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Intravenous Infusion

Intravenous (aka parenteral) therapy is the administering of liquid substances directly into the circulatory system, via a vein. It can be intermittent or continuous. Continuous administration is called an intravenous drip.

The word intravenous simply means "within a vein", but is most commonly used to refer to IV therapy. Compared with other methods of administration, the intravenous route is the fastest way to deliver fluids and medications throughout the body. Some medications, as well as blood transfusions can only be given intravenously.

This therapy may be required when a casualty loses a large quantity of body fluids as a result of injury and/or shock. To halt and reverse shock, lost fluids must be replaced. If a casualty cannot take (enough) fluids by mouth, fluids must be administered by other means. When whole blood is administered, the technique is called transfusion. When sterile fluids (blood, volume expanders) are administered, the technique is called infusion.

Generally intravenus infusion is used for three major reasons:
  • To add fluid volume to the circulatory system when there is an imbalance or depletion of normal body fluids, (i.e. burns, haemorrhage)
  • To establish and maintain life support for a casualty whose condition is questionable and it is felt that the person might deteriorate
  • To provide an access for the administration of medications
IV Fluids Bag
The use of Peripheral IV lines is the most common intravenous access method. A peripheral IV line consists of a short catheter inserted through the skin into a peripheral vein (a vein which is not in the chest or abdomen). Arm and hand veins are typically used, although leg and foot veins can also be used. On infants the scalp veins are sometimes used.

An intravenous catheter is a flexible plastic tube that originally contains a needle to allow it to pierce the skin. The needle is then removed 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.

For centrally placed IV lines, sets and flushes contain a small amount of the anticoagulant heparin to keep the line from clotting off, and frequently are called "heparin locks" or "hep-locks". However, heparin is no longer recommended as a locking solution for peripheral IVs; saline is now the solution of choice for a "vac lock".

The part of the catheter which remains outside the skin is often referred to as connecting hub. This can be connected to a syringe or an intravenous infusion line, or capped with a bung between treatments. Ported cannulaes have an injection port on the top that can be separately used to administer medications.

A peripheral IV cannot be left in the vein indefinitely, because of the risk of insertion-site infection leading to phlebitis, cellulitis and sepsis. Depending on local guidelines the cannula may need to be replaced approximately every 96 hours.
Drip chamber
The calibre (tubular diameter) of a cannula is commonly indicated in gauge, ranging from 14 (a very large cannula often used in resuscitation settings) to 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 "large bores" or "trauma lines".

If required, blood can be drawn from a peripheral IV, 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 future access extremely difficult or impossible.

This is sometimes referred to as a blown vein and a new access site proximal to the "blown" area must be found for future treatment.
Intravenous catheters
           

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