Catheter

A catheter is a thin, specialized tube used in medical settings.

These devices are made from medical-grade materials. They serve many different functions in healthcare. Doctors use them to treat diseases or assist in surgical procedures. A catheter can be inserted into a body cavity, a duct, or a blood vessel. It might even be placed into the brain or through the skin. The process of inserting these tubes is known as catheterization. Depending on the task, a catheter may be soft and flexible or quite stiff.

Catheters work through several specific mechanical functions. They can be used to drain fluids from the body. For example, a urinary catheter drains urine from the bladder through the urethra. If the urethra is damaged, doctors use suprapubic catheterization through the lower abdomen. Other types, like a pigtail catheter, can drain air from around the lungs during a pneumothorax. Catheters also act as delivery systems for fluids or gases. A tracheal tube can deliver oxygen or anesthetic gases directly into the lungs. In vascular medicine, catheters allow for the administration of intravenous fluids, medications, or parenteral nutrition. They can also be used to measure blood pressure in an artery or intracranial pressure in the brain.

There are many distinct types of catheters designed for specific medical needs. Diagnostic catheters are used in angiography to help visualize blood vessels. Doctors inject a radiocontrast agent through these tubes to create images using CT scans or fluoroscopy. Specific shapes exist for different paths, such as the Cobra catheter for the abdomen or the Sidewinder for the aorta. Balloon catheters are used during angioplasty to treat narrowed vessels. These include plain balloons, drug-coated balloons, and high-pressure balloons. Some even feature small blades called endotomes to cut through tough scar tissue. There are also specialized dialysis catheters used to manage blood flow for patients needing kidney support.

The history of the catheter spans thousands of years. Ancient Egyptians crafted them from reeds. The Romans, Greeks, and Hindus used tubes made of wood or precious metals. In 1752, Benjamin Franklin invented a flexible catheter to help his brother, John, who had bladder stones. Franklin's design used metal segments connected by a wire to provide rigidity. In 1844, Claude Bernard used a catheter for cardiac catheterization on a horse. Later, in 1929, Werner Forssman performed the first central venous catheterization. This breakthrough led to a Nobel Prize in Medicine in 1959 for Forssman, André F. Cournand, and Dickinson W. Richards. In the 1940s, David S. Sheridan invented the modern disposable catheter. He was later called the "Catheter King" by Forbes magazine.

Materials science is vital to how these devices function. Most catheters are made from polymers, which are types of plastics. Silicone rubber is a common choice for implants because it is inert. This means it does not react with body fluids. However, silicone can sometimes suffer from mechanical fractures. For interventional procedures, engineers use polymer-metal composites. These might include nylon, polyurethane, or polyimides. To provide strength, these materials are often layered over stainless steel braiding or tubing.

Some catheters feature a lubricious coating. This creates a slippery film to reduce friction during insertion. Guiding catheters often use a multi-layer design. They may have a PTFE inner layer for smoothness, a stainless steel braid for support, and a nylon outer layer to maintain shape.

While highly useful, catheters carry certain medical risks. Any foreign object in the body can cause an infection. Bacteria can use a catheter as a "superhighway" to enter the bloodstream. Because catheters can be difficult to clean, they may harbor antibiotic-resistant bacteria. There is also a risk of thrombus formation, which is a blood clot. This risk increases if the catheter is left in the body for a long time. Larger catheters can also increase this risk by blocking normal blood flow. Some materials, like hydrophobic Teflon, may have a higher risk of clotting than polyurethane. To prevent clotting when not in use, doctors may fill catheters with a catheter lock solution.

Catheters connect many different fields of medical science. They link urology, cardiology, neurology, and respiratory care. They are essential tools in both clinical treatment and preclinical research. In research, special probes help scientists sample proteins, antibodies, and nanoparticles. They also allow for the study of neurotransmitters and enzymes. By providing access to the most delicate parts of the human body, catheters enable modern life-saving technologies. They allow for everything from simple fluid drainage to complex heart repairs using stents.