Detection of duodenal fluid in the oesophagus with a sodium ion selective electrode *

The assessment of duodeno‐oesophageal reflux is difficult as, until recently, no technique has been readily available for continuous ambulatory monitoring. A sodium ion selective electrode placed in the stomach has been previously shown to detect duodenogastric reflux by using sodium as a marker. This relies on the difference in sodium concentration between gastric (5–60 mmol/L) and duodenal, biliary and pancreatic (150 mmol/L) fluids. In this pilot study to assess the efficacy of the electrode in the distal oesophagus, eight subjects without symptomatic gastro‐oesophageal reflux and eight subjects with known duodenogastric reflux were studied. Thirty millilitre volumes of varying sodium solutions (40, 80, 100 and 140 mmol/L) were swallowed to assess the response of the electrode to sodium ions. In both groups, this revealed a constant and reproducible rise in response with increasing concentration ( P < 0.0001). The stomachs of subjects with duodenogastric reflux were aspirated via a nasogastric tube to obtain 12 different samples of gastric fluid. This was assayed for sodium and bile acid concentration. The fluid was then reinfused as a 30 mL bolus into the oesophagus through a tube to simulate oesophageal reflux. A rise equivalent to 40–72 mmol/L Na + was recorded by the electrode in response to samples that contained 58–81 mmol/L Na + and 0.4–16 mmol/L bile acids, recorded by quantitative analysis, and a response of up to 20 mmol/L Na + was recorded by the electrode to sodium concentrations < 49 mmol/L and bile acid concentrations of 0.005–0.6 mmol/L. The response was appropriate to the assayed bile acid concentration in all but one sample. The sodium ion selective electrode responds to bile containing fluids introduced into the oesophagus. Further investigation is warranted to determine its ability to measure duodeno‐oesophageal reflux continuously.