A nasogastric (NG) tube is a flexible tube inserted through the nose, down the esophagus, and into the stomach or small intestine. Healthcare providers use this device for delivering nutrition, administering medications, or decompressing the stomach by draining air and fluid. Confirming the tube’s exact location after insertion is paramount to patient safety because it passes close to the trachea and lungs. A misplaced tube can lead to severe complications, such as aspiration pneumonia, if fluids are mistakenly delivered into the respiratory tract.
Radiography: The Gold Standard Confirmation
Radiography, specifically a chest and upper abdominal X-ray, is the standard for confirming the initial placement of a nasogastric tube. This imaging technique provides definitive, visual confirmation of the tube’s entire path and the precise location of its tip. The X-ray must be obtained immediately after insertion and before any substance is administered through the tube.
Interpreting the radiograph requires tracing the tube’s course from the nares, past the esophagus, and across the diaphragm. For correct gastric placement, the tube’s tip should be clearly visible below the left hemi-diaphragm, typically positioned in the body of the stomach. Radiography is the only method that can reliably distinguish between the stomach, esophagus, or lungs, preventing potentially fatal errors.
While X-ray confirmation is highly accurate, misinterpretation can occur. Proper radiographic interpretation requires looking at the tube’s entire trajectory to ensure it does not deviate into the trachea or bronchus. Imaging remains the most secure method for initial verification, especially in patients unable to communicate discomfort or who have a suppressed gag reflex.
Chemical Confirmation Using pH Testing
After initial radiographic confirmation, chemical testing of the tube’s aspirate is the primary bedside verification method. This is used when an X-ray is impractical for every check. The method involves gently aspirating a small amount of fluid and testing its acidity using specialized pH indicator strips to confirm the tube tip is resting in the highly acidic environment of the stomach.
Stomach contents typically have a pH ranging from 1 to 5.5 due to hydrochloric acid. If the tube is correctly placed, the aspirate sample should register at or below 5.5 on the test strip. Respiratory secretions from the lungs are generally alkaline, with a pH of 6 or higher.
If the pH reading is above 5.5, it may suggest the tube is misplaced in the respiratory tract, coiled in the esophagus, or positioned in the intestine (which usually registers between 6 and 7). A high pH can also occur if the patient is receiving acid-suppressing medications or continuous tube feeds. To avoid a falsely high reading, pause continuous feeds for 15 to 30 minutes before testing.
If a pH reading above 5.5 is obtained, or if aspirate cannot be obtained, the tube’s position must be re-verified immediately, usually by obtaining a new X-ray, before any feeding or medication is delivered.
Identifying and Avoiding Unreliable Techniques
Historically, several methods used to check nasogastric tube placement are now known to be unreliable and potentially dangerous. The most commonly cited unsafe practice is the auscultatory method, sometimes called the “whoosh test” or air injection technique. This technique involves injecting a bolus of air into the tube while listening with a stethoscope over the epigastric area for a characteristic “whooshing” sound.
This method is highly discouraged because sound transmission through the chest is variable and cannot reliably distinguish between the stomach, esophagus, or lungs. A sound similar to the gastric “whoosh” can be heard when air enters the esophagus or the tracheobronchial tree, leading to a false sense of security. Studies have demonstrated that a significant percentage of tubes incorrectly identified as being in the stomach using this method were actually misplaced.
Other unreliable practices include observing for the patient’s cough reflex or submerging the end of the tube in water (the “bubble test”). The absence of coughing is misleading, especially in patients with decreased consciousness or impaired reflexes. The presence or absence of bubbles in water is also not a reliable indicator of correct placement and should not be used.
Ongoing Tube Checks and Monitoring
Confirmation of placement is a continuous process required throughout the time a patient has an NG tube. Before administering any feed, fluid, or medication, the tube’s position must be checked for migration. Tube migration is common and can be caused by coughing, vomiting, or changes in the patient’s body position.
A simple ongoing check is to inspect the external markings where the tube exits the nares. The tube should be secured with tape, and the external length noted after initial confirmation. Any significant change in this length suggests the tube has moved and requires further verification before use.
Visual assessment of the aspirated fluid (typically clear, grassy green, or tan) can provide a clue, but it must be paired with the chemical pH test. If there is any doubt about the tube’s location, or if the patient shows new signs of respiratory distress, the tube should not be used, and re-verification via pH testing or radiography is mandatory.