Chapter 8: Nutrition and fluid balance
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Nasogastric tube insertion
Evidence‐based approaches
Rationale
It is essential that the position of the nasogastric tube is confirmed prior to feeding to ensure that it has been placed safely in the gastrointestinal tract and has not been inadvertently placed in the lungs. Inadvertent placement of the tube would result in the risk of fluid or feed being administered to the lungs – a potentially life‐threatening situation.
Indications
Nasogastric tube insertion is indicated for patients who require short‐term enteral tube feeding (2–4 weeks) as a sole source of nutrition or for supplementary feeding.
Contraindications
Nasogastric tube insertion is contraindicated for:
- patients who require long‐term enteral tube feeding, in whom it may be more appropriate to use a gastrostomy tube
- patients with an altered anatomy that would make it impossible to pass a nasogastric tube comfortably.
Careful consideration should also be given to patients with coagulation disorders, who should have their blood clotting checked by the medical team and appropriate blood products administered if required prior to insertion.
Anticipated patient outcomes
The patient has a nasogastric tube inserted comfortably and safely. The position is checked and it is confirmed that the tube is placed in the stomach.
Clinical governance
In law, enteral feeding is regarded as a medical treatment and should therefore not be started without considering all related ethical issues. Valid consent to treatment is essential in the placement of enteral feeding tubes.
In the management of those with an eating disorder, feeding against their will should be a last resort. It should be considered in the context of the Mental Health Act ([100]), the Mental Capacity Act ([99]) and the Children Act ([34]) (and their respective Codes of Practice), as appropriate.
Where the Mental Capacity Act ([99]) is used to authorize enteral feeding, the patient should be assessed to see whether additional authorization is required under the Deprivation of Liberty Safeguards. All mental capacity assessments must be Mental Capacity Act compliant.
Those passing a nasogastric tube should have achieved competencies set by the local trust (NHSI [116], NNNG [128]). Introduction of fluids or medication into the respiratory tract or pleura via a misplaced nasogastric or orogastric tube is a ‘Never Event’ (NHS England [114]). Placement devices for nasogastric tube insertion do not replace initial position checks (NHS England [112]). All equipment used to support enteral feeding should be ENFit compliant (see the section above on ENFit) (NHSI [117]). Documentation of enteral tube placement should be rigorous and in line with local policy (e.g. care bundles or passport). Such documentation may include pre‐insertion assessments, date and time of insertion, appropriate monitoring post‐insertion and guidance for healthcare professionals on post‐insertion care.
Pre‐procedural considerations
Specific patient preparation
The planned procedure should be discussed with the patient so that they are aware of the rationale for the insertion of a nasogastric tube. The decision to insert a nasogastric tube must be made by at least two healthcare professionals, including the senior doctor responsible for the patient's care. Verbal consent for the procedure must be obtained from the patient if they are conscious and able to give it.
Prior to performing this procedure, the patient's medical and nursing notes should be consulted to check for potential complications. For example, anatomical alterations due to surgery, such as a flap repair, or the presence of a cancerous tumour or nasal polyps can prevent a clear passage for the nasogastric tube, resulting in pain and discomfort for the patient and further complications such as bleeding or tissue damage. Patients who have recurrent retching or vomiting, have swallowing dysfunction or are comatose have a high risk of placement error or migration of the tube so care must be taken when placing a nasogastric tube under these circumstances (NHSI [116]). It may be more appropriate for such patients to have a nasojejunal tube placed endoscopically to reduce the risks of vomiting, regurgitation and potential aspiration of feed, and tube misplacement. The assessment of the patient, the risks and the obtained patient consent should be clearly documented.
Social and psychological impact
For some patients a nasogastric tube can be distressing. This is not only due to physical discomfort but also perceptions of body image, particularly as this type of feeding tube is highly visible. Some people find that the tube limits their social activity due to embarrassment, which can lead to feelings of isolation. Others see it as a reminder of ill health, which can have an impact on mood. These issues should be discussed with the patient prior to tube insertion.
Procedure guideline 8.10
Nasogastric intubation with tubes using an internal guidewire or stylet
Table 8.14 Prevention and resolution (Procedure guideline 8.10)
| Problem | Cause | Prevention | Action |
|---|---|---|---|
| Unable to place the nasogastric tube |
The patient has altered anatomy.
