A nasogastric (NG) tube is a slender, flexible tube inserted through the nose, down the throat and esophagus, and into the stomach. Its primary function is to provide nutrition, fluids, and medications to individuals who are unable to swallow safely, or to remove air and fluid from the stomach for decompression. Before an NG tube is used for any purpose, confirming its correct placement is the most important safety measure to prevent serious harm. The tube must be securely positioned in the stomach, or the small intestine, and not mistakenly diverted into the lungs.
Consequences of Improper Placement
The most significant danger associated with NG tubes is the incorrect insertion into the respiratory tract, such as the trachea or a bronchus, instead of the esophagus. This misplacement occurs in a small but concerning percentage of blind insertions. If feeding or medication is administered into a misplaced tube, the substances will enter the lungs, a complication often referred to as “aspiration by proxy”.
Introducing formula or liquid directly into the lungs can cause severe aspiration pneumonia, lung abscess, or a life-threatening condition called pneumothorax. Because of these severe risks, administering anything through an improperly placed NG tube is considered a “never event” in many healthcare systems, meaning it is a preventable safety incident that should never occur.
Definitive Confirmation Using Imaging
Following the initial insertion of a nasogastric tube, a Chest X-ray (CXR) is considered the definitive method for confirming its position. The X-ray provides a complete visual of the tube’s path, confirming that the tip is correctly situated below the diaphragm, in the stomach. This imaging is mandatory before the tube is used for the first time.
However, radiographic confirmation is not practical for routine, repeated checks. It involves exposure to ionizing radiation, and it can be expensive and time-consuming, potentially delaying necessary feeding and medication. X-ray interpretation is not foolproof, and misinterpretation by staff has been identified as a cause of patient harm. Consequently, bedside methods are necessary for ongoing verification after the initial placement is confirmed by imaging.
Bedside Methods for Ongoing Verification
For routine, ongoing checks before every use, healthcare providers rely on non-radiological, bedside methods. The most reliable and widely recommended bedside technique involves aspirating fluid from the tube and testing its acidity, or pH. This method relies on the highly acidic nature of the stomach environment.
To perform this check, a syringe is used to gently draw a sample of fluid, or aspirate, from the NG tube. A drop of this aspirate is then placed onto specially designed pH indicator paper. A safe reading that confirms the tube is in the stomach is typically a pH value between 1 and 5.5.
A pH reading of 6 or higher is a red flag, as it suggests the tube may have migrated into a less acidic area, such as the respiratory tract, or possibly the small intestine. Certain medications, like acid-suppressing drugs, can raise the stomach’s pH above the normal range, complicating the results of this test. This method requires careful consideration of the patient’s medical status.
Checking the external measured length of the tube is also necessary. During initial insertion, the length of the tube extending from the nostril is marked and documented. Before each use, this external measurement should be compared to the documented initial length to ensure the tube has not moved. A significant change in the external length indicates that the tip may have migrated out of position, either upward into the esophagus or downward into the small intestine.
The auscultation technique involves injecting air into the tube and listening for a “whooshing” sound over the stomach with a stethoscope. Research shows this method is unreliable because a similar sound can be heard even if the tube is misplaced in the chest, leading to dangerous errors. This method should never be used as the sole or primary method of verification.
Interpreting Results and Necessary Next Steps
When the pH test is performed, a clear result of 5.5 or lower, combined with a stable external tube length, confirms the tube is in the correct gastric position. In this confirmed scenario, it is safe to proceed with the planned use, such as administering medications or starting a feeding. This dual check provides the necessary assurance for ongoing, routine use.
If the pH is found to be too high, typically 6 or above, or if there is any change in the external length measurement, an incorrect position must be suspected. If any uncertainty exists, all administration of fluids, feeds, or medications through the tube must immediately stop. The healthcare provider should be notified right away, as re-verification is required.
If aspiration of fluid is not possible, or if the pH result is inconclusive due to acid-suppressing medications, the tube’s position must be confirmed by a repeat X-ray before any further use. When in doubt about the tube’s location, no substance should ever be put down the tube.