gastrointestinal disorders
Ambulatory pH Monitoring
Catheter Based pH Monitoring
A thin tube containing a pH probe is positioned 5 cm above the lower esophageal sphincter. The patient records symptoms, meals, and sleep for 24 hours. Esophageal acid exposure is defined by the percentage of the total recording time that the pH is<4.0. If the time spent with pH < 4.0 is>4.3%, this result is considered abnormal if the patient has not been taking a proton pump inhibitor, and a result > 1.3% is abnormal if the patienthasbeen taking a proton pump inhibitor for the duration of the test. Additional sensors along the more proximal regions of the pH probe allow identification of proximal reflux episodes. A dual-channel esophageal and gastric pH probe has two separate pH sensors along the catheter; one sensor is placed 5 cm above the lower esophageal sphincter, and one sensor is placed in the stomach. The two sensors allow for simultaneous measurement of the pH level in the distal esophagus and in the stomach. This test is most useful for evaluating the efficacy and adequacy of acid-suppressing medications. The newer combined pH-impedance monitoring devices also do multichannel intraluminal Impedance Planimetry , which identifies reflux of any gastric contents into the esophagus regardless of pH level. In addition to acid reflux, this test helps detect weakly acidic reflux (pH between 4.0 and 7) and nonacidic reflux (pH > 7), which would be missed by conventional pH monitoring. The correlation between patient-reported symptoms and reflux events can be assessed using the symptom index or symptom association probability. A significant symptom index value or symptom association probability value suggests that the correlation between symptoms and reflux events is not due to chance. Excessive reflux and significant symptom-reflux correlation are positive predictors of a favorable outcome from antireflux surgery. 