Understanding the Nasogastric Tube
A nasogastric tube is a medical device designed for a variety of diagnostic and therapeutic procedures, such as delivering nutrition or medication, or removing fluids from the stomach. While all NG tubes share a core function, their specific components can vary greatly depending on their intended use. This guide will provide a detailed breakdown of the parts that make up the most common types of NG tubes.
The Anatomy of a Standard NG Tube
At its most basic, an NG tube is a flexible length of plastic tubing with several key features that facilitate its use and management.
Main Tube Body
- Material: The tube is typically made from clear, thermosensitive PVC or a similar biocompatible polymer. This material is flexible enough to be inserted easily but becomes more pliable and comfortable for the patient at body temperature. The transparency also allows clinicians to visualize the fluid passing through it.
- Size: NG tubes come in various diameters, measured in French (Fr) units. The size is selected based on the patient's age and the tube's purpose, with larger bores used for decompression and smaller bores for feeding.
Distal Tip and Eyelets
- Rounded Tip: The end of the tube that enters the body has a smooth, rounded tip designed to minimize trauma during insertion.
- Drainage Eyelets: Located near the distal end are several side holes, or eyelets. For decompression, these holes allow for the efficient suctioning of gastric contents, while for feeding, they ensure uniform delivery of formula.
Markings and Radio-Opaque Line
- Measurement Markings: The tube has external markings at set intervals (e.g., in centimeters or inches). These markings are crucial for estimating the insertion depth and checking for tube migration after placement.
- Radio-Opaque Line: A radiopaque strip runs the length of the tube, allowing its position to be confirmed via X-ray imaging. This is the most reliable method for verifying that the tube has been correctly placed in the stomach and not inadvertently in the respiratory tract.
Proximal Connector
- Connection Port: At the other end of the tube, a connector or port is used to attach to equipment like suction tubing, a feeding pump, or a syringe. Modern NG tubes often feature ENFit connectors, a standardized system designed to prevent misconnections with other types of medical tubing.
Specialized NG Tubes: Single vs. Double-Lumen
Double-Lumen Tube (e.g., Salem Sump™)
- Main Suction Lumen: The larger of the two channels is used for evacuating air and fluid from the stomach.
- Air Vent Lumen (Pigtail): This smaller, typically blue-capped port is a key feature. It allows atmospheric air to enter the stomach, which prevents the tube's suction eyelets from adhering to the stomach lining. This design is essential for safe, continuous gastric suctioning.
- Anti-Reflux Valve: A one-way valve may be attached to the air vent to prevent gastric secretions from leaking out.
Single-Lumen Tube (e.g., Levin or Dobhoff™)
- Single Channel: Unlike the Salem Sump, these tubes have only one channel for all functions, including feeding and medication administration. They are smaller in diameter and designed for longer-term placement.
- Weighted Tip (Dobhoff): A Dobhoff tube features a weighted end, typically containing lead or tungsten. This weight, combined with the body's natural peristalsis, helps guide the tube to a post-pyloric location in the small intestine, which may reduce the risk of aspiration.
Comparison of NG Tube Types
| Feature | Double-Lumen (e.g., Salem Sump™) | Single-Lumen (e.g., Levin, Dobhoff™) |
|---|---|---|
| Primary Use | Gastric decompression (suction) | Enteral feeding, medication delivery |
| Lumens | Two (main and air vent) | One |
| Continuous Suction | Yes, safer due to air vent | Generally not, intermittent suction used |
| Tube Size | Larger bore | Smaller bore for patient comfort |
| Tip | Rounded tip with side eyelets | Levin: Rounded tip with side eyelets Dobhoff: Weighted tip to aid placement |
| Vent Port | Yes (often blue with anti-reflux valve) | No |
| Insertion Length | Typically shorter duration | May be used for longer periods |
Practical Considerations for NG Tube Parts
Beyond understanding the basic anatomy, knowing how to manage each part of an NG tube is critical for patient safety and comfort.
- Proper Connection: Always ensure the proximal connector is properly attached to the correct equipment. Using modern ENFit connectors is a standard safety practice to prevent medication or feeding lines from being accidentally connected to IV lines.
- Maintaining the Air Vent: For a Salem Sump tube, the blue pigtail should never be clamped or used for irrigation. Its patency must be maintained by regularly flushing it with air to ensure the sump function works correctly and protects the stomach lining from injury.
- Verification of Placement: Regardless of the NG tube type, placement must be verified after insertion, typically with an X-ray, using the radiopaque line to confirm the tube's position. The measurement markings should also be checked regularly to monitor for tube migration.
Conclusion
In summary, the parts of an NG tube include the main body with measurement markings and a radiopaque line, a rounded distal tip with side eyelets, and a proximal connector for attachments. The specific function of these parts is dictated by the tube's design, with double-lumen models like the Salem Sump including a crucial air vent for safe decompression, while smaller, single-lumen tubes like the Levin and Dobhoff are optimized for feeding. With this comprehensive understanding, clinicians can better manage patient care and prevent complications. The resources at the National Institutes of Health provide further information on specific tube types and management practices, and can be referenced at the NCBI Bookshelf here: https://www.ncbi.nlm.nih.gov/books/NBK556063/.
