Ambulatory gastric pH monitoring: Proper probe placement and normal values

Abstract

Background: Gastric acid production may persist while patients are treated with proton pump inhibitors. Twenty-four-hour intragastric pH monitoring is being used to identify gastric acid in the stomach while on medical therapy. Aim: To identify the optimal region of the stomach to demonstrate the presence of gastric acid. Method: Probe locations confirmed with fluoroscopy after placement and prior to removal. In experiment 1, five volunteers underwent simultaneous, 24-h gastro-oesophageal pH monitoring with the pH sensors located in the gastric antrum, body, fundus and distal oesophagus. In experiment 2, five volunteers underwent simultaneous 24-h pH monitoring with sensors located side by side in the gastric fundus assessing the reproducibility of gastric pH in this region. In experiment 3, 35 volunteers underwent 24-h pH monitoring with pH sensors located in the distal oesophagus and gastric fundus. The mean percentage time for which pH < 4 was calculated for total, upright, and supine time periods. Results: pH profiles for the gastric fundus and body are similar - the mean percentage total time for which pH < 4 was 92.2% and 90.1%, respectively (P = N.S.). These values are significantly different from the antrum; pH < 4 = 54.6% (P < 0.01). pH values from the gastric fundus are highly reproducible (linear regression P = 0.004, r2 = 0.96). The normal values (mean ± 95th percentile) for percentage time gastric pH < 4 in the fundus were: total 95.6 ± 1.5%, upright 94.8 ± 1.8%, and supine 96.5 ± 2.3%. Conclusion: The fundus is the optimal location to evaluate the presence of gastric acid: pH values are highly reproducible in this area. Normal values for percentage time gastric pH < 4 for a healthy population are now defined.