A nasogastric (NG) tube is a flexible, hollow device temporarily inserted through the nose, down the esophagus, and into the stomach. Selecting the correct size directly impacts patient comfort, safety, and the intervention’s effectiveness, whether for feeding or gastric decompression. Choosing a tube that is too large increases the risk of nasal trauma and discomfort. Conversely, a tube that is too small may not function correctly, leading to clogging or inefficient drainage. This information provides general educational guidelines and is not a substitute for professional medical judgment.
The French Scale of Measurement
The standard unit used to measure the outer diameter of an NG tube is the French (Fr) scale, also known as the French gauge or Charrière scale. This system is applied to many types of medical catheters and tubes. The French unit is a direct measurement of the tube’s external diameter.
One French unit is equivalent to one-third of a millimeter (0.33 mm) in outer diameter. To determine the diameter in millimeters, the French size is divided by three. A direct relationship exists where a higher French number indicates a larger outer diameter of the tube. For example, a 15 Fr tube is five millimeters in diameter, making it wider than a 9 Fr tube, which is three millimeters in diameter.
Sizing Based on Patient Population
The initial selection of an NG tube size is determined by the patient’s age and anatomical size. In adult patients, the general size range is between 10 Fr and 18 Fr. Tubes in the 16 Fr to 18 Fr range are considered larger-bore and are selected for robust adults or when a wide lumen is required. A patient’s body habitus, which includes their size and build, is a factor in determining the largest comfortable size that can be safely passed through the nasal passage and esophagus.
Sizing is varied in pediatric populations, including neonates, infants, and children. For the smallest patients, such as neonates, sizes often range from 5 Fr to 8 Fr to minimize trauma to delicate tissues. Infants typically require tubes between 8 Fr and 10 Fr for feeding and medication delivery.
As a child grows, the tube size increases incrementally, with older children and adolescents typically using sizes from 10 Fr to 14 Fr. A rough estimate for pediatric sizing can be calculated by adding 16 to the child’s age in years and then dividing that sum by two to find a suitable French size. Regardless of the formula used, the final size must be appropriate for the child’s body size and the diameter of their naris and pharynx.
Adjusting Size for Tube Function
Once the appropriate anatomical size range is established, the tube’s intended function refines the final size selection. For enteral nutrition (feeding), smaller bore tubes are preferred, typically ranging from 8 Fr to 12 Fr. These narrower tubes are associated with greater patient comfort and a reduced risk of complications like nasal irritation, especially for continuous or long-term feeding.
In contrast, when the goal is gastric decompression, such as removing air or draining thick gastric contents, a larger bore tube is necessary. Tubes in the 14 Fr to 18 Fr range are used for this purpose, as a wider lumen is required for efficient suction and drainage. The increased diameter helps prevent clogging by viscous fluids, blood clots, or solid particles.
The viscosity of the material passing through the tube is a major functional consideration. For patients receiving high-density formulas, certain medications, or formulas with added fiber, a tube on the larger end of the feeding spectrum (12 Fr or 14 Fr) may be selected. This selection maintains flow and reduces the risk of tube occlusion. A larger diameter handles the thicker consistency, balancing effective delivery with patient comfort.