BackgroundTracheal intubation in the emergency department (ED) can cause serious complications. Available evidence on the use of a high-flow nasal cannula (HFNC) during intubation in the ED is limited. This study evaluated the effect of oxygen therapy by HFNC on oxygen desaturation during tracheal intubation in the ED.MethodsThis was a single-center before-and-after study designed to compare two groups that received oxygen therapy during intubation: one received conventional oxygen, and the other received oxygen therapy using HFNC. We included non-trauma patients who required tracheal intubation in the ED. Linear regression analysis was performed to evaluate the relationship between oxygen therapy using HFNC and the lowest peripheral oxygen saturation (SpO2) during intubation in the conventional and HFNC groups.ResultsThe study population included 87 patients (conventional group, n = 67; HFNC group, n = 20). The median lowest SpO2 in the HFNC group was significantly higher than that in the conventional group (94% [84–99%] vs. 85% [76–91%], p = 0.006). The percentage of cases with oxygen desaturation to < 90% during the intubation procedure in the HFNC group was significantly lower than that in the conventional group (40% vs. 63.8%, p = 0.037). The use of HFNC was significantly associated with the lowest SpO2, and the use of HFNC increased the lowest SpO2 during intubation procedures by 3.658% (p = 0.048).ConclusionWe found that the use of HFNC during tracheal intubation was potentially associated with a higher lowest SpO2 during the procedure in comparison to conventional oxygen administration in non-trauma patients in the ED.