A cannula is a thin, flexible tube inserted into the body to deliver or remove fluids, gases, or medications. It’s one of the most common medical devices you’ll encounter in a hospital, urgent care clinic, or even at home. The two types people run into most often are the IV cannula, placed into a vein to deliver fluids or medication, and the nasal cannula, a lightweight tube that loops over the ears and rests just inside the nostrils to supply supplemental oxygen.
IV Cannulas and How They Work
An intravenous (IV) cannula is a short, flexible tube, usually made of a soft plastic like Teflon, that sits inside a vein so fluids, medications, or blood products can flow directly into your bloodstream. You’ll hear it called a “peripheral line” or simply an “IV.” It has two key parts: the thin tube itself and a small plastic hub that stays on the surface of your skin, where nurses connect syringes or fluid bags.
To place one, a healthcare provider ties a tourniquet a few inches above the insertion site to make the vein easier to see and feel. After cleaning the skin with antiseptic, they hold the device by its hub, stretch the skin taut, and insert a needle at a shallow angle. Once a small flash of blood appears in a clear chamber (confirming the needle is in the vein), the flexible tube is slid forward over the needle and the needle is pulled out and discarded. The hub is then taped down, and a quick saline flush confirms everything is flowing properly with no swelling at the site.
The whole process takes under a minute in experienced hands. If you’ve ever been told “just a small pinch,” this is what they were doing. Some facilities apply a numbing cream beforehand, especially for children or patients with needle anxiety.
How Long an IV Cannula Stays In
CDC guidelines recommend that peripheral IV cannulas in adults don’t need to be replaced more often than every 72 to 96 hours to keep infection and inflammation risk low. In children, replacement is based on clinical signs rather than a set schedule. If the duration of IV therapy is expected to go beyond six days, a longer-term catheter is typically used instead of a short peripheral line.
A cannula should be removed immediately if you notice warmth, tenderness, redness, or a firm cord-like feeling along the vein. These are signs of phlebitis, which is inflammation of the vein wall. In hospitalized adults, infiltration (where fluid leaks into surrounding tissue instead of staying in the vein) is the most common complication, occurring in roughly 18% of cases, followed by blockage at about 11% and phlebitis at about 10.5%. The vast majority of these complications are mild, grade 1 events. Placement on the back of the hand carries a higher blockage risk, while the inner elbow area is linked to a higher chance of infiltration.
Nasal Cannulas for Oxygen Therapy
A nasal cannula is a lightweight tube with two short prongs that sit just inside your nostrils. It connects to an oxygen source and delivers a steady, low flow of supplemental oxygen while you breathe normally. Standard nasal cannulas run at flow rates between 1 and 6 liters per minute, and for every additional liter of flow, the oxygen concentration you breathe in rises by about 4%. That gives a range of roughly 24% to 44% oxygen, compared to the 21% in normal room air.
This type of cannula is comfortable enough for extended wear, which is why it’s the go-to device for people on home oxygen therapy, patients recovering from surgery, and anyone who needs a modest oxygen boost without a full face mask. You can eat, drink, and talk while wearing one.
High-Flow Nasal Cannulas
For more serious breathing problems, a specialized version called a high-flow nasal cannula can deliver heated, humidified oxygen at rates up to 60 liters per minute, with oxygen concentrations adjustable anywhere from 21% to 100%. The system includes a flow generator, an oxygen blender, and a humidifier that warms the gas to body temperature (31 to 37°C) so it doesn’t dry out the airways.
High-flow therapy generates a small amount of positive pressure in the airways, roughly 1 centimeter of water pressure for every 10 liters of flow with the mouth closed. That gentle pressure helps keep the lungs open and reduces how hard the breathing muscles need to work. It’s used in acute respiratory failure, recovery after surgery, severe COPD flare-ups, and heart failure with fluid in the lungs. In patients with advanced COPD, flow rates above 30 liters per minute have been shown to lower the breathing rate and reduce diaphragm effort.
Cannulas in Surgery
Beyond IVs and oxygen delivery, cannulas play a role in several surgical procedures. In liposuction, a specialized cannula is inserted through small incisions to suction out fat tissue. These surgical cannulas come in a range of diameters, typically between 2 and 4 millimeters, and the tip usually has multiple small holes with a blunt design to minimize tissue damage.
The size a surgeon chooses depends on the goal. A 2.5 mm cannula tends to preserve fat cell quality better, making it the preferred choice when the harvested fat will be reinjected elsewhere, such as in breast reconstruction. For more delicate work like facial rejuvenation, a thinner 2 mm cannula is used to produce finer fat particles and reduce the risk of small cysts forming under the skin. Larger diameters, 3 to 4 mm, are used when the priority is removing larger volumes of fat efficiently.
Cannulas also appear in other surgical contexts: draining fluid collections, accessing the abdominal cavity during laparoscopic surgery, and delivering anesthesia during eye procedures. The basic principle is always the same, a thin tube providing controlled access to a specific area of the body, but the material, diameter, and tip design vary widely depending on the job.