The Intravenous line, commonly called an IV, is a method used to deliver fluids, medications, or blood products directly into a vein. This delivery system bypasses the digestive tract, allowing for immediate entry into the bloodstream for rapid effect. When people refer to an “IV,” they are describing a complex setup, not just a single needle.
The Part That Enters the Vein
The component that remains inside the body is a soft, flexible plastic tube called a catheter or cannula. When the IV is first inserted, a sharp steel needle is used to puncture the skin and guide the catheter into the vein. The needle is immediately retracted and discarded, leaving only the pliable catheter behind inside the blood vessel.
The portion of the device resting on the skin is the catheter hub, a small plastic piece that serves as the connection point for the rest of the IV system. A transparent dressing, often a clear, breathable film, is placed over this site to secure the catheter and allow the insertion point to be continuously monitored. The hub is often color-coded, indicating the catheter’s internal diameter, known as its gauge.
A smaller gauge number indicates a larger diameter, which allows fluids to flow more quickly. For example, an 18-gauge catheter (green hub) is used for rapid fluid administration or blood transfusions. A smaller 22-gauge catheter (blue hub) is used for patients with smaller or more fragile veins.
The External Delivery System
Attached to the catheter hub is the external delivery system, which consists primarily of sterile, clear plastic tubing that extends to the fluid source. This tubing is designed to be flexible and long enough to allow a patient some degree of movement. Along the length of this tubing, healthcare staff can find small ports, often called Y-sites, which are used to inject additional medications directly into the line.
Closer to the fluid bag is the drip chamber, a clear, semi-rigid plastic cylinder that hangs vertically and is filled partially with the IV fluid. The fluid passes from the bag through a sharp spike and into this chamber, where it forms visible drops that allow nurses to estimate the flow rate when a pump is not being used. The drip chamber also serves a protective function by trapping any small air bubbles that may enter the line, preventing them from reaching the patient’s bloodstream.
The fluid itself is contained in a plastic bag or bottle that is suspended above the patient, typically on a metal IV pole. These bags come in various sizes, ranging from small 50-milliliter volumes for intermittent medication doses, to larger 1,000-milliliter bags used for continuous hydration or drug delivery. The bag is usually clear, allowing medical staff to monitor the remaining volume and see the type of solution, such as saline or dextrose.
Controlling the Flow Rate
Managing the speed at which the fluid enters the vein is a necessary part of IV therapy, accomplished through one of two main methods. The simplest is a manual flow regulator, a small plastic device built into the IV tubing, often appearing as a roller clamp or dial. This mechanism physically constricts the tubing to slow or stop the flow of fluid, relying on gravity and manual adjustment to set the drip rate.
In most hospital settings, however, fluid delivery is managed by an electronic infusion pump, a boxy device usually mounted on the IV pole. These pumps are programmed to deliver a precise volume of fluid over a specific time, measured in milliliters per hour, which ensures a highly accurate and consistent flow rate. The IV tubing is threaded through the pump’s mechanism, which uses mechanical force to push the fluid along.
These electronic pumps feature digital screens where the infusion parameters are displayed. They are equipped with safety features, including alarms that sound if there is an obstruction, a change in pressure, or if the fluid bag is empty. The use of these smart pumps significantly reduces the risk of human error.
Where IVs Are Typically Placed
The choice of where to insert a peripheral IV line is dependent on the patient’s vein health, the type of fluid being administered, and patient comfort. In adults, the most common locations are the veins found on the back of the hand or in the forearm. These sites offer accessible veins that are generally able to tolerate the catheter for several days.
The veins in the inner elbow area, known as the antecubital fossa, are also frequently used, particularly for blood draws or when a larger catheter is needed. However, IVs placed near the elbow are prone to kinking or occlusion when the arm is bent, which can interrupt the flow of the infusion. For this reason, if the patient requires an IV for an extended period, a site that allows for greater joint mobility, like the back of the hand, is often preferred.