PH-metry is a diagnostic test used to monitor the pH of the lumen of the stomach and / or esophagus. The excessive acidity of the gastric contents is in fact implicated in the onset of numerous diseases, such as erosions and ulcerations of the mucous membrane of the stomach. An intraluminal environment with a particularly low pH also favors the appearance of esophageal lesions, especially in the presence of close non-physiological refluxes (abnormal ascent of the gastric contents into the esophagus).
The 24-hour esophageal pH-metric is the most sensitive and specific test, and represents the "gold-standard" for the diagnosis of pathological gastroesophageal reflux.
Thanks to pH-metry it is possible to evaluate the degree and time of exposure of the esophagus to reflux, the interval used by the organ to cleanse itself from acid, the relationship of the disorder and its symptoms with meals and the extent of themselves. The pH-metry also allows to establish the most appropriate (pharmacological or surgical) treatment, to then periodically evaluate the effectiveness of the therapy undertaken.
pH-metry: how to do it
The most current version of the exam includes prolonged monitoring, for 24 hours, of endoluminal pH. The pH-metry is performed on an outpatient basis, on a collaborating and fasting patient for at least 12 hours; the presence of food in the stomach would prevent the proper evaluation of reflux and could cause vomiting. For the same reason, in the days preceding the exam it is necessary to suspend the taking of all those drugs capable of affecting the results (sometimes even for 5-10 days); these include antacids, procinecitics, alginates, anticholinergics, muscle relaxants, nitrates, calcium channel blockers, proton pump inhibitors and H2 antagonists.
During the pH-metry, a rubber tube is inserted into the patient's nostril and brought down to the end of the esophagus or in the lumen of the stomach; during the procedure the patient remains seated on a couch and is asked to swallow small sips of water repeatedly in order to favor the descent of the probe. To assess gastroesophageal reflux, this descent will be stopped at about 5 centimeters from the lower esophageal sphincter (intra-esophageal pH-metric), while to investigate the state of health of the stomach it will be continued until reaching the gastric lumen (gastric pH-metry). The examination, substantially, is not painful and at the most causes unpleasant sensations when the tube passes through the throat; for this reason, before proceeding, a small amount of anesthetic is sprayed (xylocaine) in a patient's nostril.
Once the desired anatomical site has been reached, the section of probe that comes out of the nose is fixed with some patches (see figure) and connected to a portable recorder. At the other end of the tube, thanks to the aid of an electrode connected to this end, the pH values are detected, punctually transmitted to the recorder. The next day all the equipment is removed without any pain or discomfort; the data recorded in the 24 hours are then analyzed on the computer and compared with the information recorded by the patient (it is generally requested to report on a specific diary the start and end times of the meal, postural changes, rest breaks and periods of onset of any symptoms). In some cases two minielectrodes are mounted on the tube to capture and record pH fluctuations in two different locations (for example 5 cm above and 5 cm after the lower esophageal sphincter; in this way it is possible to evaluate refluxes not only acidic but also alkaline ).
The examination is contraindicated in the presence of serious cardiovascular or respiratory diseases; all in all, however, it is a safe procedure, which only in a very small part of patients can determine complications related to allergies to the anesthetic (for this it is important to report to the health personnel any allergic episodes from contact with anesthetics). Once the equipment is mounted it is better not to drive and be accompanied to the home by an assistant; during normal daily activities it will be necessary to follow the medical instructions scrupulously, so as not to compromise the outcome of the pH-metry. Among the various provisions, for example, there may be that of eating normally, perhaps avoiding certain foods (very acidic or difficult to digest) without distorting daily habits.
