24hr Ambulatory pH Study

Section: UGI Sub-section: Oesophagus

• Gold Standard for diagnosis of GORD
  • Sensitivity and specificity 92%
• Indications:
  • Refractory oesophagitis after PPI tx
  • Atypical presentations
  • Pre-requisite before reflux surgery
• Method
  • Catheter is placed 5cm above the manometrically-determined LES
  • Patient records events & position at time – correlate sx to reflux events
  • Begins ‘reflux episode’ when pH drops below 4, records until above 5](← Gold Standard for diagnosis of GORD
  • Sensitivity and specificity 92%

Normal Values

• < 5% of the time there is acid (pH < 4) in oesophagus
• No. of reflux episodes > 5mins: < 3.5
• No. of reflux episodes pH < 4: 50
• May get false –ves
  • Need to stop PPIs 2/52 before the study
• Generates a DeMeester score
  • Based on SD from the mean of reflux times, length & no of episodes
• Correlation with symptoms important for diagnosis
• NB: Normal 24 hour study but significant symptoms = Likely poor outcome from intervention
• Can add
  • Multichannel intraluminal impedance pH monitoring
  • Bilitec probe (detects bilirubin/bile reflux)

DeMeester Score

• Composite score of acid exposure during a 24hr ambulatory pH study
• Based on six variables
  • Percentage of total time pH < 4
  • Percentage of upright time pH < 4
  • Percentage of supine time pH < 4
  • Number of reflux episodes
  • Number of prolonged reflux episodes >5mins
  • Longest reflux episode
• Normal is < 14.72

Symptom Correlation

• Correlation with symptoms is important for diagnosis
• Multiple calculations to determine symptom to reflux episode association and establish response to PPI.
  • Symptom Index
  • Symptoms severity Index
  • Symptoms Association Probability

Multichannel Intraluminal Impedance pH Monitoring

• Detects changes in impedance
  • Conduction of current across oesophageal wall
  • Will be stable between reflux/swallow
    • Liquids improve conduction and impedance falls
    • Gases reduce conduction and impedance increases
• Most sensitive Ix for GORD
  • Useful for patients with symptoms despite acid suppression
  • 400% more sensitive than pH studies alone
    • High sensitivity – can detect:
      • Swallow or reflux
      • Velocity of transit
      • How long it takes swallow/reflux to be cleared
      • Liquid or gas reflux
      • How proximal reflux extends
      • Degree of pH changes with reflux
• May identify patients who would benefit from fundoplication
  • Despite -ve pH study>)