The Royal Marsden Hospital Manual of Clinical Nursing Procedures - Lisa Dougherty [274]
These tests are not accurate or reliable as a method of checking the position of a nasogastric tube as they have been shown to give false-positive results (Metheny and Meert 2004, E; NPSA 2005, C).
14 Document the tip position in the patient’s notes.
To record the position (NMC 2009, C).
Problem-solving table 8.3 Prevention and resolution (Procedure guidelines 8.10 and 8.11)
Postprocedural considerations
Immediate care
The position of the nasogastric tube must be checked at initial placement and again prior to the administration of all medication or feed. 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 (Figure 8.4).
Figure 8.4 How to confirm the correct position of nasogastric feeding tubes in adults (NPSA 2005). Used with permission of the NPSA. For updates see www.npsa.nhs.uk.
The position of the nasogastric tube can be checked using two methods.
Chest X-ray. A chest X-ray must be used to confirm the position of the tube in high-risk groups such as patients with oesophageal or head and neck tumours, those who have impaired swallowing or who are unconscious, because they are at higher risk of misplacement of the nasogastric tube.
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 (see Box 8.3). All patients who do not require an X-ray should have the position of the tube checked with syringed aspirate of gastric content. This should have a pH less than 5.5 (NPSA 2005).
In accordance with NPSA guidance, the following methods should not be used to confirm the position of a feeding tube.
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.
Box 8.3 The clinical importance of the pH scale
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 (or a 10-fold decrease if going upscale) in the acidity. This means that stomach contents of pH 5 have 10 times as much acidity as has lung fluid of pH 6. Not knowing this could place your 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 one 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, increase. For example lemon juice and vinegar are acidic with a pH 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 homoeostasis. Without this careful regulation of pH or buffering, the normal body chemistry cannot take place successfully and illness or in extreme cases death can occur.
The pH of blood is slightly basic 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 becomes more