The patient is distressed or not compliant with the procedure. |
Seek expert help for any altered anatomy
Ensure the procedure is fully explained to the patient and try and reassure them as much as possible. | The nasogastric tube should be placed under X‐ray guidance or via endoscopy. |
| Unable to obtain aspirate from the nasogastric tube | The tip of the tube is not sitting in gastric contents, is against the stomach wall or is not advanced sufficiently into the stomach. | Measure the tube correctly as shown in Procedure guideline 8.10 Action figure 8.27. | See Box 8.6. |
| A pH of greater than 5.5 is obtained | The nasogastric tube may be placed in the lungs. The patient may be on acid‐inhibiting medication and this may contribute to a higher gastric pH. | Check the pH of the gastric aspirate just before the time of administration of acid‐inhibiting medication, when gastric pH is likely to be at its lowest. | If initial confirmation cannot be obtained from pH aspirate then the tube may need to be X‐rayed as it may be in the lungs. |
| Initial correct placement is confirmed but subsequently unable to obtain an aspirate | The nasogastric tube may not be positioned in gastric contents or may have become misplaced. | Check the length of tube against the NEX measurement; then, using the NEX measurement as a reference point, advance or withdraw the tube by 5–10 cm. Give mouth care to patients who are nil by mouth (this stimulates the secretion of gastric acid). Try and obtain an aspirate again (BAPEN [10]). | Undertake risk assessment and document action. The nasogastric tube may need to be repositioned and rechecked with an X‐ray. |
Box 8.6
Methods to obtain an aspirate from a nasogastric tube
Try the following either one at a time or in combination:
- Turn patient onto their left side.
- Inject 10–20 mL of air (do not use water to flush the tube until the position has been confirmed) into the tube using a 60 mL ENFit syringe; wait 15–30 minutes.
- Advance or withdraw the tube by 10–20 cm.
- Check the NEX measurement and external length to assess whether the tube has moved (advance the tube 5–10 cm over NEX measurement if safe to do so).
- Provide mouth care (doing so may stimulate the secretion of gastic acid).
- Then try aspirating again.
Post‐procedural considerations
Immediate care
The position of the nasogastric tube must be checked at initial placement and again prior to the administration of all medication and feeds. Failure to confirm the position of the tube in the stomach can lead to the administration of fluid, medication or feed directly into the lungs, resulting in aspiration pneumonia.
The position of the nasogastric tube can be checked using two methods:
- First‐line method: testing of gastric aspirate with pH indicator paper: the use of pH to check the position of the tube is based on an understanding of the pH of body fluids, particularly gastric contents, and the pH scale (Box 8.7). This should have a pH less than 5.5 (NHSI [116]).
- Second‐line method: X‐ray: an X‐ray must be used to confirm the position of the tube in patients for whom it has not been possible to confirm the position of the tip of the nasogastric tube by gastric aspirate and pH indicator strips. The X‐ray must be read by medical staff with appropriate training and competence (NHSI [116]).
See Procedure guideline 8.10 for details on how to conduct these tests.
Box 8.7
The clinical importance of the pH scale
The pH scale is a convenient way of recording large ranges of hydrogen ion concentrations without using the cumbersome numbers that are needed to describe the actual concentrations. That is why each step down the scale is a 10‐fold increase in acidity (or a 10‐fold decrease if going up the scale). This means that stomach contents of pH 5 have 10 times more acidity than lung fluid of pH 6. Not knowing this could place a patient in harm's way.
The midpoint of the scale is 7. This number is related directly to the actual concentration of hydrogen ions in water, which is one ten‐millionth units per litre – an extremely small number. One ten‐millionth is the same as 1 divided by 107. So a liquid of pH 6 has one‐millionth units per litre – that is, 1 divided by 106 – and has 10 times the concentration of hydrogen ions as does pure water. This example shows why as the pH decreases, the hydrogen ion concentration, and thus the acidity, increases. For example, lemon juice and vinegar are acidic with pHs of 2.2 and 3 respectively, whereas bleach is alkaline with a low concentration of hydrogen ions and a pH of 11.
In the body, the pH of cells, body fluids and organs is usually tightly controlled in a process called ‘acid‐base homeostasis’. Without this careful regulation of pH or ‘buffering’, the normal body chemistry processes cannot take place successfully and illness, or in extreme cases death, can occur (Aoi and Marunaka [4]).
