OBJECTIVE Gastric ulcer and hemorrhage are major complications in patients with chronic respiratory failure, but upper GI endoscopy tends to be avoided because of possible cardiopulmonary events. This study was designed to evaluate hypoxemia and subsequent cardiac complications during gastroscopic procedures in patients with chronic respiratory failure undergoing long-term home oxygen therapy (LHOT). METHODS Gastroscopy was carried out in 10 patients undergoing LHOT and 10 age-matched control subjects without pulmonary diseases. Oxygen saturation and cardiac arrhythmias before and during gastroscopy were monitored. Patients were given 10 mg intramuscular scopolamine butylbromide and local anesthesia using 100-300 mg lidocaine gel 15 minutes before the procedure. Each patient continued to receive oxygen via a nasal cannula in the same dosage as their daily use. RESULTS Decrease in oxygen saturation during endoscopic procedure was significantly greater in patients undergoing LHOT (from 95.9+/-0.9 to 93.4+/-1.7%) compared with control subjects (from 96.7+/-0.4 to 96.2+/-0.4%). There was a significant correlation between the degree of hypoxemia and the oxygen dosage required for their daily treatment in the patients (r = 0.727, P<0.02). CONCLUSIONS These results indicate that the degree of respiratory failure influences the degree of decrease in oxygen saturation during gastroscopy. It is suggested that use of the nasal route for oxygen supply may be one of the major causes of the hypoxemia.