Twenty-four hour ambulatory pH monitoring

The most direct method of assessing the relationship between symptoms and GERD is to measure the esophageal exposure to gastric juice with an indwelling pH electrode. Miller first reported prolonged esophageal pH monitoring in 1964, although it was not until 1973 that its clinical applicability and advantages were demonstrated by Johnson and DeMeester. Ambulatory pH testing is considered by many to be the gold standard for the diagnosis of GERD, because it has the highest sensitivity and specificity of all tests currently available. Some experts have suggested that 24-hour pH monitoring be used selectively, limited to patients with atypical symptoms or no endoscopic evidence of GE reflux. Given present-day referral patterns, more than half of the patients referred for antireflux surgery will have no endoscopic evidence of mucosal injury. For these patients, 24-hour pH monitoring provides the only objective measure of the presence of pathologic esophageal acid exposure. Although it is true that most patients with typical symptoms and erosive esophagitis have a positive 24-hour pH result, the study provides other useful information. It quantifies the actual time that the esophageal mucosa is exposed to gastric juice, measures the ability of the esophagus to clear refluxed acid and correlates esophageal acid exposure with the patient's symptoms. It is the only way to quantitatively express the overall degree and pattern of esophageal acid exposure, both of which may impact the decision toward surgery. Patients with nocturnal or bipositional reflux have a higher prevalence of complications and failure of long-term medical control. For these reasons, we continue to advocate its routine use in clinical practice.
The units used to express esophageal exposure to gastric juice are (a) cumulative time the esophageal pH is below a chosen threshold, expressed as the percent of the total, upright, and supine monitored time; (b) frequency of reflux episodes below a chosen threshold, expressed as number of episodes per 24 hours; and (c) duration of the episodes, expressed as the number of episodes greater than 5 minutes per 24 hours and the time in minutes of the longest episode recorded. The upper limits of normal were established at the 95th percentile. Most centers use pH 4 as the threshold. Combining the result of the six components into one expression that reflects the overall esophageal acid exposure below a pH threshold, a pH score was calculated by using the standard deviation of the mean of each of the six components measured.