The aim of this study was to determine the role that heated, humidified high-flow nasal oxygen (HHHFNO) plays in the adult ED with particular focus on the indications and outcomes of use. An explorative study was undertaken using retrospective chart review to identify characteristics of adult patients who received HHHFNO in a tertiary adult ED between January and December 2014. Thirty-nine patients were identified as having received HHHFNO during the study period with a range of indications for this use. No clear guidelines existed for initiation of this use. Two patients failed on HHHFNO therapy, requiring increased respiratory support; twenty-seven patients were admitted to hospital with HHHFNO still being delivered and seven patients were successfully treated with HHHFNO in the ED. The use of HHHFNO was associated with a 4.91bpm (95% CI 2.23-7.59; P=0.001) decrease in mean RR and an 11.26bpm (95% CI 4.62-17.90; P=0.002) decrease in mean HR from baseline at 120min of use. Hypercapnic patients showed a significant decrease in mean PaCO2 levels after one hour of HHHFNO use (70.33mmHg (SD 19.63) vs. 55.00mmHg (SD 13.28), P=0.041) with no change in PaCO2 levels in patients who were not hypercapnic prior to HHHFNO use (PaCO2 32.71mmHg (SD 5.28) vs. 32.38mmHg (SD 3.70), P=0.919). HHHFNO is currently being used as a device for supplemental oxygen delivery within the adult Emergency Department; however, further research is needed in this area to quantify its use in many of the indications seen.