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Intravenous therapy

Intravenous therapy (IV) is a therapy that delivers liquid substances directly into a vein (intra- + ven- + -ous). The intravenous route of administration can be used for injections (with a syringe at higher pressures) or infusions (typically using only the pressure supplied by gravity). Intravenous infusions are commonly referred to as drips. The intravenous route is the fastest way to deliver medications and fluid replacement throughout the body, because the circulation carries them. Intravenous therapy may be used for fluid replacement (such as correcting dehydration), to correct electrolyte imbalances, to deliver medications, and for blood transfusions.

Central IV lines carry risks of bleeding, infection, gangrene, thromboembolism and gas embolism (see Risks below). They are often more difficult to insert correctly as the veins are not usually palpable and rely on an experienced clinician knowing the appropriate landmarks and/or using an ultrasound probe to safely locate and enter the vein. Surrounding structures such as the pleura and carotid artery are also at risk of damage with the potential for pneumothorax or even cannulation of the artery.

The insertion site requires better protection than that of a peripheral IV line, due to the higher risk of serious infection if bacteria travel up the catheter. However, a PICC poses less of a systemic infection risk than other central IV lines, because the insertion site is usually cooler and drier than the sites typically used for other central lines. This helps to slow the growth of bacteria which could reach the bloodstream by traveling under the skin along the outside of the catheter.

The tubing from the bag of fluid being administered that connects to directly to the patient is called the primary tubing. Any additional IVs to be administered are connected to the primary tubing and are called secondary IV, or IV piggyback; this is done instead of placing multiple catheters in the patient. When administering a secondary IV medication, the primary bag is held lower than the secondary bag so that the secondary medication can flow into the primary tubing, rather than fluid from the primary bag flowing into the secondary tubing. The fluid from the primary bag is needed to help flush any remaining medication from the secondary IV from the tubing into the patient.

Medications may be mixed into the fluids mentioned above. Compared with other routes of administration, such as oral medications, the intravenous route is the fastest way to deliver fluids and medications throughout the body. The bioavailability of the IV medication is 100%, unlike oral medications where much of the medication is lost in digestion before entering circulation. Certain types of medications can only be given intravenously, such as when there is insufficient uptake by other routes of administration such as enterally. Examples include intravenous immunoglobulin and propofol.

Blood substitutes (also called 'artificial blood' or 'blood surrogates') are artificial substances aiming to provide an alternative to blood-based products acquired from donors. The main blood substitutes used today are volume expanders such as crystalloids and colloids mentioned above. Also, 'oxygen-carrying substitutes' are emerging.

The most convenient site is often the arm, especially the veins on the back of the hand, or the median cubital vein at the elbow, but any identifiable vein can be used. Often it is necessary to use a tourniquet which restricts the venous drainage of the limb and makes the vein bulge. Once the needle is in place, it is common to draw back slightly on the syringe to aspirate blood, thus verifying that the needle is really in a vein. The tourniquet should be removed before injecting to prevent extravasation of the medication.

Catheter shearing is a very infrequent complication, but a very real danger. Shearing occurs when part of the catheter is cut by the sharp bevelled edge of the trochar. The sheared section may completely separate from the main body of the catheter, and become free floating in the blood stream. The majority of the time, it is due to poor technique, but infrequently a poorly manufactured catheter may break from the hub or shear. Infection, and a foreign body embolus are the two threats to the patient.