title: A single intragastric pH electrode does not accurately measure intragastric acidity.
abstract: OBJECTIVE
  Recent studies have raised concerns about the validity of using a single intragastric pH electrode to measure gastric acidity accurately and reproducibly. The aim of this study was to compare simultaneous intragastric pH measurements obtained from an indwelling glass pH electrode to those determined by aspirations from the gastric pool and from ex vivo measurement.
  
  
  METHODS
  Twenty two normal volunteers were studied after fluoroscopically guided placement of a combined nasogastric tube-pH probe assembly. Simultaneous intragastric pH electrode and aspirate pH determinations were made basally for 120 min after administration of 15 ml of antacid (40 mEq buffering capacity) and for another 120 min an hour postprandially after administration of a second 15-ml dose of antacid. Gastric acid concentration (pH) measurements were recorded every 15 min during the following study protocols: 1) fasting baseline (30 min); 2) fasting antacid (120 min); 3) test meal (60 min); and 4) postprandial antacid (120 min).
  
  
  RESULTS
  Intragastric pH was consistently and significantly lower as measured by intragastric pH electrode than by aspiration. Baseline hydrogen ion concentration ([H+]) was 4.3 times higher by direct electrode measurement than by aspirate. Antacid-administered fasting decreased [H+] maximally at 15 min to 48% and 82% of baseline by electrode and aspiration, respectively. The minimal residual intragastric [H+] after fasting antacid was 12.4 times higher by electrode than by aspiration. Postprandial antacid maximally reduced [H+] by 46% at 15 min when recorded using an electrode compared with 60% at 30 min by aspiration. Correlation coefficients for intragastric electrode [H+] versus aspiration [H+] were 0.26 (p = 0.253), 0.61 (p < 0.001), 0.56 (p < 0.01), and 0.31 (p < 0.001), for baseline, fasting antacid, meal, and postprandial antacid, respectively.
  
  
  CONCLUSIONS
  Quantitative evaluations of intragastric acidity (pH) using an intragastric pH electrode and aspiration of gastric juice may yield remarkably different results. Studies that rely on a single intragastric electrode to quantitate intragastric acidity may be highly inaccurate.
authors.affiliation: Department of Medicine, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
authors.forename: R S
authors.initials: RS
authors.lastname: Fisher
authors.forename: D J
authors.initials: DJ
authors.lastname: Sher
authors.forename: D
authors.initials: D
authors.lastname: Donahue
authors.forename: J
authors.initials: J
authors.lastname: Senior
authors.forename: B
authors.initials: B
authors.lastname: Krevsky
mesh_terms: D000328:Adult; D000863:Antacids / Q000494:pharmacology; D002021:Buffers; D002138:Calibration; D004435:Eating; D004566:Electrodes; D005215:Fasting; D005260:Female; D005745:Gastric Acidity Determination / Q000295:instrumentation*; D005898:Glass; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007441:Intubation, Gastrointestinal / Q000295:instrumentation / Q000379:methods; D008297:Male; D012016:Reference Values; D015203:Reproducibility of Results
chemical_list: D000863:Antacids; D002021:Buffers