An intravenous (IV) line is a medical device consisting of a small, flexible catheter inserted into a blood vessel to deliver fluids, medications, or blood products directly into the bloodstream. The term “IV” is short for “intravenous,” meaning “within the vein,” which reflects that the vast majority of these procedures are performed by placing the catheter into a vein. Healthcare providers use the venous system as the standard route for infusion therapy due to its accessibility and low risk.
The Primary Target: Understanding Veins
Veins are the chosen vessels for standard IV access because their physiological characteristics make them safe and efficient for fluid administration. The venous system carries deoxygenated blood back toward the heart, allowing the infused substance to quickly circulate throughout the body. Veins are generally positioned more superficially, making them easier to locate and access compared to arteries, which are typically situated deeper.
Veins operate under a much lower pressure system because the blood flow is not directly propelled by the forceful pumping action of the heart. This low pressure minimizes the potential for significant bleeding upon insertion of the catheter. Furthermore, the walls of veins are thinner and less muscular than those of arteries, allowing for easier and less painful penetration.
Why Arteries Are Avoided for Standard IVs
Arteries are intentionally avoided for standard IV infusions because their function and structure create considerable safety risks. Arteries carry oxygenated blood away from the heart and are subjected to the full force of the heart’s contractions. This results in very high internal pressure, evident in the strong, pulsatile flow of blood.
Puncturing an artery to place a standard IV can lead to immediate complications, including difficulty stopping the bleeding and the formation of a hematoma at the insertion site. The most severe risk is the accidental infusion of medication into the artery. Since arterial flow is away from the heart and directly into the capillary network supplying the limb, concentrated medication can cause an arterial spasm.
This spasm or chemical irritation from the drug can restrict or completely cut off blood supply to the tissues downstream. This lack of oxygen and nutrients, called ischemia, can lead to severe tissue damage, including necrosis, gangrene, and potential loss of the limb. If an arterial puncture is suspected—often indicated by bright red, pulsatile blood—the procedure must be immediately stopped and firm pressure applied.
When Arteries Are Accessed (And Why It’s Different)
While standard IVs are strictly placed in veins, specific, specialized medical procedures require intentional arterial access. These procedures involve specialized equipment and focus on monitoring or diagnostic goals, not the infusion of large volumes of fluid or medication. One such technique is the placement of an Arterial Line (A-line), typically inserted into the radial artery in the wrist.
The primary purpose of an A-line is to provide continuous, real-time monitoring of a patient’s blood pressure, which is particularly important in critical care or surgical settings. Arteries are also accessed to draw an Arterial Blood Gas (ABG) sample, a diagnostic test measuring the levels of oxygen and carbon dioxide in the blood. These procedures are performed by trained professionals and are fundamentally different from the therapeutic drug and fluid delivery of a standard IV.