A 22-year-old woman was admitted to hospital for investigation of persistent nausea, vomiting and weight loss of 7 kg. She had undergone an appendectomy two months earlier but was otherwise healthy and was only taking antiemetics. An endoscopy performed one month earlier in a local hospital revealed gastritis and duodenitis. The day after admission she developed coffee ground hematemesis and a repeat gastroscopy was performed. Before the endoscopy, the patient received topical Hurricane spray to the oropharynx. The patient was sedated with 6 mg of midazolam and 100 pg fentanyl in incremental doses. The gastroscope was introduced into the esophagus without difficulty. A shallow, clean-based gastric ulcer was found in the antrum but the endoscopy was otherwise unremarkable. During the procedure, the O2 saturation was noted to be 88%. O2 was administered at a rate of 4 L/min by nasal prongs. She was transferred to the inpatient ward in stable condition; however, her O2 saturation remained in the 85% to 88% range. O2 was administered with a nonrebreathing mask but her O2 saturation remained lower than 88%. She was alert and oriented, and complained of mild dyspnea. Her chest exam was normal and her chest x-ray was also unremarkable.