A nasogastric (NG) tube is a medical device designed to provide a temporary, flexible pathway from the nose to the stomach. It is a long, narrow, pliable tube engineered to traverse the nasal passage and esophagus. The tube must be soft enough for insertion yet structurally sound to remain in place for days or weeks, serving as a conduit for feeding, medication delivery, or stomach decompression. Understanding the NG tube involves examining its core material, size, measurement markings, and design variations.
The Core Physical Structure of an NG Tube
The NG tube is a smooth, continuous length of tubing, often made from highly flexible polymers like polyurethane or silicone. These materials are selected for their biocompatibility and pliability, allowing the tube to navigate the body’s curves. The tubing is frequently translucent, which allows clinicians to observe the flow of contents through the central channel, known as the lumen.
The proximal end, which remains outside the body, features a specialized connector designed to link the tube to syringes, feeding pumps, or suction apparatus. These connectors are often standardized, such as the ENFit type, to help prevent accidental misconnections with other medical lines. The distal tip rests inside the stomach and has a rounded, blunt shape to minimize tissue irritation during insertion.
Just proximal to the tip are small openings, referred to as “eyes” or drainage holes, that allow fluids and contents to flow into or out of the lumen. Many NG tubes also have a radiopaque stripe running along the side. This stripe is visible on an X-ray, allowing medical staff to visually confirm the tube’s correct placement in the stomach.
Understanding Tube Sizing and Measurement Markings
The thickness, or caliber, of an NG tube is measured using the French (Fr) scale. Each French unit represents one-third of a millimeter in the tube’s external diameter, meaning a larger French number corresponds to a thicker tube. Printed along the length are distinct, dark lines or numbers, which serve as the measurement markings. These markings are spaced at regular intervals, often every 10 centimeters.
These visible centimeter markers serve as a reference point for verifying the tube’s insertion depth. Once the tube is correctly positioned, the number visible at the nostril is noted. This measurement is used to check for any tube migration or displacement, providing a quick visual confirmation of the tube’s stability.
Design Variations for Different Clinical Uses
While the single-lumen tube is the standard for administering nutrition or medication, the tube’s visual appearance changes depending on its function. A common variation is the dual-lumen tube, such as the Salem Sump, used primarily for continuous gastric suction. This tube is visually distinct because it has two separate channels running side-by-side, resulting in a slightly bulkier profile.
The dual-lumen design includes a main suction line and a second, smaller air vent channel. This air vent is often visible as a thin “pigtail” at the proximal end and is usually colored blue. The presence of this blue pigtail is the most recognizable visual feature of a tube designed for decompression.
Some fine-bore feeding tubes, which are very narrow and flexible, may include a temporary, removable guide wire or stylet. This thin, stiff wire is inside the tube to provide temporary rigidity and facilitate insertion. Once the tube is confirmed to be in the correct position, the stylet is removed, and the tube returns to its soft, pliable state.