Ambulatory 24-Hour Esophageal pH Monitoring
Jason R. Baker, PhD
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Ambulatory 24-hour esophageal pH monitoring is a study in which continuous esophageal intraluminal pH measurement allows the detection of changes in pH caused by gastroesophageal reflux disease (GERD) episodes. GERD has a prevalence of 8% to 33% impacting all age groups and both genders. Acid reflux episodes are defined as pH drops to below four in the distal esophagus, and reflux time is the elapsed time until the pH exceeds four. Normal subjects do experience reflux episodes primarily after meals, but they are not associated with GERD symptoms. A physiological range of esophageal acid exposure has been established in normal subjects. Prolonged ambulatory 24-hour esophageal pH monitoring enables identification of both symptomatic and asymptomatic reflux events in physiologic conditions.
The value of the test lies in its ability to diagnose GERD in patients with normal endoscopic findings, atypical and extraesophageal symptoms, and poor response to medical, surgical, or endoscopic therapy, as well as in identifying patients who have an increased risk for a complicated outcome (prolonged nocturnal reflux, significant asymptomatic reflux).
Development of thinner pH probes and a wireless pH-sensitive capsule has made the procedure more acceptable to patients, allowing for data collection while patients pursue their everyday activities.
Reflux evaluation may be performed on or off proton-pump inhibitors (PPIs) therapy. To assess acid-exposure time in the esophagus, pH ambulatory monitoring should be performed off PPI therapy in patients without previous markers for GERD. If patients have previous markers for GERD, pH ambulatory monitoring should be performed on PPI therapy to correlate symptomology and refractory symptoms.
Multiple pH sensor probes allow the assessment of high-reflux episodes, involving the proximal esophagus and pharynx, as well as the simultaneous measurement of gastric pH if needed.
Multiple technology is available to place an ambulatory pH catheter. However, a recent study depicted the difference between using high-resolution esophageal manometry data versus the Air Flow Sphincter Locator to determine accurate pH catheter location. The data illustrated that the Air Flow Sphincter Locator was inaccurate over 30% of the time. Thus, using high-resolution esophageal manometry data is recommended to accurately identify the proximal lower esophageal sphincter (LES) border for proper pH catheter placement.
1. Patients with nonerosive reflux disease who are being considered for surgical antireflux repair
2. Patients after antireflux surgery who continue to be symptomatic or are suspected to have ongoing abnormal acid reflux
3. Patients who continue to have GERD-related symptoms despite PPI therapy administered at least twice daily (the test is performed on treatment)
4. Patients with noncardiac chest pain who failed the PPI test or an empirical trial with a PPI administered at least twice daily (the test is performed on treatment)
5. Patients with suspected otolaryngologic manifestations of GERD who failed an empirical trial of PPI therapy administered at least twice daily (the test is performed on treatment)
6. Patients with adult-onset, nonallergic, refractory asthma who failed PPI therapy administered at least twice daily (the test is performed on treatment)
1. Nasoesophageal obstruction or upper esophageal obstruction
2. Severe maxillofacial trauma and/or basilar skull fracture
3. Patients who are unable to cooperate or are high risk for pulling out the pH probe
4. For the wireless pH system, the test is also contraindicated in patients with coagulopathy, severe erosive esophagitis, esophageal ulceration, tight esophageal ring or a stricture, tumor (benign or malignant), varices, any obstruction in the gastrointestinal tract, pacemaker, or implanted cardiac defibrillator
1. Inform the patient of the nature of the examination and that it entails two visits within 24 hours or 48 or 96 hours for the wireless pH system.
2. Discontinue food and liquids 6 hours prior to the study.
3. If the pH study is done off antireflux treatment, confirm that PPIs have been discontinued for at least a week. Prokinetics, H2 blockers, and smooth-muscle relaxants should be stopped for 2 to 3 days prior to the test. Antacids are allowed until a day prior to the test. In contrast, if the test is used to monitor treatment response, the patient should continue all medications.
4. Obtain informed consent.
1. Standard manometry equipment or LES locator (a pressure sensor added to the pH probe)
2. Flexible pH microelectrode with reference electrode or wireless pH capsule (mounted on a delivery device)
3. Dual-sensor catheter that permits assessment of proximal esophageal acid exposure in addition to distal esophageal acid exposure
4. Standard buffer solutions for calibration (pH 7.0 and pH 1.0)
5. Reference electrode (incorporated into the capsule in the wireless pH system)
6. Ambulatory data logger powered by a battery (9 V). For the wireless pH system, an external recorder device receives data signal via radiofrequency telemetry
7. Computer software for data transfer and analysis
8. For the wireless pH system, a custom-made vacuum unit capable of generating 600 mm Hg vacuum pressure to the well in the capsule, via the delivery system
Catheter pH System
1. Calibrate the pH electrode according to the supplier’s instruction manual. If using a dual-sensor pH probe, immerse both sensors in the buffer solution during calibration. Zero the data logger using the software program. Connect the electrode to the data logger, and place it into the 7.0 pH buffer solution for 3 minutes (also place the external reference electrode if you are using a catheter with external reference). The device should read close to 7.0. Rinse the electrode(s) and repeat the procedure with the standard buffer solution at pH 1.0.
2. Locate the LES either by standard manometry (see Chapter 40) or by using LES locator.
3. If utilizing an LES locator, use the LES identification accessory kit. It consists of a pressurized water bag connected through a tubing system to the pH catheter and to a pressure transducer. Adjust the baseline pressure to gastric pressure and withdraw 1 cm at a time. Checking pressure changes with respiration is helpful (increasing below the diaphragm and decreasing above). A sudden rise in resting pressure identifies the LES. After a swallow, there will be a relaxation followed by a pressure wave.
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