How is a 24 hour ambulatory impedance pH test performed?
The procedure is performed by inserting an impedance pH probe attached to an ambulatory impedance pH recorder. The 2.13 mm probe has 8 impedance sensors that are 2 cm apart and two antimony pH sensors, 15 cm apart. The probe is calibrated before placement into the oesophagus. The impedance pH probe is inserted via the anterior nares into the oesophagus, post nasal lubrication. The probe is placed such that the distal pH channel is located in the stomach, 10 cm below the lower oesophageal sphincter (LOS) and the proximal pH channel is located in the oesophagus, 5 cm proximal to the LOS. The impedance sensors are 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 is 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 is stopped 1 week prior to the test. The recordings are carried out for 23 hours 50 minutes and then downloaded to a PC for graphic display and analysis. The tracing is analysed both manually and digitally with the software for acid reflux and non-acid reflux events and correlation of symptoms with these events.
There is an impedance pH probe projected over the mediastinum. The thicker components of the probe are multiple impedance sensors.
The patient is likely to experience discomfort with a probe placed in their oesophagus for 24 hours and now wireless pH sensor probes are generally employed.