Esophageal acid exposure analysis: with or without impedance?

Background: The pH data of multichannel intraluminal impedance-pH testing (MII-pH) may be analyzed by using all pH drops (simulating traditional pH-monitoring) or only analyzing pH drops associated with impedance changes. It is unknown whether the acid exposure measurements would differ between these methods in a group of symptomatic patients. Methods: We evaluated MII-pH studies of patients from 2008 to 2013. Acid analysis was performed in two methods: 1. Creating non-mealtime pH measurements related to retrograde bolus movements (“pH-MII method”) 2. Creating non-mealtime pH measurements anytime the pH fell below 4 (“all-pH method”). Statistical analysis was performed using t-test, Fischer’s test, and logistic regression. Results: 121 patients were eligible. The mean percent total acid exposure time (4.05) was significantly higher in the all-pH method (vs. 1.63 p=0.001). The proportion of patients with abnormal acid exposure time (24.7%) and DeMeester score (24.8%) was higher in the all-pH method (vs. 8.3%, p=0.001; vs. 9.1%, p=0.002). Compared to those without a hiatal hernia (HH), more patients with a HH >2cm had significant differences between analysis methods in upright (19.4% vs. 5.56%, p=0.03), recumbent (29% vs. 6.67%; p=0.002), total time (45.2% vs. 6.67%, p=0.001), and DeMeester score (35.5% vs. 8.89%; p=0.001). Adjusting for age, sex, and PPI usage, HH remained a significant predictor of whether results would differ (OR 12; CI 3.34-42.8 total exposure, OR 8.75; CI 2.36-32.5 DeMeester). Conclusion: Analysis of esophageal acid exposure using all pH data detected more acid reflux than when incorporating impedance measures, particularly in those with a HH. This finding may relate to small volume reflux. Therefore analysis of all-pH reflux rather than just MII-pH should be considered in those patients with a HH.