A catheter is a thin, flexible, hollow tube that is inserted into the body to deliver or remove fluids, gases, or other substances — or to provide access for medical instruments. Catheters are among the most widely used medical devices in hospitals worldwide, found in every department from emergency rooms to cardiac catheterisation labs to intensive care units.
The word "catheter" comes from the Greek katheter — meaning "to send down." Their use dates back to ancient times, but modern medical catheters are precision-engineered devices made from biocompatible polymers, nitinol, and stainless steel.
"On any given day in a large hospital, dozens of different catheter types are in use simultaneously — from a simple IV cannula in the emergency room to a complex coronary guide catheter in the cath lab."
How Does a Catheter Work?
The basic principle is simple: a hollow tube creates a controlled channel between the outside world and an internal body cavity or vessel. Depending on the type:
- Fluid (urine, blood, contrast dye) drains out through the catheter
- Medication, nutrition, or saline is delivered in through the catheter
- Instruments (guide wires, balloons, biopsy forceps) are passed through the catheter's lumen
Catheters are made from materials chosen for flexibility, biocompatibility, and their specific job. Urinary catheters use silicone or latex; cardiac catheters use nylon or polyurethane; IV catheters use PTFE-coated materials.
Major Types of Catheters
1. Urinary Catheters (Foley Catheters)
The most commonly known type. A Foley catheter drains urine from the bladder when a patient cannot urinate naturally — due to surgery, anaesthesia, prostate enlargement, or neurological conditions.
- Material: Silicone or latex-free materials
- Retention mechanism: A balloon at the tip, inflated with saline after insertion to hold the catheter in place
- Sizes: 8 Fr to 24 Fr (Fr = French gauge; 1 Fr = 0.33 mm diameter)
- Duration: Short-term (days) or long-term (months, with regular changing)
- Risk: Catheter-Associated Urinary Tract Infection (CAUTI) — managed through sterile technique and minimal dwell time
2. Intravenous (IV) Catheters (Peripheral Cannulas)
The standard catheter inserted into a vein — usually on the hand or forearm — to deliver medications, IV fluids, blood products, or anaesthesia. Also called a "cannula" or "IV line."
- Common sizes: 14G (large, for rapid infusion) to 24G (small, for paediatric/elderly patients)
- Duration: Changed every 72–96 hours to prevent phlebitis (vein inflammation)
- Types: Peripheral IV, Central Venous Catheter (CVC), PICC (Peripherally Inserted Central Catheter), Hickman Line
3. Cardiac / Coronary Catheters
Used in the cardiac catheterisation laboratory (cath lab) for diagnosis and treatment of heart disease:
- Diagnostic catheters: Deliver contrast dye to visualise coronary arteries (angiogram). Examples: Judkins Left, Judkins Right, Amplatz, Multipurpose
- Guiding catheters: Larger-bore catheters that provide a channel through which guide wires, balloons, and stents are delivered during PCI (angioplasty)
- Balloon catheters: Used to inflate a balloon inside a narrowed artery (PTCA) to push the blockage aside
- Electrophysiology catheters: Thin, multi-electrode catheters used to map and ablate arrhythmias
- Haemodynamic catheters: Swan-Ganz (pulmonary artery catheter) for measuring pressures in ICU
4. Epidural and Spinal Catheters
Inserted into the epidural space of the spine to deliver anaesthetic agents or analgesics (pain relief). Commonly used in:
- Labour and delivery (epidural analgesia)
- Post-operative pain management
- Chronic pain syndromes
5. Nasogastric (NG) and Feeding Catheters
Inserted through the nose into the stomach or small intestine to:
- Deliver nutrition (tube feeding) when a patient cannot eat
- Drain stomach contents (gastric decompression) after surgery
- Deliver medications to unconscious or ventilated patients
6. Neonatal Umbilical Catheters (UAC / UVC)
Specific to NICU care — inserted through the newborn's umbilical artery (UAC) or umbilical vein (UVC) for:
- Continuous arterial blood pressure monitoring
- Blood gas sampling
- Delivery of IV fluids, medications, and total parenteral nutrition (TPN)
- Exchange transfusions in severe jaundice
7. Chest Drains and Pleural Catheters
Inserted into the pleural space around the lungs to drain air (pneumothorax), blood (haemothorax), or fluid (pleural effusion). Essential in thoracic surgery and trauma care.
Catheter Materials and What They Mean
| Material | Properties | Typical Use |
|---|---|---|
| Silicone | Very biocompatible, soft, long-term safe | Urinary catheters, long-term implants |
| Polyurethane | Stiff, good torque transmission, radiopaque | Cardiac catheters, guiding catheters |
| Nylon / Polyamide | Excellent pushability and torque | Diagnostic coronary catheters |
| PTFE (Teflon) | Very low friction, smooth surface | IV catheters, guide wire coatings |
| PVC | Inexpensive, flexible | Nasogastric tubes, drainage catheters |
Catheter Sizes: The French Scale
Catheters are measured in French (Fr) units: 1 French = 0.33 mm = 1/3 mm in external diameter. A 6 Fr catheter = 2 mm outer diameter. This scale is used universally in cardiac, vascular, and urological catheters.
- 4–6 Fr: Neonatal / paediatric / diagnostic coronary catheters
- 6–8 Fr: Adult guiding catheters for PCI
- 8–12 Fr: Large-bore access sheaths, chest drains
- 14–24 Fr: Urinary (Foley) catheters
Leading Catheter Brands Used in India
- Terumo — diagnostic and angiographic catheters; Radifocus introducer sheaths
- Merit Medical — balloon catheters, angiographic catheters
- Nipro — neonatal umbilical catheters (UAC/UVC), IV lines, NG tubes
- B. Braun — central venous catheters, epidural kits
- Becton Dickinson (BD) — IV cannulas, blood collection
- Medline, Pennine — urinary catheters
India's Backbone Pharma distributes Terumo, Merit Medical, and Nipro catheter ranges across India, Middle East, and Southeast Asia.
Catheter Care and Infection Prevention
Catheter-associated infections (CAUTIs for urinary, CLABSIs for central lines) are among the most common healthcare-associated infections. Prevention includes:
- Strict aseptic insertion technique with sterile gloves and drape
- Chlorhexidine skin preparation before insertion
- Daily review of catheter necessity — remove as soon as no longer needed
- Regular site inspection for signs of infection or phlebitis
- Antimicrobial-coated catheters for high-risk patients
- Closed drainage systems for urinary catheters
Frequently Asked Questions
Is catheter insertion painful?
Urinary catheter insertion can cause discomfort but is performed with lubricating gel and, in some cases, topical anaesthetic. Cardiac catheters are inserted under local anaesthesia — the patient is conscious but feels no pain at the insertion site.
What is the difference between a catheter and a cannula?
In general usage, a cannula refers to a short IV tube inserted into a peripheral vein. A catheter is typically longer and used for a more specific purpose. However, the terms are often used interchangeably for IV access.
How long can a catheter stay in?
It depends on the type: Peripheral IV cannulas are changed every 72–96 hours. Foley catheters for short-term use are removed within days; long-term catheters are changed monthly. PICC lines can stay for weeks to months. Cardiac catheters used during procedures are removed at the end of the procedure.