Using capnography to differentiate airway from gastrointestinal placement of nasogastric tubes: a prospective multicentre diagnostic accuracy study

Background Patient safety incident reports and case reports have repeatedly highlighted factors contributing to inadvertent airway placement of nasogastric tubes, including misleading pH readings, insufficiently documented placement checks, and misinterpretation of radiographs. The study aimed to: (i) evaluate the diagnostic performance of capnography compared with radiography for detecting inadvertent airway placement of nasogastric tubes; and (ii) estimate the average cost incurred when radiography is used alone versus when capnography is used in conjunction with radiography. Methods A multicentre, prospective, observational diagnostic study was conducted. The diagnostic accuracy of capnography was examined using three end-tidal carbon dioxide thresholds (> 5 mmHg, > 10 mmHg, > 15 mmHg), with radiographic confirmation as the reference standard. For each threshold, true positives, false negatives, true negatives, and false positives were determined. Cost savings per patient were estimated using a bias-corrected and accelerated bootstrapping method with 20,000 replications. Results A total of 508 participants were recruited from 39 study sites across 21 hospitals, including medical or geriatric wards, intensive care units, and emergency departments. Most participants ( n = 485; 95.5%) had end-tidal carbon dioxide readings ≤ 5 mmHg. Radiography confirmed correct gastric placement in 452 cases (89.0%), with one case (0.2%) of inadvertent airway placement. Estimated cost savings per patient, were HK$210.3, HK$214.5, and HK$217.5 for the three respective end-tidal carbon dioxide thresholds, based on a hypothetical strategy in which radiographic confirmation was performed only when the end-tidal carbon dioxide value exceeded a predefined threshold, compared with a radiography-only strategy in which all patients underwent radiographic confirmation of nasogastric tube placement. Conclusions Given the favourable outcomes and the simplicity of capnography measurement, capnography can be considered a first-line tool for excluding airway placement of nasogastric tubes, used alongside pH testing of aspirates. Trial registration ClinicalTrials.gov, Number NCT05817864 (Registration date: 18 April 2023).