Diagnostic accuracy of using capnography in verification of nasogastric tube placement among adult patients in hospital settings: Protocol of a diagnostic study

OBJECTIVE: To determine the diagnostic accuracy of end-tidal carbon dioxide (ETCO(2)) detection using capnography for verifying the correct placement of nasogastric tubes (NGTs) among adult patients in hospital settings. MATERIALS AND METHODS: A prospective observational diagnostic study will be conducted. Patients ≥ 18-year-old and requiring the insertion of an NGT will be recruited using a convenience sampling method from 39 general medical and geriatric wards, intensive care units, accident and emergency departments, and subacute/rehabilitation/infirmary wards in 21 acute or subacute/convalescent/extended care hospitals. ETCO(2) detection by sidestream capnography, which indicates an airway intubation of an NGT when a capnogram waveform or an ETCO(2) level > 10mmHg (1.33 kPa) occurs, will serve as the index test. The reference standards will be the X-ray performed and pH value of gastric aspiration (pH ≤ 5.5) after the index test. Each participant will be included only once. Sensitivity, specificity, positive predictive value, negative predictive value, and 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 explored by using chi-squared or Fisher’s exact tests. The time spent and the cost of the tests will be compared using the paired t-test. All statistical tests will be two-sided with a level of significance set at 0.05. DISCUSSION: This study will provide evidence on the diagnostic accuracy of capnography in verifying NGT placement and its applicability to patients in hospitals settings, since this evidence is limited in the current literature. In addition, it will help identify the optimal combination of tests in verifying the correct placement of NGTs and inform the update of clinical practice guidelines and stakeholders’ decisions on the adoption of ETCO(2) detection as a routine method for verifying NGT placement. TRIAL REGISTRATION: ClinicalTrials.gov ID: NCT05817864.