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 (ETCO2) 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. ETCO2 detection by sidestream capnography, which indicates an airway intubation of an NGT when a capnogram waveform or an ETCO2 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 ETCO2 detection as a routine method for verifying NGT placement. TRIAL REGISTRATION: ClinicalTrials.gov ID: NCT05817864.

Photochromism and photopolymerization induced mesophase transitions in mixtures of spiropyran and mesogenic diacrylate.

A phase diagram of a binary mixture of photochromic molecule (spiropyran) and mesogenic diacrylate monomer has been established by means of differential scanning calorimetry and polarized optical microscopy. Subsequently, a theoretical phase diagram has been calculated by self-consistently solving the combined Flory-Huggins free energy for isotropic mixing, Maier-Saupe free energy for nematic ordering, and phase field free energy for crystal solidification. The phase diagram thus obtained consists of various coexistence regions involving single-phase crystals, pure nematic, crystal + liquid, crystal + nematic, and crystal + crystal coexistence gaps. Under UV irradiation, both SP and SP/RM257 mixtures showed the lowering trend of the melting points, which may be attributed to the plasticization effect by the merocyanine isomers. When UV light is illuminated on the 2/98 SP/RM257 mixture for an extended period, mesogenic diacrylate in the mixtures gets polymerized, showing the permanent fixation of isotropic and nematic structures due to the network formation of RM257 caused by the biradicals in the merocyanine intermediate.