A nasogastric (NG) tube is a flexible tube inserted through the nose, down the esophagus, and into the stomach. Its primary applications involve administering medications and nutrition (enteral feeding) or decompressing the stomach to remove accumulated fluid and air. Ensuring the tube is correctly positioned in the stomach and not accidentally placed in the lung is critical. Misplacement into the respiratory tract can lead to life-threatening complications, such as aspiration pneumonia and pneumothorax, if feeding or medications are introduced. Therefore, rigorous verification of the tube’s location is essential in NG tube management.
Quick Assessment Using Aspirate and pH Testing
Verification of NG tube placement is routinely performed at the bedside using aspirate analysis and pH testing. This method relies on the highly acidic nature of the stomach environment to confirm the tube’s tip location. The process begins by gently withdrawing a small sample of fluid (aspirate) from the tube using a syringe.
The visual characteristics of the aspirate provide an initial indication of placement. Gastric fluid is often grassy green, clear, or colorless, sometimes containing mucus. Respiratory secretions are typically clear and thin, while intestinal aspirate may appear bile-stained. However, visual inspection alone is not considered reliable enough for confirmation.
The definitive bedside check involves testing the aspirate’s acidity using specialized pH indicator strips. A correct gastric placement is indicated by a pH reading of 5.5 or lower, reflecting the stomach’s natural acidity. If the tube has entered the lungs, the respiratory aspirate will typically have a higher, more alkaline pH, often 6 or greater.
A pH value above 5.5 does not automatically mean the tube is misplaced in the lung. This reading could indicate the tube is in the small intestine or that the patient is taking acid-suppressing medications. Continuous enteral feeding can also buffer the stomach acid, artificially raising the gastric pH. When a high pH reading is obtained, further assessment, including a pause in feeding and retesting or obtaining a definitive X-ray, is required before the tube can be safely used.
Definitive Verification Through Imaging
Chest and abdominal radiography (X-ray) remains the definitive method for confirming the initial placement of a newly inserted NG tube. This imaging technique is considered the standard because it provides a clear, visual representation of the tube’s entire path. Radiographic confirmation is mandatory before the tube is used for the first time, especially for feeding.
To confirm correct positioning, clinicians look for the tube’s tip to be visibly positioned below the diaphragm and in the distal stomach. The tube’s path must follow the esophagus, avoiding the bronchi, and the tip must be clearly located below the left hemi-diaphragm. This ensures the tube is not curled in the esophagus or accidentally inserted into the respiratory tree.
While X-ray is the most reliable method, misinterpretation of the image has been a reported cause of harm. Routine X-rays for subsequent checks are generally avoided to limit radiation exposure, making bedside pH testing the preferred method for ongoing verification. X-ray is reserved for initial placement or any time there is uncertainty about the tube’s location.
Why Some Verification Methods Are Unsafe
Certain older methods of checking NG tube placement are now considered unreliable and potentially dangerous, and they should never be used as the sole means of verification. The most notable is the auscultation method, which involves injecting air into the tube while listening over the upper abdomen for a “whooshing” sound. This technique is flawed because sound can be transmitted through the chest and abdomen, producing a false “whoosh” even if the tube is coiled in the esophagus or lung.
Research has consistently shown that the auscultation method is highly inaccurate. Relying on this technique can lead to a false sense of security and serious complications if feeding is initiated into a misplaced tube. For this reason, professional organizations recommend the complete abandonment of auscultation for confirming NG tube placement.
Simple visual inspection of the throat or the use of a water bubbling test are also insufficient for confirmation. The bubbling test, where the tube end is placed in water to check for air bubbles, is unreliable because it cannot distinguish between air from the stomach and air from the lungs. Checking for a cough or gag reflex upon insertion is misleading, as these reflexes can be suppressed in ill patients, allowing for silent misplacement into the airway. These clinical signs cannot replace the objective data provided by pH testing or radiographic confirmation.