<P> Many systems of administration employ a drip chamber, which prevents air from entering the blood stream (air embolism), and allows an estimation of flow rate . </P> <P> A peripheral cannula is the most common intravenous access method utilized in both hospitals and pre-hospital services . A peripheral IV line (PVC or PIV) consists of a short catheter (a few centimeters long) inserted through the skin into a peripheral vein (any vein not situated in the chest or abdomen). This is usually in the form of a cannula - over-needle device, in which a flexible plastic cannula comes mounted over a metal trocar . Once the tip of the needle and cannula are introduced into the vein via venipuncture, the cannula is advanced inside the vein over the trocar to the appropriate position and secured, the trocar is then withdrawn and discarded . Blood samples may be drawn directly after the initial IV cannula insertion . </P> <P> Any accessible vein can be used although arm and hand veins are used most commonly, with leg and foot veins used to a much lesser extent . In infants the scalp veins are sometimes used . </P> <P> The caliber of cannula 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 are capable of delivering large volumes of fluid very fast, accounting for their popularity in emergency medicine . These lines are frequently called "large bores" or "trauma lines". </P>

Explain why iv infusion of medication is the most dangerous method to administer medication