A nasogastric (NG) tube is a thin, flexible plastic device inserted through the nose and threaded down the throat to reach the stomach. It delivers nutrition, hydration, and medications to patients unable to swallow safely. The tube is also used for gastric decompression, which involves removing air or stomach contents to relieve pressure, nausea, or vomiting. For the tube to function effectively and safely, its tip must be correctly positioned within the digestive system.
The Anatomical Pathway to the Stomach
The tube begins at the naris (nostril) and is guided along the nasal cavity floor into the nasopharynx, then downward into the oropharynx. The pathway separates into the trachea (leading to the lungs) and the esophagus (leading to the stomach).
To ensure correct entry, patients are asked to tuck their chin and swallow water or ice chips as the tube advances past the pharynx. This action elevates the larynx, causing the epiglottis to close over the trachea and directing the tube into the esophagus. The esophagus carries the tube past the diaphragm and into the stomach.
Defining the Target: Correct Placement in the Stomach
The optimal location for the NG tube’s tip is within the stomach, resting in the fundus or the main body. This positioning ensures that delivered contents are introduced well past the gastroesophageal junction (the sphincter separating the esophagus from the stomach). Placing the tip too high risks migration back into the esophagus, leading to inefficient delivery and increased reflux.
The tip must be advanced far enough to prevent coiling in the esophagus, but not so far that it enters the small intestine, unless a nasointestinal tube is intended. Proper positioning suggests the tip should be visible on imaging at least 10 centimeters past the gastroesophageal junction.
To estimate the required length before insertion, the Nose-Ear-Xiphoid (NEX) method is used. This involves measuring the distance from the nose tip to the earlobe, and then down to the xiphoid process (the lower end of the sternum). This external measurement is only an estimate and does not guarantee correct internal placement.
Verifying Location: Confirmation Methods
Since external measurement is only an estimation, confirmation of the tube’s internal location is a mandatory safety step before the tube is used for feeding or medication.
X-Ray Confirmation
The gold standard for initial placement verification is a chest and abdominal X-ray. The X-ray provides a clear image of the tube’s path, confirming that the tip has passed the diaphragm and is correctly positioned in the stomach.
pH Testing
Testing the pH of the fluid aspirated from the tube is another accepted method. Gastric fluid is highly acidic, yielding a pH value between 1 and 5.5, which reliably indicates a stomach location. If the tube is in the respiratory tract, the fluid will be more alkaline, typically with a pH of 6 or higher.
Auscultation
A third method, auscultation, involves injecting a small amount of air through the tube while listening over the stomach area with a stethoscope for a “whoosh” sound. This technique is considered unreliable on its own for confirming placement and is not an accepted primary method for verifying safety. If the pH test is inconclusive or the initial X-ray is unclear, no substance should be administered until the position is definitively confirmed as safe.
Consequences of Misplacement
The most serious risk of improper placement is accidental insertion into the respiratory tract, such as the trachea or a bronchus. If the tube delivers feed or medication while in the lungs, it can lead to severe complications like aspiration pneumonia, a life-threatening infection. In some cases, the tube can puncture the lung, potentially causing a pneumothorax (collapsed lung).
Even if the tube avoids the lungs, a tip that coils in the pharynx or esophagus causes discomfort and renders the tube non-functional. Administering any substance into an unconfirmed tube location is a serious medical error due to the resulting catastrophic outcomes. Consistent and accurate verification steps are paramount to patient safety.