Assessing NG tube placement

The ability to safely assess nasogastric (NG) tube placement is a key skill that medical students are required to learn. It is essential that you apply a systematic approach to your assessment and ask for senior input if you have any doubts. Incorrect NG tube placement can result in life-threatening complications and therefore you should take great care when carrying out your assessment. This guide aims to provide you with a systematic approach to confirming safe NG tube placement in your exams, however, it should NOT be used as a guide to confirming NG tube placement on actual patients, instead, you should follow your local hospital guidelines. If you want to learn more about inserting an NG tube you should check out our guide here.

Introduction

There are two main indications for nasogastric (NG) tube insertion:

Nasogastric feeding/administration of medication

Emptying the upper gastrointestinal tract (i.e. small bowel obstruction)

As a doctor, you will inevitably be asked to check and confirm the position of a nasogastric tube before feeding commences.

Complications from misplaced tubes can have serious clinical consequences, including the death of a patient, so you must take great care when assessing NG tube placement.

Anatomy

The oesophagus normally 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).

Anatomical landmarks on a chest x-ray

Methods of confirming NG tube position

Methods that are appropriate to be used for confirming NG tube position include:¹

Measuring the pH of aspirate using pH indicator strips/paper

Radiography (e.g. chest x-ray)

Methods that should NOT be used for confirming NG tube position include:¹

Auscultation of air insufflated through the feeding tube (‘whoosh’ test)

Testing the acidity/alkalinity of aspirate using blue litmus paper

Interpreting the absence of respiratory distress as an indicator of correct positioning

Monitoring bubbling at the end of the tube

Observing the appearance of NG tube aspirate

Testing pH of NG aspirate

After an NG tube has been inserted it is common practice to attempt to obtain an aspirate which then can have its pH checked.

The idea is that gastric contents normally have a low pH (1.5 – 3.5) ² and therefore any aspirate that has a pH this low is likely to be located in the stomach and unlikely to be located elsewhere (e.g. the respiratory tract).

Aspiration can therefore potentially be used as a method for confirming safe NG tube placement without the additional need of a chest x-ray if the pH is within a safe range (0 – 5.5 ).¹

Local guidelines, however, can differ in terms of the acceptable pH range for confirming NG tube placement and some hospitals may require chest x-rays for all patients, regardless of pH aspirate, so always consult your local guidelines.

Limitations of pH testing

1. Stomach pH can be altered by medications (e.g. proton pump inhibitors)

2. Stomach pH can be affected by the frequency of feeds

3. Gaining aspirate from NG tubes can be difficult, particularly when using a fine bore tube

Confirming NG tube position using a chest x-ray

The most accurate method for confirming correct NG tube placement is radiography¹, however despite this there have been multiple reports of x-rays being misinterpreted by doctors leading to patient harm. Radiography is generally not recommended for use routinely, with pH of aspirate suggested as the appropriate first line for confirming safe NG placement if possible (however local policies do differ, so always check your local guidance).

Limitations of using chest x-rays for NG tube placement

1. Potential for misinterpretation

2. Radiation exposure (although minimal)

3. Loss of feeding time

4. Increased handling of unwell patients

5. Access to chest x-rays is difficult in the community

Assessing NG tube placement on a chest x-ray

You should first confirm a few key details:

Check the name, date of birth and unique patient identifier on the x-ray to make sure it matches that of the patient you are assessing

Check the date and time of the x-ray to make sure you are looking at up to date imaging

To confirm an NG tube is placed safely, all of the following key features should be present:

The chest x-ray view should be adequate – upper oesophagus down to below the diaphragm

The NG tube should remain in the midline down to the level of the diaphragm

The NG tube should bisect the carina (T4)

The tip of the NG tube should be clearly visible and below the diaphragm

The tip of the NG tube should be 10 cm beyond the GOJ to be confident that it’s within the stomach

If any of the above features are not present, or you have any doubt about the placement of the NG tube you should discuss the situation with radiology who may provide an expert opinion on the imaging or arrange further contrast studies to confirm safe placement.

