A prospective observational diagnostic study will be conducted to assess the sensitivity and specificity of ultrasound in verifying the correct nasogastric tube placement, using X-ray as the reference standard.

This study is a prospective observational diagnostic investigation aimed at evaluating the accuracy of ultrasound in confirming nasogastric tube (NGT) placement. Participants aged 18 years or older requiring NGT insertion will be recruited via convenience sampling from community nursing centres across five clusters and medical and geriatric wards in four acute or convalescent hospitals. Nurses performing index tests will complete standardized POCUS training (8-hour theory and practical sessions, written exams, 3-month bedside practicum with ≥20 positive scans) prior to competency assessment. Direct visualisation of an NGT in both the oesophagus and stomach will be interpreted as correct stomach placement. When the acoustic shadow of an NGT was not seen in the stomach, 50cc of air was injected through the NGT, and it was considered well-placed if the ultrasonography showed dynamic fogging. Correct gastric placement is assumed if the acoustic shadow of an NGT is visible in the oesophagus and stomach, even if fogging is not detectable. The reference standard will be post-index test X-ray confirmation. Diagnostic performance metrics, including sensitivity, specificity, positive and negative predictive values, and likelihood ratios, will be calculated to assess the efficacy of ultrasound. Variability in diagnostic accuracy across participant characteristics will be analyzed. Additionally, the study will compare the time intervals between ultrasound and X-ray, delays in feeding initiation post-placement, and associated costs, including emergency department admissions, unplanned hospitalizations, and ambulance transportation.

The findings will provide critical evidence on the diagnostic utility of ultrasound for NGT placement verification, informing potential revisions to clinical practice guidelines and supporting stakeholder decisions on integrating ultrasound as a reference test.

Inclusion Criteria:

• Aged 18 or older;
• Living in the community or admitted to a medical and geriatric ward;
• Requiring the use of an NGT during the recruitment period for assessment, monitoring, nutritional assistance, drainage, and/or medication administration;
• Aspirated fluids with a pH value of more than 5.5 after insertion or with insufficient fluids for pH testing after insertion;

Exclusion Criteria:

• Uncooperative patients;
• Had head and neck injury
• Have had a gastrectomy or by-pass surgery;
• History of abdominal trauma or receiving emergency life support intervention at time of recruitment.

Convenience sampling will be adopted in this study. Participants will be recruited from six community nursing centres in Hong Kong East, Hong Kong West, Kowloon Central, Kowloon West, and New Territories West Cluster hospitals, as well as 38 wards from medical and geriatric wards across 4 acute, rehabilitation or convalescent hospitals managed by the Hospital Authority. Participants will be engaged by episodes throughout the study.

The datasets generated and/or analyzed during this study will be made available by the principal investigator upon reasonable request.