Ambulatory intraesophageal pH monitoring: the reigning standard for reflux monitoring.

Because of the excellent pioneering work by Doctors Tom DeMeester and Larry Johnson in the 1970s, prolonged pH monitoring became recognized for its great potential to provide quantitative information on gastroesophageal (GE) reflux. Over the ensuing 3 decades, Dr. DeMeester has remained a champion of this technique and his laboratory has provided many of the critical studies to advance it to its present level as the accepted “gold standard” for monitoring acid GE reflux. In this issue of the Journal, Streets and DeMeester provide a comprehensive review of the technique and concepts that have been developed over the years of its evolution, including the development of the reflux score. Originally developed by Johnson and DeMeester in their initial publications, the subsequent revision of the score is now commonly referred to as the “DeMeester Score” and is regularly reported from many esophageal laboratories. This is a thoughtful mathematically derived description of the ambulatory reflux pattern in patients. There are, however, quirks of using this score that should be considered. Anyone performing an interpretation of a pH study must be encouraged to actually look at the actual tracing to ensure that the pH recording has not drifted to a level adjacent to the pH 4.0 cutoff. In those situations where the pH “wiggles” frequently above and below the critical value of 4.0, the computer will analyze each of these as reflux episodes and the score will be dramatically and incorrectly increased. Recent observations by Shay, Johnson, and Richter using other techniques to measure reflux (manometry changes and/or electrical impedance) have shown that acid re-reflux episodes not identified by pH recording frequently occur in patients with abnormal GE reflux patterns. This phenomenon is explained by the slow recovery of the pH electrode after the clearance of the major volume of acid refluxate giving what is usually interpreted as a “false positive” length of acid exposure as demonstrated by Helm et al 1984. These events will be recorded by the standard pH electrode as very long episodes of reflux and the multiple re-reflux episodes will be missed. Thus, acid re-reflex affects every component used in the calculation of the DeMeester score and may provide a very artifactual number. Personally, I find the simple analysis of the actual acid exposure time (time with pH <4) in both the upright and recumbent positions to be the most helpful analysis points from an ambulatory pH study. This information should always be combined with a careful comparison of the relation of reflux episodes to the patient’s symptoms and a symptom index calculated throughout the study. The other area where our personal experience has disagreed with that of Dr. DeMeester and his colleagues relates to the meals ingested during the study. Since the goal of ambulatory monitoring is to evaluate the patient during their usual daily activities, asking them to change their diet dramatically is contradictory to this goal. Having the patient eat the one standardized “hamburger meal” and then avoid any foods with pH below 5 is unrealistic. Foods commonly ingested with a pH less than 5 include coffee, tea, citrus juices, tomato products, wine, and cola beverages. Most people will ingest at least 1 of these with each of their 3 meals during an average day. Confining the patient to a restricted diet is counterproductive to the goal of performing the studies during their “usual daily activities”. Our approach has been to allow the patient to eat their usual meals, particularly those that they know are likely to precipitate their symptoms, and to record the precise beginning and end of the eating period. We then exclude this portion of the tracing from the analysis to avoid potential artifacts produced by acidic meal ingestion. As shown in the accompanying figure, 10 out of 100 consecutive patients from our laboratory having pH monitoring studies had a DeMeester score that changed from normal to abnormal when meals were left in the analysis. This was primarily due to a dramatic increase in number of “reflux” episodes; an artefact produced by acidic foods going down the esophagus.