Things to be aware of:

An NG tube can be placed in the left or right main bronchus but to still appear in the midline (hence why 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 (this is relatively common) which can potentially result in reflux and aspiration of NG tube contents. This demonstrates the importance of confirming you can see the NG tube tip clearly, as you cannot confirm safe placement of an NG tube without knowing where the tip is.

Example of correct NG tube placement

The example below meets the criteria of safe NG placement mentioned previously:

The chest x-ray view is adequate – upper oesophagus down to below the diaphragm

The NG tube remains in the midline down to the level of the diaphragm

The NG tube bisects the carina (T4)

The tip of the NG tube is clearly visible and below the diaphragm

The tip of the NG tube is at least 10 cm beyond the GOJ and therefore within the stomach

Correctly placed NG tube (Source: Wikiradiography.net) 3

Examples of incorrect NG tube placement

NG tube placed in left and right main bronchus

This chest x-ray shows the NG tube has entered the trachea, then entered the left main bronchus and then coiled backwards over into the right main bronchus where the tip can be seen lying.

If we assess this x-ray using the criteria for safe placement it is clear that it would not be possible to deem the placement as safe:

The chest x-ray view is adequate – YES

The NG tube remains in the midline down to the level of the diaphragm – NO

The NG tube bisects the carina (T4) – NO

The tip of the NG tube is clearly visible and below the diaphragm – NO

The tip of the NG tube is at least 10 cm beyond the GOJ and therefore within the stomach – NO

Example of NG tube in right main bronchus (Source: Wikiradiography.net)3

NG tube placed in left lung

This 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 mean it is in the gastrointestinal tract.

If we assess this x-ray using the criteria for safe placement it is clear that it would not be possible to deem the placement as safe:

The chest x-ray view is adequate – YES

The NG tube remains in the midline down to the level of the diaphragm – NO

The NG tube bisects the carina (T4) – NO

The tip of the NG tube is clearly visible and below the diaphragm – NO

The tip of the NG tube is at least 10 cm beyond the GOJ and therefore within the stomach – NO

NG tube in left lung (Source: Wikiradiography.net)3

Inadequate insertion length

This chest x-ray shows an NG tube that has been inserted into the oesophagus successfully, but has not been inserted to an adequate length. As a result, although the tip of the NG tube is likely to be within the fundus of the stomach, the side hole where the feed is excreted is most likely still within the oesophagus. NG tubes not placed to an adequate length can result in oesophageal reflux of feed and potentially aspiration of feed. This NG tube would need inserting further and re-assessing with an x-ray to ensure placement was adequate.

If we assess this x-ray using the criteria for safe placement it is clear that it would not be possible to deem the placement as safe:

The chest x-ray view is adequate – YES

The NG tube remains in the midline down to the level of the diaphragm –YES

The NG tube bisects the carina (T4) – YES

The tip of the NG tube is clearly visible and below the diaphragm – YES

The tip of the NG tube is at least 10 cm beyond the GOJ and therefore within the stomach – NO

NG tube not inserted to an adequate length (Source: Wikiradiography.net)3

Difficult to see NG tube tip

Sometimes on the ward it is very difficult to see 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 safe placement it is clear that it would not be possible to deem the placement as safe:

The chest x-ray view is adequate – YES

The NG tube remains in the midline down to the level of the diaphragm –YES

The NG tube bisects the carina (T4) – YES

The tip of the NG tube is clearly visible and below the diaphragm – NO

The tip of the NG tube is at least 10 cm beyond the GOJ and therefore within the stomach – NO

NG tip not clearly visible & multiple lines (Source: Wikiradiography.net)3

If you were unable to see the tip of an NG tube you should speak with the radiologist who may:

Repeat the CXR (possibly with another view e.g. lateral)

Inject water-soluble contrast then take repeat x-rays to see if contrast pools within the stomach or oesophagus

Presenting a chest x-ray for NG tube confirmation

If asked to present your findings make sure to mention all the key criteria you have assessed to confirm the NG tube placement is safe:

“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 diaphragm and is at least 10cm beyond the gastro-oesophageal junction. I can confirm that this tube is in a safe position to commence feeding”.