Diagnostic accuracy of methods used to verify nasogastric tube position in mechanically ventilated adult patients: a systematic review.

Background: Nasogastric tubes are widely used in hospitals, e.g. for the administration of nutrients. However, nasogastric tubes can be inserted accidently into the airways leading to complications like pneumonia, pneumothorax and even death. Mechanically ventilated patients are at high risk of having a nasogastric tube misplaced, since they often have reduced consciousness and weak cough reflex. A variety of methods have been used for determination of nasogastric tube placement, but with varying success.

Objectives: The present systematic review was carried out to evaluate the diagnostic accuracy of methods used to determine nasogastric tube placement in mechanically ventilated adult patients.

Inclusion Criteria: Studies including mechanically ventilated adult patients with a nasogastric tube were considered for inclusion, regardless of the type of nasogastric tube.All methods (index tests) used to verify nasogastric tubes placed in the airways and in the gastrointestinal tract were included. As a reference standard, X-ray was used to verify the accuracy of each index test.The studies that were included in the present systematic review were designed based on diagnostic test accuracy studies.The outcome was the accuracy (sensitivity and specificity) of the methods to discriminate between respiratory and gastrointestinal placement of the nasogastric tube.

Search Strategy: The search strategy aimed to find both published and unpublished studies before September 2013. Eleven electronic databases were searched including CINAHL, PubMed, Scopus and Embase.

Methodological Quality: Methodological quality was assessed independently by two reviewers using QUADAS as a critical appraisal tool.

Data Extraction: Data were extracted by two reviewers independently using a modified Joanna Briggs Institute data extraction form including specific details such as: population, setting, index test, sensitivity and specificity.

Data Synthesis: Sensitivity and specificity were extracted from the studies and presented in tables. When these were not written in the studies, calculations were performed based on data presented in the studies.

Results: Five relevant papers describing two different methods for determining nasogastric tube position were identified: colorimetric capnography (four studies) and capnography (one study).In all four studies examining colorimetric capnography the sensitivity was 100% when nasogastric tubes were inserted intentionally into the airways through an already existing tracheal tube, thereby imitating misplaced nasogastric tubes. When inserted through the nose, the sensitivity was 88-100% and specificity was 99-100%.Capnography obtained a specificity of 100% but sensitivity for when the nasogastric tube was inserted through the nose could not be calculated based on available data.

Conclusions: We found evidence (Level 2b) for colorimetric capnography to be a valid method for verifying nasogastric tube placement.Capnography also detected nasogastric tube position with very high accuracy. However, since these methods were tested in only a single study with a limited sample size, further research is required before clinical recommendations can be made.Despite the impressive results obtained by using colorimetric capnography, implication for practice is not straightforward. A concern is that the colorimetric capnograph is not produced by the manufacture to fit a NG tube and therefore has to be connected to the NG tube by an adaptor-system. Practical issues therefore have to be resolved if the method is supposed to become a standard procedure in a clinical setting.The execution of the procedure using colorimetric capnography differs between the studies. This systematic review therefore recommends that further research should be done to optimize the execution of the procedure.We also recommend that further research be done to reproduce the results obtained using capnography, since this method was tested only in a single study with a limited sample size.