A nasogastric (NG) tube is a flexible, small-bore tube temporarily inserted through the nose, down the esophagus, and into the stomach. This device provides a route for delivering liquid nutrition, fluids, and medications when a person cannot swallow safely. Verifying the exact location of the tube tip within the stomach before any substance is administered is a safety requirement. This confirmation prevents severe complications that occur if the tube is mistakenly placed elsewhere.
The Critical Risks of Improper Placement
The greatest danger associated with NG tube use is misplacement into the respiratory tract, such as the trachea or a bronchus. This error can occur during initial insertion or if the tube becomes dislodged later due to coughing or vomiting. If the tube tip is positioned in the lungs and used for feeding, the substance is delivered directly into the pulmonary system.
This delivery of foreign material causes a severe and often fatal condition known as aspiration pneumonitis or pneumonia. The presence of feed in the lungs triggers an inflammatory reaction, blocking airways and impairing oxygen exchange.
Misplacement incidents are considered preventable and can lead to pneumothorax, lung damage, and death.
Gold Standard Verification Methods
Only two methods provide the definitive evidence necessary to confirm the safe placement of an NG tube. These techniques ensure the tube tip has bypassed the airway and is resting securely within the stomach. Caregivers must rely on these methods before initiating any feeding or medication administration.
Radiographic Confirmation (X-ray)
A chest and abdominal X-ray is the gold standard for confirming correct tube position immediately following a new insertion. The tube must contain a radiopaque line to be visible on the imaging. Interpretation must confirm the tube’s entire path, ensuring it follows the esophagus, avoids the bronchial tree, and its tip is clearly visible below the diaphragm.
The tip must rest below the gastroesophageal junction, ideally in the stomach. Although highly accurate, radiographic confirmation exposes the patient to radiation and can delay feeding while waiting for interpretation. Therefore, it is typically performed only upon initial placement or when other verification methods are inconclusive.
pH Testing of Aspirate
After initial X-ray confirmation, testing the acidity of fluid aspirated from the tube is the most common method for ongoing safety checks. This technique uses specially calibrated, single-use pH indicator paper to measure the acidity of a fluid sample drawn from the NG tube. Gastric fluid is highly acidic, typically yielding a pH between 1 and 5.5.
Fluid from the respiratory tract or lungs has a much higher, more neutral pH, usually 6.0 or greater. The result must be clearly \(\leq 5.5\) to confirm the tube is in a gastric location before proceeding. If the patient is taking acid-suppressing medications, the gastric pH may be elevated, making the result inconclusive and requiring further confirmation, often via X-ray.
Secondary and Insufficient Bedside Checks
Certain older practices for checking NG tube position are now considered unreliable and unsafe when used as the sole method of confirmation. These techniques lack the specificity required to definitively rule out placement in the respiratory tract. Relying on them alone has caused serious patient harm.
Auscultation (Air Injection)
The “whoosh test” involves injecting air into the tube while listening over the upper abdomen for a characteristic sound. This method is officially discouraged by major safety bodies and is not a valid way to confirm placement. The sound can be easily misinterpreted, as a similar gurgling sound can be heard if the tube is misplaced in the esophagus or the lung.
The lack of reliability makes this test a dangerous practice that provides a false sense of security. The auscultation method should never be used to verify safety before administering feed or medication.
Visual Inspection and Measurement
Visually assessing the appearance of the aspirate provides supporting information but is not a definitive test. While stomach aspirate may appear green, yellow, or clear, the color can be misleading, especially if the patient is on continuous feeds. Checking the external measurement of the tube at the nostril is a supporting step to detect migration, but it cannot confirm the tip’s exact internal location.
The tube’s length should always be marked and compared to documentation to ensure it has not shifted since the last confirmed check. However, a tube that appears to be at the correct external length could still be coiled in the esophagus or displaced into the lung, making this measurement insufficient for proving safety alone.
The Standard Verification Protocol
The fundamental rule for NG tube safety is that placement must be verified immediately before every use, including the administration of any feed, fluid flush, or medication. Even a brief delay or minor patient movement can cause the tube to shift position, necessitating a fresh safety check. This constant verification prevents a catastrophic misplacement incident.
The standard protocol involves first checking the external tube length marking to ensure no obvious displacement has occurred. This is followed by aspirating a small fluid sample and testing its pH using the appropriate indicator paper. If the pH is \(\leq 5.5\), the tube is considered safe for use, and the result must be recorded.
If the pH reading is above 5.5, the tube placement is uncertain, and administration must be stopped immediately. If this occurs, or if no aspirate can be obtained, the next step is to seek definitive confirmation via X-ray before any substance is allowed to pass through the tube. Never administer anything if the placement is unconfirmed or questionable.