An angiocatheter is a common medical device used to establish short-term access to a patient’s bloodstream. It is frequently referred to as a peripheral intravenous (IV) catheter, and it is a simple tube-and-needle system designed for venipuncture. Once placed, the catheter allows healthcare providers to administer intravenous fluids, medications, or blood products.
Anatomy and Primary Function
The angiocatheter assembly is composed of two main functional parts that work together during insertion. The first is the sharp, hollow inner needle, often called the stylet, which pierces the patient’s skin and the wall of the vein. The stylet acts as a temporary guide that facilitates the placement of the access line.
Surrounding the stylet is the flexible, thin plastic outer tube, known as the cannula, which is the part that remains inside the vein after the procedure. The cannula is made of a polymer material designed to be well-tolerated by the body. At the back of the catheter assembly is a clear section called the flashback chamber. When the tip of the inner needle successfully enters the vein, a small amount of blood flows back into this chamber, visually signaling successful venous access.
The primary function of this entire mechanism is to establish temporary peripheral venous access for therapeutic purposes. This access point allows continuous or intermittent infusion therapy without the need for repeated needle sticks. Once the cannula is secured within the blood vessel, the system enables immediate administration of solutions like saline or dextrose, ensuring a direct route to the circulatory system.
The Step-by-Step Insertion Procedure
Placing an angiocatheter begins with selecting a suitable vein, often in the hand or arm, and applying a tourniquet to engorge the vessel. The insertion site is then cleaned using an antiseptic solution to minimize the risk of introducing bacteria into the bloodstream. Vein stabilization is performed by pulling the skin taut below the chosen site to prevent the vein from rolling during insertion.
The angiocatheter, with the stylet inside the cannula, is inserted through the skin at a shallow angle, typically between 10 and 30 degrees. The assembly is advanced until the flashback of blood appears in the chamber, confirming the needle tip has entered the vein. Once flashback is observed, the entire unit is advanced slightly further to ensure the flexible cannula tip is also inside the vein.
The angle of the assembly is lowered to be nearly parallel with the skin surface. The flexible cannula is then threaded into the vein while the stylet is held stationary. After the cannula is fully advanced to the hub, the tourniquet is released, and the inner needle is withdrawn and immediately disposed of in a sharps container. The remaining cannula is attached to an extension set, flushed with saline to confirm patency, and secured with a sterile dressing.
Common Gauges and Specific Applications
Angiocatheters are classified by a standardized gauge system that describes the inner diameter of the cannula. This system uses an inverse relationship: a lower gauge number corresponds to a larger catheter diameter and a greater potential fluid flow rate. The appropriate gauge selection is based on the patient’s clinical condition and the required infusion therapy.
Small catheters, such as 22-gauge (blue) or 24-gauge (yellow), are used for routine intravenous medications, hydration, or in patients with smaller or fragile veins, like pediatric or elderly individuals. These smaller sizes are easier to insert and cause less trauma to the vessel wall.
Larger gauges, such as 18-gauge (green) or 16-gauge (gray), are reserved for situations demanding rapid fluid or blood product administration. The largest sizes, like the 14-gauge (orange) catheter, are used in emergency and trauma settings where massive blood loss requires immediate, high-volume fluid resuscitation. Using a large-bore catheter for rapid infusion prevents resistance from slowing down the flow rate, which directly impacts the speed at which therapies can be delivered.