A malpositioned nasogastric tube, improper feeding site, large gastric volume and supine position are the main risk factors for aspiration during enteral feeding. When enteral formulations or medications enter the lung through a nasogastric tube inadvertently positioned in the respiratory tract, the life-threatening complication that results is referred to as “aspiration by proxy” (Figure 1).1 Show Auscultation is most often used at the bedside to check for appropriate placement of a nasogastric tube. Sound generated by air blown through the tube is used to determine tube placement in the gastrointestinal tract. However, a similar gurgling can be heard over the epigastrium when the tube has been incorrectly placed into the tracheobronchial tree, pleural space or esophagus.2,3 Aspirate from a tube placed in the stomach is usually grassy green or colourless, with shreds of off-white to tan mucus. The aspirate often has a pH of 5 or less. In the absence of infection, respiratory secretions are usually clear. However, measuring the pH level alone does not differentiate between respiratory and gastrointestinal placement of the tube; both sites can have high pH values (> 6).4 The pH test has no value if the patient is receiving acid suppression medication. In situations where the patient may have suppressed gag or cough reflexes (e.g., decreased level of consciousness or neurologic debilitation), the absence of coughing or choking after placement of the tube may be misleading. Research continues into simple bedside methods for determining appropriate placement of nasogastric tubes. An abdominal radiograph is considered the “gold standard” for determining the position of a nasogastric tube, especially in a critically ill, elderly, dysphagic or unconscious patient.5 “Five things to know about …” is a new series that presents key statements on topics of interest to physicians. For author instructions, go to cmaj.ca. Previously published at www.cmaj.ca Competing interests: None declared. This article has been peer reviewed. Articles from CMAJ : Canadian Medical Association Journal are provided here courtesy of Canadian Medical Association
The ability to safely assess nasogastric (NG) tube placement is a key skill that medical students need to develop. The assessment of NG tube placement requires a systemic approach and a willingness to ask for senior assistance if unsure, to prioritise patient safety. The incorrect placement of an NG tube can result in life-threatening complications (e.g. aspiration pneumonia). This guide aims to provide you with a systematic approach to confirming safe NG tube placement in an OSCE setting and should NOT be relied upon outside of this setting (always follow local guidelines).
To learn about how to insert an NG tube, check out our OSCE guide. Indications for NG tube insertionThe most common indications for NG tube insertion include:
When inserting an NG tube for feeding and/or administration of medication you need to confirm the safe placement of the tube prior to its use. The incorrect placement of an NG tube can result in life-threatening complications (e.g. aspiration pneumonia). Methods of confirming NG tube positionThe two methods of confirming NG tube position include:¹
Methods which should never be used to confirm NG tube position include:¹
Testing pH of NG aspirateConfirmation of safe NG tube placement can be achieved by testing the pH of NG tube aspirate. Gastric content has a low pH (1.5-3.5) whereas respiratory tract secretions have a much higher pH.² This difference makes it possible to confidently confirm the safe placement of an NG tube using pH testing alone if the pH is within a safe range (typically 0 – 5.5).¹ The acceptable pH range for confirming NG tube placement can differ, so always follow your local medical school and/or hospital guidance. In addition, some hospitals may require a chest X-ray to confirm the safe placement of all NG tubes, regardless of the NG aspirate results, so always consult your local guidelines. Some limitations of pH testing include
You might also be interested in our OSCE Flashcard Collection which contains over 2000 flashcards that cover clinical examination, procedures, communication skills and data interpretation. Confirming NG tube position using a chest X-rayIf pH testing of NG aspirate is not possible, a chest X-ray can be used to confirm the safe placement of an NG tube. Limitations of using a chest X-ray to confirm safe NG tube placement include:
Anatomical landmarks on a chest X-rayIt is essential that you can recognise key anatomical landmarks on a chest X-ray if you are to safely confirm NG tube placement using this imaging modality. The annotated chest X-ray below highlights these key anatomical landmarks including:
The oesophagus itself is often difficult to directly visualise on chest X-ray. It typically lies to the left of the trachea and medially to the aortic knuckle. The normal oesophagus passes through the diaphragm and enters the stomach at the gastroesophageal junction (GOJ). Assessing NG tube placement on a chest X-rayConfirm key X-ray detailsYou should first confirm a few key details including:
Confirm safe placement of the NG tubeTo confirm an NG tube is positioned safely, all of the following criteria should be met:
If any of the above criteria are not met and/or you have any doubt about the placement of the NG tube you should seek advice from a senior colleague or discuss with the on-call radiologist. Incorrect placement of an NG tubeAn NG tube can be positioned in the left or right main bronchus but to still appear in the midline (hence why the single criterion of an NG tube appearing in the midline is not satisfactory evidence to confirm safe placement). An NG tube can curl up on itself, meaning the tip is placed higher than it should be which can result in reflux and aspiration of NG tube contents. This demonstrates the importance of confirming you can see the NG tube tip clearly. Example of correct NG tube placementThe example below meets the criteria of safe NG placement mentioned previously:
Examples of incorrect NG tube placementNG tube placed in the left and right main bronchusThis chest X-ray shows an NG tube which has entered the trachea, then the left main bronchus before finally coiling backwards on itself over into the right main bronchus where the tip can be seen. If we assess this X-ray using the criteria for correct NG tube placement it is clear that it would not be possible to deem this placement as safe:
NG tube placed in the left lungThis chest X-ray demonstrates an NG tube that has entered the trachea, then entered the left main bronchus and then penetrated through the left lung parenchyma and visceral pleural. The NG tube tip has therefore ended up in the pleural space (with an associated pneumothorax). This is an extreme example of misplacement, but it is a good example of why an NG tube tip appearing close to or slightly below the diaphragm alone does not confirm it is in the gastrointestinal tract. If we assess this X-ray using the criteria for correct NG tube placement it is clear that it would not be possible to deem this placement as safe:
Inadequate insertion lengthThis chest X-ray shows an NG tube that has been inserted into the oesophagus successfully but to an inadequate length. As a result, although the tip of the NG tube is likely to be within the fundus of the stomach, the aperture through which feed is excreted is most likely still within the oesophagus. NG tubes which are not inserted to an adequate length can result in oesophageal reflux of feed and potentially aspiration. This NG tube would need inserting further and re-assessing with a repeat X-ray to ensure placement was adequate. If we assess this X-ray using the criteria for correct NG tube placement it is clear that it would not be possible to deem this placement as safe:
Difficult to see NG tube tipSometimes it is very difficult to visualise the NG tube tip and additional wires and/or lines can make the image even harder to interpret, as the example below demonstrates. If we assess this X-ray using the criteria for correct NG tube placement it is clear that it would not be possible to deem this placement as safe:
If the tip of an NG tube is not clearly visible, you should discuss with the on-call radiologist who may advise:
We have provided an example of how you might present your findings after reviewing the position of an NG tube on a chest X-ray. “This is an AP chest radiograph of an adult [male/female]. The chest X-ray view is adequate and the NG tube can be seen bisecting the carina and remaining in the midline to the level of the diaphragm. The tip of the nasogastric tube is visible below the left hemidiaphragm and is 10cm beyond the gastro-oesophageal junction. Based on these findings, I feel the NG tube is positioned safely.” References
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