Diagnostic Accuracy of Capnography in Nasogastric Tube Placement

A prospective observational diagnostic study will be conducted. Patients ≥ 18-year-old and requiring the insertion of an nasogastric tube will be recruited using a convenience sampling method from general medical and geriatric wards, intensive care units (ICUs), accident and emergency departments (AEDs), and subacute/rehabilitation/infirmary wards in 21 acute or subacute/convalescent/extended care hospitals. End-tidal carbon dioxide (ETCO2) detection by sidestream capnography, which indicates airway intubation of an nasogastric tube when a capnogram waveform or an ETCO2 level \> 10 mmHg, will serve as the index test. The reference standards will be the pH value of gastric content aspiration (pH ≤ 5.5 indicates gastric placement) and X-ray performed after the index test. Each participant will be included only once. Sensitivity, specificity, positive predictive value, and negative predictive value, and the area under the receiver operating characteristic curve of capnography will be calculated to assess the diagnostic performance of capnography. The variability in diagnostic accuracy in participants with different characteristics will be compared. The time spent and the cost of the index test and the reference test will be compared. This study will provide evidence on the diagnostic accuracy of capnography in verifying nasogastric tube placement and inform the update of clinical practice guidelines and stakeholders' decisions regarding the adoption of ETCO2 detection as a routine method for verifying nasogastric tube placement.