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24-hour pH monitoring is a test to assess whether acid is coming back into the esophagus from the stomach causing pain, nausea, heartburn, and chest pain. This test involves placing a narrow flexible tube through the nose into the esophagus. Before the test, the nose is numbed with a local anesthetic gel. For the duration of the test, you will keep a diary of any symptoms you experience and record the exact times for when you eat and when you are lying down. Please note, you must return to Endoscopy the next day to remove the tube.