The primary indications for nasogastric (NG) tube insertion are:
• To aspirate stomach contents for diagnostic or therapeutic purposes.
• Gastrointestinal bleeding.
• Determination of gastric acid content.
• Treatment of paralytic ileus.
• Intestinal obstruction.
• To provide a route for feeding or administration of medications.
Checking the position of the tube can be done by many different methods:
Auscultation technique: 30-60 cc of air is injected through the NG tube while the abdomen is ausculated, the act of listening to sounds made by internal organs. If the tube is in the stomach, the passage of air should be heard by placing a stethoscope over the stomach. Although useful, this method has been shown to be unreliable.
Aspiration of gastric contents: Gastric contents are aspirated and visually inspected. Again, this method is not reliable; pleural fluid can, at times, take on the appearance of gastric contents.
pH testing: Gastric contents are aspirated and the pH level is checked. Gastric fluid has a pH of 1 to 4; intestinal fluid has a pH of 6 to 7. Unfortunately, there is not much quality research that addresses the accuracy of this method.6 As well, the pH of the gastric content aspirated can vary due to medications, age, and gender, also the test itself is subjective when it is done using litmus paper.
Carbon dioxide measuring: There are several ways to check for carbon dioxide in the NG tube. Capnometry is simple and appears to be very accurate.8 In this method, an end-tidal carbon dioxide detector is attached to the proximal end of the nasogastric tube and the presence (or absence) of carbon dioxide can be confirmed. This test is limited by the availability of the equipment.
Water testing: The proximal end of the tube can be submerged in water, and if bubbling is seen, this may be an indication that the tube is in the lung. However, this method cannot be relied on to affirm proper tube placement.
Magnet tracking: A small magnet is affixed to the distal end of the nasogastric tube prior to insertion and the position of the tube is ascertained by an external sensor array attached to a computer. One author notes this technique to be 100% reliable. Again this technique is limited by the availability of the equipment.
Abdominal radiograph: An abdominal radiograph that includes the fundus of the stomach may be taken to confirm proper tube placement.
– Nasogastric tube insertion University of Ottawa. Department of Emergency Medicine. Nasogastric Tube Insertion