RESUMO
OBJECTIVE: To compare the performance of combined glass microelectrodes with monocrystalline and polycrystalline antimony electrodes with external reference in a 24-h dynamic in vitro study. DESIGN AND METHODS: In an artificial stomach, the pH of the contents titrated from pH1-7 and back by NaOH and HCI was simultaneously measured at 37 degrees C with antimony and glass probes connected to three recording devices. The recorded data were compared with data monitored continuously by a laboratory pH measurement system. The sensitivity and drift of glass microelectrodes were also analysed in intensive-care unit patients during intragastric pH monitoring for up to 96 h. RESULTS: The sensitivities of antimony polycrystalline, monocrystalline and of glass electrodes were 54.6, 55.3, and 61.8 mV/pH, respectively. The hysteresis was 6.4, 7.2 and 2.75 mV for antimony polycrystalline, monocrystalline and for glass electrodes, respectively. The drift in 24 h was -0.1 pH for glass over the pH range 1-7, and +0.3 pH over pH 1-2.5, and +0.15 pH over pH 2.5-7 for both of the antimony electrodes. The response times of both antimony and glass electrodes were similar over the pH range 2.5-7. The difference in the percentages of time below pH 1.5 was significant: 28.2% for glass, 17.3% for antimony polycrystalline and 18.1% for monocrystalline electrodes, respectively (P < 0.05). However, the difference in the percentages of time below pH 4 was not significant. After 96 h intragastric pH monitoring in six intensive-care unit patients, the mean drift of glass electrodes was 0.15 pH (range, pH 0.1-0.2) and the mean change in sensitivity 1.2%. CONCLUSIONS: (1) Antimony electrodes may be acceptable for intra-oesophageal pH monitoring but are not suitable for intragastric use. (2) The use of glass microelectrodes is recommended for intragastric pH monitoring, particularly when extended monitoring over periods longer than 24 h is required.