A catheter is a flexible, thin tube made from medical-grade materials designed to be inserted into a body duct, vessel, or cavity. These devices are fundamental tools in modern medicine, serving a variety of purposes from diagnostics to therapeutics. Their primary function is to allow access, administer fluids or gases, or facilitate the drainage of unwanted fluids from the body. The underlying principle involves creating a temporary or long-term conduit for biological processes.
How the Device Achieves Drainage or Access
The mechanism of a catheter relies on its structure, materials, and the physics of fluid movement. Most catheters function by creating a direct channel that utilizes passive drainage, where fluid flows out due to gravity. For efficient drainage, the collection receptacle must be maintained below the level of the body cavity, such as the bladder, to ensure a continuous downward pressure gradient.
The tubing is constructed from biocompatible materials, commonly silicone, latex, or polyvinyl chloride (PVC). These materials are chosen for their flexibility and ability to reduce friction upon insertion. Many catheters are coated with hydrophilic polymers, which become slick when wet, easing passage through narrow anatomical structures like the urethra. Catheter size is standardized using the French scale, which measures the external circumference of the device.
Catheters intended to remain in place employ a dedicated retention mechanism to prevent accidental displacement. In devices like the Foley catheter, this mechanism is a small, inflatable balloon located at the tip. Once positioned within the target cavity, such as the bladder, sterile water is injected through a separate channel, or lumen, to inflate the balloon. The inflated balloon anchors the catheter securely against the internal wall of the organ, allowing for continuous drainage.
The internal architecture of a catheter varies depending on its intended use. A simple intermittent catheter has only a single lumen for fluid drainage, as it is inserted and removed immediately after use. Indwelling catheters often feature a two-way design: one large channel for drainage and a second, smaller channel dedicated to inflating the retention balloon. Specialized three-way catheters include a third lumen to allow for continuous irrigation of the cavity, such as flushing the bladder to clear debris.
Different Types Based on Medical Use
Catheters are broadly categorized by the body system they access. Urinary catheters are the most recognized type, including Indwelling (Foley) catheters which provide continuous, long-term drainage. Intermittent catheters are straight tubes used for temporary drainage, inserted multiple times daily by the user and then immediately removed. A suprapubic catheter is an indwelling variation, inserted directly into the bladder through a small incision in the lower abdomen, often used when the urethral route is compromised.
Vascular catheters are designed for insertion into blood vessels to manage the circulatory system. A peripheral intravenous (IV) catheter is a short, flexible tube placed in a vein, usually in the arm, to administer medication or fluids. Central Venous Catheters (CVCs) are longer, placed in a large vein (e.g., jugular or subclavian) with the tip resting near the heart, used for long-term medication, nutrition delivery, or monitoring central pressures.
Specialized catheters are tailored for specific diagnostic and therapeutic procedures. A cardiac catheter is guided through a blood vessel into the heart to measure blood pressure, collect blood samples, or inject dye for imaging the coronary arteries. Drainage catheters, such as nephrostomy tubes, are placed percutaneously (through the skin) into the kidney. This diverts urine flow when the ureters are blocked, preventing damaging back pressure.
Proper Insertion and Daily Management
Catheter insertion is performed by trained medical professionals following strict protocols to maintain a sterile field and minimize infection risk. The process begins with meticulous hand hygiene and the use of sterile gloves and drapes to prevent the introduction of bacteria. A local anesthetic gel is often applied to the insertion site to lubricate the catheter and reduce patient discomfort as the tube is advanced.
The catheter is gently threaded along the natural pathway until the tip is positioned, confirmed by the return of fluid (e.g., urine). Once positioned, the retention balloon is inflated, and the external tubing is secured to the patient’s skin with a fixation device. This anchoring prevents movement or traction on the catheter, which could cause internal irritation or injury.
Daily management focuses on rigorous hygiene and maintaining an unobstructed flow path. The insertion site and surrounding skin must be cleaned at least once daily with mild soap and water to prevent bacterial buildup. The drainage bag must be kept below the level of the bladder to ensure continuous, one-way flow and prevent backflow. The collection bag should be emptied when it is approximately two-thirds full to avoid excessive weight and strain on the tubing.