Ambulatory oesophageal pH monitoring: a comparison between antimony, ISFET, and glass pH electrodes

Ambulatory oesophageal pH-impedance monitoring is a widely used test to evaluate patients with reflux symptoms. Several types of pH electrodes are available: antimony, ion sensitive field effect transistor (ISFET), and glass electrodes. These pH electrodes have not been compared directly, and it is uncertain whether these different types of pH electrodes result in similar outcome.

In an in-vitro model the response time, sensitivity, and drift of an antimony, ISFET, and glass pH electrode were assessed simultaneously after calibration at 22 degrees C and at 37 degrees C. All measurements were performed at 37 degrees C and repeated five times with new catheters of each type. Fifteen patients with reflux symptoms underwent 24-h pH monitoring off PPI therapy using antimony, ISFET, and glass pH electrodes simultaneously.

After calibration at 22 degrees C, pH electrodes had similar response times, sensitivity and drift. In contrast to glass electrodes, antimony electrodes performed less accurately after calibration at 37 degrees C than after calibration at 22 degrees C. Calibration temperature did not affect ISFET electrodes significantly. During in-vivo experiments, significant differences were found in acid exposure times derived from antimony (4.0+/-0.8%), ISFET (5.7+/-1.1%), and glass pH electrodes (9.0+/-1.7%).

In vitro, antimony and glass pH electrodes are affected by different buffer components and temperature, respectively. In vivo, significant higher acid exposure times are obtained with glass electrodes compared with antimony and ISFET pH electrodes. ISFET electrodes produce stable in-vitro measurements and result in the most accurate in-vivo measurements of acid exposure time.