Esophageal and Gastric Diseases Ambulatory 24 - hour Esophageal pH Monitoring

The incidence of gastroesophageal reflux disease (GERD) is increasing and if left untreated can lead to significant patient morbidity and even death. The disease results from the abnormal reflux of gastric contents into the distal esophagus causing symptoms in most and subsequent mucosal damage in some. Several investigations can be used to confirm the diagnosis, but most are dependent on the presence of sequelae and complications of the disease. The physiologic test of ambulatory 24-hour esophageal pH monitoring has proved to be the most sensitive and specific diagnostic investigation. It measures increased esophageal exposure to gastric juice by detecting the concentration of hydrogen ions (pH <4) in the distal esophagus. The technique measures gastric juice exposure at a point 5 cm above the manometrically determined upper border of the lower esophageal sphincter. The exposure is measured in components of frequency of reflux episodes, duration of reflux episodes, and accumulated exposure time. The components are integrated into a composite score, which is reproducible, gender and race independent, and correlates with the degree of esophageal epithelial damage determined histologically. The composite score has been shown to be the most reliable measurement of a therapeutic acid suppression regimen or an effective antireflux operation. It is estimated that up to 11% of the US population experience heartburn daily and 30% every 3 days. Despite such reports the true prevalence of gastroesophageal reflux disease (GERD) within society is difficult to determine because the disease can also cause a variety of atypical symptoms. Further, it is questionable whether individuals who experience heartburn every 3 days have the disease. Consequently, a number of tests are used by the physician to identify individuals who truly have GERD. These include barium swallow, upper gastrointestinal endoscopy, acidperfusion test, and ambulatory 24-hour esophageal pH monitoring. Of these, ambulatory 24-hour esophageal pH monitoring has grown in popularity. This has occurred for 3 reasons: (1) the technique measures and quantifies the basic pathophysiologic problem of GERD, namely the exposure time of the distal esophagus to excessive gastric juice; (2) the measurement is quantitatively related to the degree of esophageal mucosal injury; and (3) the episodes of gastric juice exposure can be correlated with the patient symptoms. This article discusses why ambulatory 24-hour esophageal pH monitoring has become the “gold standard” for the diagnosis of GERD, how to interpret the results using a variety of pH end points, how to perform the study, and the technical modifications that are being made to improve the test. DEFINING GASTROESOPHAGEAL REFLUX DISEASE In clinical practice it is important to have an accurate definition of a condition before setting out to investigate and diagnose it. Unfortunately, over time, the lack of a universally accepted definition for GERD has hindered its investigation and confused the literature. Some investigators have used symptoms to define GERD, while others have concentrated on the presence of its complications, such as endoscopic esophagitis. Defining the pathologic process of gastroesophageal reflux using symptoms or complications is fraught with problems, as will be highlighted in the following section. A more sound definition would consider the pathophysiologic abnormality at play, and thus the definition of GERD adopted by the authors is “the abnormal exposure of the esophagus to gastric juice regardless of symptoms or complications.” In most patients gastric juice contains hydrogen ions that can be used as a marker for the reflux of acid gastric juice into the esophagus. The presence of hydrogen ions are detected by monitoring the esophageal luminal pH over a 24-hour period. WHY ESOPHAGEAL PH MONITORING IS THE GOLD STANDARD FOR THE DIAGNOSIS OF GASTROESOPHAGEAL REFLUX DISEASE The symptoms experienced by individuals considered to have GERD are numerous and varied. Typical symptoms From the Department of Surgery, Keck School of Medicine, University of Southern California, Los Angeles, California. Address correspondence and reprint requests to Dr. Tom R. DeMeester, Chairman of Surgery, Department of Surgery, Keck School of Medicine, University of Southern California, 1510 San Pablo Street, Suite 514, Los Angeles CA. E-mail: [email protected]. J Clin Gastroenterol 2003;37(1):14–22. © 2003 Lippincott Williams & Wilkins, Inc.