How is fasting gastric pH measurement checked?

Fasting Gastric pH Measurement Procedure

Fasting gastric pH measurement is best performed using a wireless pH capsule placed 6 cm above the squamocolumnar junction during endoscopy, with patients fasting for at least 6 hours prior to the procedure. 1

Patient Preparation

• Patients should fast for at least 6 hours prior to the test to ensure accurate measurement of baseline gastric acidity 2
• If the patient is on acid-suppressing medications:
  • Proton pump inhibitors should be discontinued 7 days before the procedure 2
  • H2 receptor antagonists should be stopped 3 days before the procedure 2
  • Antacids should not be consumed on the day of the study 2
• Informed consent should be obtained, including discussion of potential risks 2

Equipment Options

• Wireless pH monitoring system (preferred method):

  • Consists of a radio telemetry pH capsule attached to a delivery system and external receiver 2
  • Provides more prolonged and comfortable monitoring (48-96 hours) 2
  • Better tolerated than catheter-based systems 2

• Catheter-based pH monitoring:

  • Uses antimony pH electrode(s) 2
  • Can include a second electrode for simultaneous gastric and esophageal pH monitoring 2
  • May include impedance rings to detect retrograde flow of liquid or gas 2

Procedure for Wireless pH Monitoring

1. Preparation:

   • Activate the capsule and check that the wireless receiver is receiving the signal 2
   • Calibrate according to manufacturer's instructions 2
   • Test vacuum suction prior to the procedure 2

2. Placement:

   • Perform endoscopy to determine the location of the squamocolumnar junction 2
   • Insert the wireless capsule via the mouth and place it 6 cm above the endoscopically determined squamocolumnar junction 2
   • Apply suction at a minimum of 550 mm Hg for at least 30 seconds to ensure the esophageal mucosa has filled the suction chamber 2
   • Activate the delivery mechanism to release the capsule 2
   • Confirm capsule attachment by reinserting the endoscope 2

3. Monitoring Period:

   • Monitor for at least 48 hours to increase diagnostic yield 2
   • Can extend monitoring up to 96 hours if results at 48 hours are indeterminate 1
   • Patients should maintain their usual daily activities with minimal restrictions 2

Procedure for Catheter-Based pH Monitoring

1. Preparation:

   • Calibrate the pH probe according to manufacturer's instructions 2
   • Determine the location of the lower esophageal sphincter (LOS) via manometry 2

2. Placement:

   • Insert the probe transnasally 2
   • Position the probe 5 cm above the upper border of the LOS 2
   • For gastric pH measurement, ensure the distal electrode is positioned in the gastric fundus, which provides the most reproducible measurements 3

3. Monitoring Period:

   • Standard monitoring period is 24 hours 2
   • Patients should document timing of meals, symptoms, and supine periods in a diary 2

Important Clinical Considerations

• Wireless pH monitoring is superior to catheter-based monitoring due to:

  • Better patient tolerance 2
  • Less interference with daily activities, eating, and sleeping 2
  • Ability to monitor for longer periods (48-96 hours) 2
  • Accounting for day-to-day variability in acid exposure 2

• The gastric fundus is the optimal location to evaluate gastric acid, as pH values are highly reproducible in this area 3

• Normal values for percentage time gastric pH < 4 in the fundus are:

  • Total: 95.6% (±1.5%)
  • Upright: 94.8% (±1.8%)
  • Supine: 96.5% (±2.3%) 3

Potential Complications and Precautions

• Increased risk of bleeding in patients taking antiplatelet agents or anticoagulants 2
• Early detachment of wireless capsule occurs in 4-15% of cases 2
• Chest pain reported in up to 9% of patients with wireless monitoring, occasionally requiring endoscopic removal 2
• Patients should not undergo MRI examination within 30 days of wireless pH monitoring 2