Ambulatory gastric pH monitoring: proper probe placement and normal values

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.

To identify the optimal region of the stomach to demonstrate the presence of gastric acid.

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.

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, r(2)=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%.

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.