A catheter is a flexible tube made from specialized medical-grade materials designed for insertion into a body cavity, duct, or vessel. Catheters perform a wide range of functions, most commonly involving the introduction or withdrawal of fluids. The concept of using a hollow tube to access the body is ancient, with evidence suggesting their use as early as 3,000 B.C. to relieve urinary retention. The modern, flexible catheter began to take shape in the 18th century, demonstrating the long-standing necessity for these devices in patient care.
The Basic Mechanism of Action
The fundamental principle governing how many catheters work, particularly those used for drainage, relies on the physics of fluid dynamics. In urinary drainage systems, the mechanism is often driven by gravity, where the fluid flows downward from the bladder, through the catheter, and into a collection bag positioned lower than the patient. The material science of the catheter, often involving silicone, rubber, or plastic, is engineered to be biocompatible and flexible enough for comfortable insertion, yet rigid enough to maintain its structure.
The catheter itself is essentially a tube with one or more hollow channels, known as lumens. A single-lumen catheter is used purely for drainage or infusion. Multi-lumen designs allow for simultaneous functions, such as draining fluid through one channel while administering medication or monitoring pressure through another. For indwelling urinary catheters, a second, smaller channel is used to inflate a small balloon near the tip with sterile water once the device is inside the bladder. This retention balloon secures the catheter in place, preventing accidental dislodgement and allowing for continuous drainage.
Differentiating Types by Function
Catheters are categorized by their specific medical function and insertion location. Urinary catheters are the most common type, primarily used for bladder drainage. Indwelling catheters, like the Foley catheter, are designed to remain in the bladder for an extended period, secured by the retention balloon.
Intermittent catheters are inserted temporarily to empty the bladder and are immediately removed after use. This method is closer to natural urination and carries a lower risk of long-term infection. Vascular catheters focus on blood vessels, providing access to the circulatory system. Peripheral intravenous (PIV) catheters are short tubes inserted into small veins, typically in the arm, for short-term fluid and medication administration. Central venous catheters (CVCs) are longer and placed into large veins near the heart, often in the neck or chest, providing reliable, long-term access for chemotherapy, dialysis, or intensive monitoring. Specialized catheters exist for diagnostic or interventional procedures, such as angiographic catheters that deliver contrast dye to visualize coronary arteries.
Reasons for Catheterization
The decision to use a catheter is based on specific medical needs that require internal access for monitoring, drainage, or delivery. One of the most frequent indications is the relief of urinary retention, where a blockage or nerve damage prevents the bladder from emptying naturally, often due to conditions like prostate enlargement or post-surgical swelling. Failure to drain the bladder can lead to dangerous pressure build-up and potential kidney damage.
Catheters are also used for critical care monitoring, allowing medical staff to obtain a measurement of a patient’s fluid output, which is an indicator of kidney function and overall stability. In vascular applications, they provide a reliable conduit for administering large volumes of intravenous fluids, nutrients, or medications directly into the bloodstream. Furthermore, they are used to access specific internal structures for imaging studies, guiding diagnostic tools to an exact location within the body.
Management and Duration of Use
Catheterization can be classified as short-term or long-term, depending on the patient’s condition and expected duration of need. Short-term use is common following surgery, where the device is removed as soon as the patient regains the ability to urinate independently, usually within days. Long-term use, defined as more than 30 days, is necessary for individuals with chronic conditions like spinal cord injuries or permanent nerve damage.
Proper management is necessary to mitigate the risk associated with catheter use, which is a catheter-associated urinary tract infection (CAUTI). Hygiene practices involve regularly washing hands and the insertion site with soap and water before and after handling the device. Healthcare providers should ensure the catheter and drainage system remain sealed and unobstructed to prevent the reflux of microorganisms. Patients and caregivers are advised to monitor for signs of infection and seek medical attention if these symptoms appear:
- Fever
- Chills
- Cloudy urine
- Foul-smelling urine