Impedance monitoring detects a GER episode (MII-GER) if there is a sequential drop in impedance values to less than 50% of the baseline, starting distally and propagating retrogradely to at least the next two more proximal measuring segments (about 4.5 cm above the lower esophageal sphincter (LES)). A GER episode is then defined as acid or non-acid according to its pH: the MII episodes with a pH lower than 4 are defined as acid MII-GERs, whereas the MII episodes with a pH≥4 are defined as non-acid MII-GERs. GERs migration height is the maximum distance from the LES reached by the esophageal refluxate. An acid GER episode is recorded by pH monitoring as a pH drop to less than 4; to be detected by the pH sensor, the pH drop has to last at least 5 s. The total percent time of esophageal exposure to a pH <4 is named Reflux Index (RIpH).