The pH of blood is slightly basic (slightly more alkalotic than acidic), with a value of 7.4, whereas gastric acid can range from 5.5 to the highly acidic 0.7 and pancreatic secretions are measured at 8.1. When the pH in the body decreases – that is, it becomes more acidic – ‘acidosis’ can occur, leading to symptoms such as shortness of breath, muscular seizure and coma.
pH also influences the structure and function of many enzymes in living systems. These enzymes usually only work satisfactorily within narrow pH ranges. Thus, pepsin, a stomach enzyme, works best at pH 2. In the duodenum, trypsin functions best at around pH 7.5–8.0. Generally, most human cell enzymes work best in a slightly alkaline medium of about 7.4.
Keeping the cellular pH at the correct level is very important. In the case of unregulated diabetes, high blood sugar levels occur, leading to acidic conditions that rapidly destroy enzymes and cells. Consequently, regular blood sugar monitoring is crucial for diabetics.
In living systems, pH is therefore more than just a measure of hydrogen ion concentration as it is critical to life and the many biochemical reactions that have to take place to maintain a person in optimum health.
In accordance with NHS Improvement guidance, the following methods are outdated and unreliable, and should not be used to confirm the position of a feeding tube (NHSI [116]):
- auscultation of air insufflated through the feeding tube (‘whoosh test’)
- testing the pH of the aspirate using blue litmus paper
- interpreting the absence of respiratory distress as an indicator of the correct positioning
- monitoring bubbling at the end of the tube
- observing the appearance of feeding tube aspirate
- use of placement devices for nasogastric tube insertion.
In addition to the initial confirmation, the tube should be checked on a daily basis if not in use and/or prior to the administration of any medication or feed (see ‘Ongoing care’ below for further details).
When the nasogastric tube is confirmed to be in the stomach, a mark should be made on the tube at the exit site from the nostril with a permanent marker pen. The length of tube visible from the exit of the nostril to the end of the tube should be measured in centimetres and recorded along with the NEX measurement. This is to help detect whether the nasogastric tube has become displaced. See Figure 8.28 for an X‐ray of a correctly inserted nasogastric tube, Figure 8.29 for information on test precision and test risk when checking the position of a nasogastric tube, and Figure 8.30 for checks to carry out when using pH indicator sticks.
Figure 8.28 X‐radiograph of a correctly inserted nasogastric tube. Source: Reproduced from PPSA ([147]) with permission of the ECRI Institute (ecri.org.uk).
Figure 8.29 Test precision and test risk: the connection. Source: Reproduced from PPSA ([147]) with permission of the ECRI Institute (ecri.org.uk).
Figure 8.30 Four key checks to carry out when using the pH tests. Source: Reproduced with permission of the ECRI Institute (www.ecri.org.uk) and The Royal Marsden NHS Foundation Trust.
Ongoing care
Once the nasogastric tube has been confirmed to be in the stomach and the guidewire or stylet removed, feeding may commence. The tube should be kept patent by regular flushing before and after administering feed and medication. Preferably only liquid medication should be used as tablets may block the lumen of the tube (BAPEN [13]). Tablets should only be used if no alternative liquid or soluble preparation is available, and they should be crushed before administration. Always check with a pharmacist as some medication should not be crushed. See also Procedure guideline 8.16: Jejunostomy feeding tube care including dressing change.
The position of the tube must be verified by checking the pH of aspirate from the tube and recorded on a chart kept at the patient's bedside (NHSI [116]):
- before administering each feed
- before giving medication
- following episodes of vomiting, retching or coughing as it is likely the tube will have become displaced
- following evidence of tube displacement (e.g. the measured length of the tube is longer).
If a pH of below 5.5 is not obtained then it is highly likely that the tube has become displaced. The medical team should be contacted as the tube may need to be replaced. For further details on checking nasogastric tubes, refer to the full NHS Improvement guidance or local policy (NHSI [116]).
Education of the patient and relevant others
If appropriate, the patient may be taught how to check the position of the nasogastric tube. They should be made aware that if they feel the tube has moved, it must not be used for feeding or medication administration until its position has been confirmed by one of the methods described.
Complications
Nasal erosion
Prolonged nasogastric feeding or use of a wide‐bore tube can lead to nasal erosion (NNNG [128]). To reduce the risk of this occurring, it is important to use appropriate tape and assess the skin in this area on a regular basis. If erosion occurs, it is advised that the tube is removed and replaced in the other nostril. If feeding is to be long term then a gastrostomy or jejunostomy should be considered.
Displacement of tube
A tube can accidentally be pulled out or displaced, particularly if a patient is restless or distressed. It can also be coughed or vomited out of place. In this situation the position of the tube should be checked. If it is not possible to confirm that the tube remains within the stomach then it should be removed and a new tube placed (NHSI [116]).
