A nasogastric (NG) tube is a flexible, hollow device temporarily inserted through the nose, down the throat and esophagus, and into the stomach. This medical tool serves a dual purpose: delivering nutritional support and liquid medications to patients who cannot safely swallow, or performing gastric decompression. Decompression involves removing air, fluid, or stomach contents to relieve pressure, often due to an intestinal blockage. Selecting the correct diameter for this tube is a precise calculation that balances patient comfort with the tube’s required function.
How NG Tubes Are Measured
The diameter of an NG tube is standardized using the French (Fr) scale, a measurement system applied to many medical instruments. The French scale measures the outer circumference of the tube, translating directly to its diameter. One French unit is equal to one-third of a millimeter (0.33 mm) in external diameter. The numerical value of the French size is directly proportional to the tube’s thickness, so a larger French number indicates a wider tube.
Sizing Based on the Tube’s Function
The primary purpose of the NG tube dictates the necessary size, as the required flow rate and viscosity of the material differ significantly between functions.
Tubes used for gastric decompression or suctioning generally require a larger bore, typically ranging from 14 to 18 French in adults. This wider diameter is necessary to effectively draw out thick stomach contents, such as blood or viscous secretions, and to reduce the likelihood of the tube becoming blocked under suction. Decompression often employs a double-lumen tube, where one channel is for suction and the other is a vent to prevent the tube from sticking to the stomach lining.
Conversely, tubes used for continuous enteral feeding or medication administration are often much smaller, usually falling between 8 and 12 French. These fine-bore tubes are preferred for comfort and are suitable for the low viscosity of standard liquid formulas and fully dissolved medications. However, highly viscous substances, such as blenderized diets or thick suspension medications, may necessitate a medium-bore tube, around 14 French, to maintain flow and prevent occlusion.
Sizing Based on Patient Age and Anatomy
Patient size and anatomical constraints are important determinants in selecting the appropriate NG tube diameter.
Adults typically tolerate a wider range of sizes, with 12 to 18 French being the standard for various applications. The adult esophagus and nasal passages can accommodate these larger diameters without undue trauma. The specific choice within this range often depends on whether the tube is intended for long-term feeding or short-term decompression.
For pediatric patients, especially neonates and infants, the size requirements are drastically smaller due to their delicate and narrow anatomy. Neonatal tubes can be as small as 3.5 to 5 French to protect the small nasal openings and the airway. Children and adolescents usually require tubes in the 8 to 12 French range. Tubes must be carefully selected to minimize irritation and the risk of pressure injury to the nasal and esophageal mucosa. Individual anatomical factors, such as a severely deviated nasal septum, require specific assessment to ensure the smallest and least traumatic tube is selected for safe insertion.
Effects of Using a Suboptimal Size
Using an NG tube that is either too large or too small for the patient or the purpose can lead to significant complications.
A tube that is oversized for the patient’s anatomy can cause trauma during insertion, resulting in bleeding, tissue erosion, and severe discomfort in the nasal passage. If left in place, an overly large tube can exert excessive pressure on the naris, leading to pressure necrosis (localized tissue death).
Selecting a tube that is too small, particularly for decompression or the administration of viscous materials, compromises the tube’s effectiveness. A narrow lumen increases the risk of tube clogging, which necessitates frequent flushing or replacement, disrupting treatment. For decompression, a small-bore tube may be unable to adequately evacuate stomach contents, leading to ineffective suctioning and persistent patient symptoms like nausea and abdominal distention.