Q: How is a 24 hour ambulatory impedance pH test performed?
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A: The procedure was performed by placing an impedance pH probe (ComforTec MII-pH, Sandhill Scientific) that was attached to an ambulatory impedance pH recorder (Sandhill Scientific). The 2.13 mm probe has 8 impedance sensors that are 2 cm apart and 2 antimony pH sensors, 15 cm apart. The probe was calibrated before placement into the oesophagus. The impedance pH probe was advanced via the nares into the oesophagus, after nasal lubrication. The probe was placed such that the distal pH channel was located in the stomach, 10 cm below the lower oesophageal sphincter (LOS) and the proximal pH channel was located in the oesophagus, 5 cm proximal to the LOS. The impedance sensors were located at 2, 4, 6, 8, 10, 12, 14 and 16 cm above the LOS in the oesophagus. The location of the LOS was previously determined by manometry. The patient was encouraged to conduct normal daily activities throughout the study, including consuming usual regular meals, and to record these events using an event button as well as a symptom diary. The patient's antireflux therapy was stopped 1 week prior to the test.
The recordings were carried out for 23 hours 50 minutes and were then downloaded to a computer for graphic display and analysis. The tracing was analysed manually as well as by using the computer software analysis (Sandhill Scientific) for acid reflux and non-acid reflux events and correlation of symptoms with these events.