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Endoscopy
Study to determine the likely accuracy of pH testing to confirm nasogastric tube placement
  1. Anne M Rowat3,
  2. Catriona Graham1,
  3. Martin Dennis2
  1. 1 Edinburgh Clinical Research Facility, University of Edinburgh, Edinburgh, UK
  2. 2 Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, UK
  3. 3 School of Health and Social Care, Edinburgh Napier University, Edinburgh, UK
  1. Correspondence to Dr Anne M Rowat; a.rowat{at}napier.ac.uk

Abstract

Objective To establish the likely accuracy of pH testing to identify gastric aspirates at different pH cut-offs to confirm nasogastric tube placement.

Methods This prospective observational study included a convenience sample of adult patients who had two (one fresh and one frozen) gastric and oesophageal samples taken during gastroscopy or two bronchial and saliva samples taken during bronchoscopy. The degree of observer agreement for the pH of fresh and frozen samples was indicted by kappa (k) statistics. The sensitivities and specificities at pH ≤5.5 and the area under the receiver operating characteristics (ROC) curve at different pH cut-offs were calculated to identify gastric and non-gastric aspirates.

Results Ninety-seven patients had a gastroscopy, 106 a bronchoscopy. There was complete agreement between observers in 57/92 (62%) of the paired fresh and frozen gastric samples (k=0.496, 95% CI 0.364 to 0.627). The sensitivity of a pH ≤5.5 to correctly identify gastric samples was 68% (95% CI 57 to 77) and the specificity was 79% (95% CI 74 to 84). The overall accuracy to correctly classify samples was between 76% and 77%, regardless of whether patients were taking antacids or not. The area under the ROC curve at different pH cut-offs was 0.74.

Conclusion The diagnostic accuracy of pH ≤5.5 to differentiate gastric from non-gastric samples was low, regardless of whether patients were taking antacids or not. Due to the limited accuracy of the pH sticks and the operators’ ability to differentiate colorimetric results, there is an urgent need to identify more accurate and safer methods to confirm correct placement of nasogastric tubes.

  • gastroscopy
  • endoscopy
  • pH monitoring

This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/

https://doi.org/10.1136/bmjgast-2018-000211

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    Footnotes

    • Contributors All authors approved the final version of the manuscript. Study concept and design: MD, CG and AMR. Statistical analysis: CG. Acquisition, analysis and interpretation of data: AMR, CG and MD. Drafting of the manuscript: AMR, CG and MD.

    • Funding The study was funded by internal funding from the Centre for Clinical Brain Sciences, University of Edinburgh.

    • Competing interests None declared.

    • Patient consent Not required.

    • Ethics approval This study received prior approval from the Lothian NHS Research Ethics Committee (REC: 13/SS0184; R&D: 20130299).

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Data sharing statement The deidentified data set will be made available on request to the lead author.