A nasogastric (NG) tube is a flexible tube passed through the nose and down into the stomach, used to deliver nutrition, fluids, medication, or to remove stomach contents. Improper placement, such as coiling in the esophagus or entering the respiratory tract, is a life-threatening complication that can lead to aspiration pneumonia or lung perforation. Verification of the tube’s correct location in the stomach is the most important step immediately following insertion and before the tube is used. Confirmation relies on a combination of reliable methods to ensure patient safety.
Radiographic Confirmation
A chest X-ray is considered the definitive method for initial confirmation of NG tube placement, often referred to as the gold standard. This imaging technique provides a visual record of the tube’s entire path. The X-ray must confirm that the tube tip is positioned below the diaphragm and within the stomach, typically in the body or antrum.
A properly placed tube should follow the esophagus, cross the diaphragm in the midline, and have its tip clearly visible below the left hemi-diaphragm. This high level of certainty is especially relevant for patients at high risk for misplacement, such as those with impaired consciousness or a suppressed gag reflex. Radiographic confirmation is typically mandated immediately after the initial, blind insertion, prior to the first administration of any substance through the tube.
Bedside pH Testing
Bedside pH testing is a common, reliable, and more practical alternative to X-ray for initial and ongoing verification. This method involves aspirating a small amount of fluid from the tube and testing its acidity using specialized pH strips. Gastric fluid is highly acidic due to hydrochloric acid, yielding a low pH reading, which confirms the tube’s location in the stomach.
The expected pH range for fluid aspirated from the stomach is between 0 and 5.5, with guidelines suggesting a level of 5 or lower as confirmation. Conversely, aspirate from the respiratory tract tends to be more alkaline, with a pH greater than 6. Intestinal fluid is also less acidic than stomach contents, registering a pH above 7.
To perform the test, fluid is withdrawn from the tube and applied to a pH strip, which is then compared to a reference chart. A significant limitation of this method is the use of acid-suppressing medications, such as proton pump inhibitors or H2 blockers, which can artificially raise the stomach’s pH level. If a patient is taking these medications, the gastric aspirate pH may be 6 or higher, potentially confusing the results and necessitating a radiographic check for definitive confirmation.
Supplementary and Unreliable Methods
Other methods exist to support the verification process, but they should never be used as a standalone confirmation of placement. Visual inspection of the aspirated fluid can be supportive, as gastric aspirate is often clear or grassy green, while pulmonary aspirate is typically clear or straw-colored. This visual assessment is not definitive because aspirate appearance can vary widely depending on a patient’s recent intake or underlying condition.
The auscultation method, sometimes called the “air bolus” or “whoosh test,” involves injecting air into the tube while listening over the abdomen with a stethoscope for a rushing sound. This technique is now widely considered unreliable and inaccurate as a primary verification tool. The lungs and stomach are both resonant organs, meaning the sound of air entering the tube can be transmitted and heard even if the tube is misplaced in the respiratory tract. Health organizations caution against this method due to its high rate of false-positive results.
Protocol for Ongoing Verification
Verification of NG tube placement is a continuous process that must occur throughout the duration the tube is in place. The tube’s position can migrate due to coughing, vomiting, or patient movement, creating an ongoing risk of misplacement. Therefore, the tube’s location must be checked before every use, including before administering any medication, fluid flush, or feeding bolus.
The primary step in ongoing verification is the external measurement check. Tubes are marked with centimeter increments, and a change in the visible length at the nostril suggests the tube has migrated and requires re-verification. If there is any suspicion of displacement, or if the tube has been used continuously for an extended period, re-verification by bedside pH testing is necessary. If the pH test is inconclusive, or if no aspirate can be obtained, a chest X-ray must be performed again before the tube can be safely used.