Background  The monitoring of gastric pH value is of great significance in preventing stress ulcers, evaluating the efficacy of antacid therapy and predicting the position of nasogastric tube. However, the commonly used tools for monitoring gastric pH value have certain limitations. The new gastric tube that can monitor the pH value (hereinafter referred to as the new gastric tube) is the latest monitoring tool developed by our research group, which can realize the functions of pH monitoring and nasal feeding/gastrointestinal decompression at the same time.

  Objective  To evaluate the reliability of the new gastric tube in measuring the pH value of gastric juice in vitro.

  Methods  A total of 214 gastric juice samples were collected from 51 patients with indwelling gastric tubes in the Hepatobiliary Surgery and General Surgery Wards of the First Medical Center of Chinese PLA General Hospital from September to October in 2022. Gastric juice samples were measured using a new gastric tube and a laboratory pH meter, respectively. Taking the pH value measured by the laboratory pH meter as the benchmark, the gastric juice samples were divided into three groups with pH≤4, 4<pH<7 and pH≥7. The reliability of the new gastric tube was evaluated by paired t-test, equivalence/non-inferiority test results of measurement data, Pearson correlation analysis and Bland-Altman consistency test.

  Results  Difference test: According to different pH value intervals, the difference between the pH value of the gastric juice measured by the new gastric tube and the laboratory pH meter was compared (paired t test), and the results showed that there was no statistically significant difference in the pH value of each interval (P>> 0.05). Equivalence/non-inferiority test results: Taking the equivalence boundary value as 0.1 (pH≤4 interval) or 0.2 (other intervals or the entire interval), after one-sided test, the new gastric tube test results (pH value) were not inferior or equivalent to laboratory pH meter test results (P<0.025). Pearson correlation coefficients of pH values ​​measured by the two tools in different groups were 0.901, 0.851, 0.564, (P<0.001). In each group, 4.76% (2/42), 2% (2/100), and 2.78% (2/72) of the two tools were outside the limit of agreement (LoAs) of the 95% CI. The upper and lower limits of the 95% CI of the LoAs of the difference in values were within the clinically acceptable range.

  Conclusion  The pH value of the gastric juice measured by the new gastric tube is consistent with that measured by the laboratory pH meter, especially in an acidic environment. It is preliminarily believed that the new gastric tube developed by our research group that can monitor the pH value has high accuracy and reliability in measuring the pH value of gastric juice. In the next step, we will conduct further in vitro and in vivo verification after debugging the gastric tube, so as to better serve the clinic.