combined testing both off and on PPIs, has been suggested to improve the sensitivity of the pH test [55, 62). In GERD patients who failed PPI twice daily, the use of esophageal impedance-pH monitoring is a very promising technique. Multichannel intraluminal impedance monitor- ing with pH sensor (MII-pH) can detect all types of reflux (acidic, weakly acidic, and weakly alkaline). This test measures the resistance of electrical conductivity of the esophageal content, thus detecting any esophageal pH due to the presence of liquid or gas reflux 163, 64]. Moreover, with the inclusions of several channels, it can detect the direction of bolus movement, thus allowing identification of swallows (antero and reflux events (retrograde) 163]. Therefore, it is superior to pH monitoring in the detection of reflux symptoms associated with weakly acidic nonacid reflux in patients on PPI therapy [60