Diagnostic accuracy of a pH stick, modified to detect gastric lipase, to confirm the correct placement of nasogastric tubes

Rowat, A. M. , Graham, C. and Dennis, M. (2018) Diagnostic accuracy of a pH stick, modified to detect gastric lipase, to confirm the correct placement of nasogastric tubes. BMJ Open Gastroenterology, 5(1), e000218. (doi: 10.1136/bmjgast-2018-000218) (PMID:30116546) (PMCID:PMC6089299)

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Objective: The correct placement of a nasogastric feeding tube is usually confirmed by establishing that an aspirate is acidic using a pH stick. However, antacid medication and achlorhydria can cause false negative pH tests that may delay feeding and increase resource use. The purpose of this study was to evaluate a modified pH stick designed to detect gastric lipase and therefore reduce false negative tests. Methods: In this prospective observational study, a convenience sample of adult patients who had either gastric and oesophageal samples taken during routine diagnostic gastroscopy (n=97) or bronchial and saliva samples taken during a bronchoscopy (n=106). The samples were tested by blinded observers using the modified and standard pH sticks. The sensitivities and specificities of the two pH sticks in identifying gastric and non-gastric aspirates were compared using the pH cut-off ≤5.5. Results: The sensitivities of a pH≤5.5 to correctly identify gastric samples were 66% (95% CI 56 to 75) and 68% (95% CI 57 to 77) for the modified and the standard pH, respectively. The specificities were 81% (95% CI 76 to 85) and 79% (95% CI 74 to 84). There were no significant differences in the distribution of the discordant results between the paired gastric and non-gastric samples for both the modified and standard pH sticks at pH≤5.5 (both McNemar’s tests, p≥0.05). Conclusions: There were no significant differences between the paired modified and standard pH tests for the gastric samples. Due to the limited accuracy of pH sticks, further research is required to identify accurate and cost-effective bedside methods to confirm the correct placement of nasogastric tubes.

Item Type:Articles
Additional Information:Funded by internal funding from the Centre for Clinical Brain Sciences, University of Edinburgh.
Glasgow Author(s) Enlighten ID:Rowat, Dr Anne
Authors: Rowat, A. M., Graham, C., and Dennis, M.
College/School:College of Medical Veterinary and Life Sciences > School of Medicine, Dentistry & Nursing > Nursing and Health Care
Journal Name:BMJ Open Gastroenterology
Publisher:BMJ Publishing Group
ISSN (Online):2054-4774
Published Online:31 July 2018
Copyright Holders:Copyright © 2018 The Authors
First Published:First published in BMJ Open Gastroenterology 5(1): e000218
Publisher Policy:Reproduced under a Creative Commons License

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