Review article: The measurement of non-acid gastro-oesophageal reflux

BACKGROUND: Oesophageal pH monitoring has been used for three decades to study gastro-oesophageal reflux, but it does not allow detection of non-acid reflux episodes. AIM: To discuss the techniques by which non-acid reflux can be measured and to evaluate the clinical relevance of such measurements. METHODS: Review of the literature on non-acid reflux monitoring. RESULTS: Ambulatory oesophageal impedance monitoring (using a catheter with ring electrodes) allows one to detect all types of gastro-oesophageal reflux, acid as well as non-acid. Measurement of intra-oesophageal bilirubin concentration also detects reflux irrespective of the pH, but only when there is bilirubin in the gastric juice and technical short-comings limit the applicability of this technique. In untreated subjects, about 50% of reflux episodes are non-acid (nadir pH > 4). In patients on acid inhibition, up to 95% of reflux episodes are non-acid. Treatment with an acid inhibitor leads to a significant decrease in the incidence of acid reflux episodes, but not to a reduction in the total number of reflux episodes. This shift is associated with a shift in symptoms from heartburn to regurgitation. With impedance monitoring, the temporal association between symptoms that persist during inhibition of acid secretion and non-acid reflux events can be demonstrated. In a proportion of patients with chronic cough, the coughing episodes are preceded by non-acid reflux. CONCLUSIONS: Intraluminal impedance monitoring of gastro-oesophageal reflux is a feasible technique, which provides clinically important information about the relationships between symptoms and non-acid reflux events