Intravenous therapy: Encyclopedia II - Intravenous therapy - Intravenous access devices

Intravenous therapy - Intravenous access devices

Intravenous therapy - Needle and syringe

The simplest form of intravenous access is a syringe with an attached hollow needle. The needle is inserted through the skin into a vein, and the contents of the syringe are injected through the needle into the bloodstream. This is most easily done with an arm vein, especially one of the metacarpal veins. Usually it is necessary to use a tourniquet first to make the vein bulge; once the needle is in place, it is common to draw back slightly on the syringe to see blood return, thus verifying that the needle is really in a vein; then the tourniquet is removed before injecting.

This is the most common method of intravenous drug use for euphoriants such as heroin, or in any case where a person must self-administer intravenous medication at home. It is also a convenient way to deliver life-saving medications in an emergency. However, in a controlled health-care setting, direct injection is rarely used since it only allows delivery of a single dose of medication.

Intravenous therapy - Peripheral IV lines

This is the most common intravenous access method in both hospitals and paramedic services. A peripheral IV line consists of a short catheter (a few centimeters long) inserted through the skin into a peripheral vein. A peripheral vein is any vein that is not in the chest or abdomen. Arm and hand veins are typically used although leg and foot veins are occasionally used. Pediatricians sometimes use the scalp veins of infants. Part of the catheter remains outside the skin, with a hub that can be connected to a syringe or an intravenous infusion line, or capped with a bung between treatments. The caliber of cannulas is commonly indicated in gauge, with 14 being a very large cannula (used in resuscitation settings) and 24-26 the smallest. The most common sizes are 16-gauge (midsize line used for blood donation and transfusion), 18- and 20-gauge (all-purpose line for infusions and blood draws), and 22-gauge (all-purpose pediatric line). 12 and 14-gauge peripheral lines actually deliver equivalent volumes of fluid faster than central lines, accounting for their popularity in emergency medicine; these lines are frequently called "widebores" or "trauma lines."

Blood can be drawn from a peripheral IV if necessary, but only if it is in a relatively large vein and only if the IV is newly inserted. Blood draws are typically taken with specialized IV access sets known as phlebotomy kits, and once the draw is complete, the needle is removed and the site is not used again. If a patient needs frequent venous access, the veins may scar and narrow, making any future access extremely difficult or impossible; this situation is known as a "blown vein," and the person attempting to obtain the access must find a new access site proximal to the "blown" area.

Originally, a peripheral IV was simply a needle that was taped in place and connected to tubing rather than to a syringe; this system is still used for blood donation sets, as the IV access will only be needed for a few minutes and the donor may not move while the needle is in place. Today, hospitals use a safer system in which the catheter is a flexible plastic tube that originally contains a needle to allow it to pierce the skin; the needle is then removed and discarded, while the soft catheter stays in the vein. The external portion of the catheter, which is usually taped in place or secured with a self-adhesive dressing, consists of an inch or so of flexible tubing and a locking hub. Many sets contain a small amount of the anticoagulant heparin to keep the line from clotting off, and frequently are called "heparin locks" or "hep-locks."

A peripheral IV cannot be left in the vein indefinitely, because of the risk of insertion-site infection leading to cellulitis and bacteremia. Hospital policies usually dictate that every peripheral IV be replaced (at a different location) every three days to avoid this complication.

Intravenous therapy - Central IV lines

Central IV lines flow through a catheter with its tip within a large vein, usually the superior vena cava or inferior vena cava, or within the right atrium of the heart. This has several advantages over a peripheral IV:

• It can deliver fluids and medications that would be overly irritating to peripheral veins because of their concentration or chemical composition. These include some chemotherapy drugs and total parenteral nutrition.
• Medications reach the heart immediately, and are quickly distributed to the rest of the body.
• There is room for multiple parallel compartments (lumens) within the catheter, so that multiple medications can be delivered at once even if they would not be chemically compatible within a single tube.
• Carers can measure central venous pressure and other physiological variables through the line.

Central IV lines also carry higher risks of bleeding, bacteremia, and gas embolism (see Risks below).

There are several types of central IVs, depending on the route that the catheter takes from the outside of the body to the vein.

A PICC line is inserted into a peripheral vein, usually in the arm, and then carefully advanced upward until the catheter is in the superior vena cava or the right atrium. This is usually done by feel and estimation; an X-ray then verifies that the tip is in the right place.

A PICC may have two parallel compartments, each with its own external connector (double-lumen), or a single tube and connector (single-lumen). From the outside, a single-lumen PICC resembles a peripheral IV, except that the tubing is slightly wider.

The insertion site must be covered by a larger sterile dressing than would be required for a peripheral IV, due to the higher risk of infection if bacteria travel up the catheter. However, a PICC poses less of a systemic infection risk than other central IVs, because bacteria would have to travel up the entire length of the narrow catheter before spreading through the bloodstream.

The chief advantage of a PICC over other types of central lines is that it is easy to insert, poses a relatively low risk of bleeding, is externally unobtrusive, and can be left in place for months to years for patients who require extended treatment. The chief disadvantage is that it must travel through a relatively small peripheral vein and is therefore limited in diameter, and also somewhat vulnerable to occlusion or damage from movement or squeezing of the arm.

There are several types of catheters that take a more direct route into central veins. These are collectively called central venous lines.

In the simplest type of central venous access, a catheter is inserted into a subclavian, internal jugular, or (less commonly) a femoral vein and advanced toward the heart until it reaches the superior vena cava or right atrium. Because all of these veins are larger than peripheral veins, central lines can deliver a higher volume of fluid and can have multiple lumens.

Another type of central line, called a Hickman line or Broviac catheter, is inserted into the target vein and then "tunneled" under the skin to emerge a short distance away. This reduces the risk of infection, since bacteria from the skin surface are not able to travel directly into the vein; these catheters are also made of materials that resist infection and clotting.

A port (often referred to by brand names such as Port-a-Cath or MediPort) is a central venous line that does not have an external connector; instead, it has a small reservoir implanted under the skin. Medication is administered intermittently by placing a small needle through the skin into the reservoir. Ports cause less inconvenience and have a lower risk of infection than PICCs, and are therefore commonly used for patients on long-term intermittent treatment.

Adapted from the Wikipedia article "Intravenous access devices", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki