Reliability of pH measurement and the auscultatory method to confirm the position of a nasogastric tube

Background: Blind placement of a nasogastric feeding tube is a common nursing procedure. Confirmation of the correct position in the stomach is warranted to avoid serious complications such as misplacement in the lung. Testing pH of aspirate from a tube is one of the techniques to confirm the tip position. The purpose of this study was to evaluate the auscultatory method and pH measurement with a pH cut-off point of 5.5 after tube insertion and to compare this with the 'gold standard': an abdominal X-ray. Also the feasibility of the pH method was evaluated.

Materials and methods: Large prospective observational study in a general hospital. In adult hospitalised patients, the positioning of 331 feeding tubes was tested using two different methods to predict tube position in the stomach.

Results: In 98.9% (n=178) of aspirate samples with a pH ≤ 5.5, the tube was located in the stomach. If an aspirate could be obtained, the results of pH measurements showed a sensitivity of 78.4% and a specificity of 85.7%. Obtaining aspirate initially after placement was possible in approximately half of cases but after taking additional measures (including administration of air into the tube, side-positioning of the patient and re-aspiration after one hour) this increased to 81.6%. The sensitivity of the auscultatory method was 79% while the specificity was 61%.

Conclusions: A pH of ≤ 5.5 from tube aspirate is adequate to check the position of the tube in the stomach. Additional measures improve the success to obtain an aspirate from the tube. The auscultatory method is unreliable.