Study to determine the likely accuracy of pH testing to confirm nasogastric tube placement

Rowat, Anne M; Graham, Catriona; Dennis, Martin; Rowat, Anne

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.

Citation

Rowat, A. M., Graham, C., Dennis, M., & Rowat, A. (2018). Study to determine the likely accuracy of pH testing to confirm nasogastric tube placement. BMJ Open Gastroenterology, 5(1), Article e000211. https://doi.org/10.1136/bmjgast-2018-000211

• Journal Article Type: Article
• Acceptance Date: May 14, 2018
• Online Publication Date: Jun 9, 2018
• Publication Date: 2018-06
• Deposit Date: May 23, 2018
• Publicly Available Date: Jun 14, 2018
• Journal: BMJ Open Gastroenterology
• Electronic ISSN: 2054-4774
• Publisher: BMJ Publishing Group
• Peer Reviewed: Peer Reviewed
• Volume: 5
• Issue: 1
• Article Number: e000211
• DOI: https://doi.org/10.1136/bmjgast-2018-000211
• Keywords: nasogastric tube placement, pH testing, gastric aspirates
• Public URL: http://researchrepository.napier.ac.uk/Output/1186436