BACKGROUND: The randomized controlled trial, TRAUMOX2, compared early restrictive vs. liberal oxygen strategies for trauma patients. The objective of this substudy was to quantify the occurrence and duration of hypoxemic episodes during the trial's eight-hour intervention. METHODS: This observational substudy analyzed a subset of patients at two trial sites in Denmark. Continuous pulse oximetry recorded arterial oxygen saturation (SpO RESULTS: This substudy included 82 patients. After secondary exclusion, 60 patients (median age, 49 years [interquartile range 33-61] and 75% male) were analyzed. Three out of 60 patients (5%) had at least one episode of SpO CONCLUSIONS: In this substudy of 60 patients from the TRAUMOX2 trial, hypoxemia (SpO