended above the IV site by an infusion pump, and runs through a drip chamber, which prevents air from entering the line. IVs are the preferred method of drug administration in hospital settings because they are the fastest known route of getting medication to the body. Intravenous therapy can also be used for replacing fluids, blood transfusions, and chemotherapy treatments.
Substances that are safe to infuse through an IV line include blood-based products, medications, volume expanders, and nutritional products. A blood-based product is any component of blood collected from a donor for intended use in a transfusion. While some medications are only able to be administered intravenously, many medications are best taken up by the body when administered within a vein. Volume expanders, often called crystalloids, are substances that are made up of water-soluble molecules. The most commonly used crystalloid is normal saline, which is a solution of sodium chloride at 0.9 percent concentration. Lactated Ringer’s solution is another crystalloid used with intravenous fluid administration. Buffer solutions are introduced to the body in order to correct states of acidosis or alkalosis and bring the blood pH back to an isotonic state. The most common buffer solution used in an IV is intravenous sodium bicarbonate. Parenteral nutrition is a means of feeding a person intravenously, so as to bypass eating and digestion. Recreational drugs, while said to be very unsafe, are commonly injected intravenously as well.
Intravenous therapy is most often initiated by a process known as “starting a line.” In a conventional peripheral IV, a hypodermic needle is inserted into any peripheral vein that is not inside the thoracic or abdominal cavities. With the beveled side up, the needle breaks through the layers of the skin and pierces the vein. When the needle is removed, it leaves behind a flexible, plastic catheter. The most common vein used for intravenous therapy is the medial cubital vein, primarily because it is the most easily accessed. The size of the catheter is recognized as the gauge, which identifies the diameter of the cannula. 12-14 gauges are the largest, and they are known as trauma lines because their increased size allows medical personnel to deliver large volumes of fluid in short amounts of time. 16 gauges are used primarily for blood transfusions and donations, while 22 gauges are used for pediatric lines. 18-20 gauges are the most commonly used as they are the standard size used for blood draws and infusions. The part of the IV that is left outside the skin is called the connecting hub. It joins with the infusion lines and can also be connected to a syringe.
A more invasive method of administration for intravenous therapy is through a central line. Most central lines are inserted into a large vein, such as the superior or inferior vena cava. Central lines allow IV medications to be delivered safely by eliminating the risk of the substance damaging a weaker peripheral vein. It also ensures that medications reach the heart immediately, as opposed to having to be pumped through the peripheral vascular system first. Their size allows for more than one medication to be administered at a time. However, central lines have a much higher risk of complication than a peripheral IV. They can be difficult to insert because large veins are not generally palpable, so the surrounding structures have the potential to be damaged. Bleeding, infections, and embolisms are also risks of central lines.
A peripherally inserted central catheter, also known as a PICC line, is the preferred method for prolonged intravenous therapy or when the substance being infused would cause quick damage to the peripheral line, and attempting to start a central line may be too dangerous. The risk of infection from a PICC line is much less than that of another central line because of the location of insertion. While it is safer to insert than other central lines, a PICC line is usually inserted with the help of ultrasound guidance.
Another type of central line that is common in intravenous therapy is known as a central venous line. This particular line is started in the subclavian or internal jugular veins, with some started in femoral veins. Central venous lines are favored in emergency medicine because they allow for larger amounts of medication to be administered and diluted quickly, while greatly reducing the risk of damage to the vessel walls, especially if the medication being administered has a concentration that would pose a risk to the vein.
A port is a special type of insertion device that does not have an exterior connecting piece. Instead, it is surgically inserted beneath the skin and is readily accessed with a small needle. Ports are typically used in patients needing long-term treatment therapies, such as chemotherapy, because they have a lower risk of infection and cause much less inconvenience.
Continuous intravenous therapy requires the use of an infusion pump, which regulates the amount and rate that the fluid or medication is being administered to the patient. The standard infusion set comes with a bag of fluids and a drip chamber, which allows one drop at a time to pass through. A long sterile tube is attached, and some IV infusion pumps have Y-tubes, which allows medications to be “piggy-backed.” Clamps are attached to adjust or stop the flow at any time; if the clamps of a line are completely open, the infusion is referred to as a gravity drip. Rapid infusers allow intravenous lines to work at high flow rates.
Infection is always a risk with intravenous therapy because it creates a new opening for bacteria and other foreign pathogens to enter the body, especially the bloodstream. Peripheral edema is another complication that occurs when a vein is blown and fluid is still administered, because the fluid will then travel outside the vein and into the surrounding tissues. The most serious complication associated with IVs is an embolism, which is when either a blood clot or a small mass of air travels through the line and reaches a vein. If overlooked, embolisms can be fatal.
Image Caption: Neutron(TM) Catheter Patency Device. Credit: Calleamanecer/Wikipedia (CC BY-SA 3.0)