Comparison of 4 point-of-care techniques to detect correct positioning of nasogastric tubes in dogs (2020–2021)

Meera Ramesh, Aimee C Brooks, Elizabeth Thomovsky et al.

Background
Accurate placement of nasogastric (NG) tubes in dogs is critical to prevent life-threatening complications such as aspiration pneumonia and pneumothorax. Although radiography is the gold standard for confirming placement, alternative point-of-care (POC) methods such as auscultation, pH measurement, capnography, and ultrasonography are faster and less resource-intensive. This study aimed to compare the sensitivity, specificity, and accuracy of these four techniques against radiography.

Methods
Design: Prospective observational study of 51 hospitalized dogs requiring NG tubes.
POC Techniques:
Air Insufflation with Auscultation: Listening for borborygmus during air bolus administration.
Fluid Aspiration with pH Measurement: Testing gastric fluid aspirates for pH ≤5.
Capnography: Evaluating end-tidal CO2 (ETCO2) waveforms to differentiate between respiratory and gastrointestinal placement.
Ultrasonography: Identifying NG tubes using hyperechoic lines with shadowing in the esophagus or stomach.
Validation: Tube placement was confirmed via two-view thoracic radiography, the reference standard.

Results
1) Placement Accuracy:

-Radiographs confirmed correct placement in 88% (45/51) of cases.
-Misplacement into the respiratory tract occurred in 12% (6/51) of cases.

2) POC Techniques (sensitivity, specificity, and accuracy):

-Auscultation: 84.4%, 50%, 80.4%.
-Fluid Aspiration with pH Measurement: 22.2%, 100%, 31.4%.
-Capnography: 91.1%, 33.3%, 84.3%.
-Ultrasonography: 95.6%, 83.3%, 94.1%.

3) Ultrasonography emerged as the best-performing POC technique overall, with high sensitivity and accuracy but moderate specificity.

4) pH Measurement had perfect specificity but low sensitivity due to frequent inability to aspirate fluid from the tube.

Limitations
-Sample Size: Only six cases involved respiratory misplacement, limiting specificity analysis precision.
-Operator Variability: Differences in training and experience with ultrasonography may influence broader applicability.
-Species Restriction: Findings are limited to dogs and may not generalize to other species.
-Tube Size: Smaller NG tubes reduced capnography performance, influencing accuracy.

Conclusions
Among POC techniques, ultrasonography demonstrated the highest overall performance for detecting NG tube placement in dogs but requires training and experience. Fluid aspiration with pH measurement may complement other techniques due to its high specificity. However, radiography remains the definitive method for confirmation, as no POC technique showed both high sensitivity and perfect specificity.

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