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Learn more: PMC Disclaimer | PMC Copyright Notice BMC Emerg Med . 2026 Mar 5;26:104. doi: 10.1186/s12873-026-01524-9 Search in PMC Search in PubMed View in NLM Catalog Add to search High flow nasal cannula in the emergency department’s resuscitation room: a prospective monocenter descriptive study Juliette Danckaert Juliette Danckaert 1 Department of Emergency Medicine, Nîmes University Hospital, Nîmes, 30900 France Find articles by Juliette Danckaert 1 , Fabien Coisy Fabien Coisy 2 IMAGINE, Department of Emergency Medicine, Montpellier University, Nîmes University Hospital, Nîmes, France Find articles by Fabien Coisy 2, ✉ , Céline Occelli Céline Occelli 3 Medical School, Department of Emergency Medicine, Côte d’Azur University, Nice University Hospital, Nice, France 4 Department of Emergency Medicine, Montpellier University Hospital, Montpellier, France Find articles by Céline Occelli 3, 4 , Sylvain Garnier Sylvain Garnier 5 Medical Intensive Care Unit, Nîmes University Hospital, Nîmes, France Find articles by Sylvain Garnier 5 , Christophe Milesi Christophe Milesi 6 Pediatric Intensive Care Unit, Montpellier University Hospital, Montpellier, France Find articles by Christophe Milesi 6 , Xavier Bobbia Xavier Bobbia 7 IMAGINE, Department of Emergency Medicine, Montpellier University, Montpellier University Hospital, Montpellier, France Find articles by Xavier Bobbia 7 , Romain Genre Grandpierre Romain Genre Grandpierre 1 Department of Emergency Medicine, Nîmes University Hospital, Nîmes, 30900 France Find articles by Romain Genre Grandpierre 1 Author information Article notes Copyright and License information 1 Department of Emergency Medicine, Nîmes University Hospital, Nîmes, 30900 France 2 IMAGINE, Department of Emergency Medicine, Montpellier University, Nîmes University Hospital, Nîmes, France 3 Medical School, Department of Emergency Medicine, Côte d’Azur University, Nice University Hospital, Nice, France 4 Department of Emergency Medicine, Montpellier University Hospital, Montpellier, France 5 Medical Intensive Care Unit, Nîmes University Hospital, Nîmes, France 6 Pediatric Intensive Care Unit, Montpellier University Hospital, Montpellier, France 7 IMAGINE, Department of Emergency Medicine, Montpellier University, Montpellier University Hospital, Montpellier, France ✉ Corresponding author. Received 2025 Sep 23; Accepted 2026 Feb 26; Collection date 2026. © The Author(s) 2026 Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/ . PMC Copyright notice PMCID: PMC13072516 PMID: 41787273 Abstract Background High-flow nasal cannula (HFNC) therapy is commonly used in emergency departments (EDs) to treat acute respiratory failure (ARF). However, its utilization patterns in the resuscitation room (RR) are not well documented. The aim of this study was to describe patient characteristics, management, and in-hospital trajectories according to HFNC use. Methods We conducted a prospective, monocenter, cohort study of consecutive adults admitted to the RR with ARF requiring ≥ 9 L/min of oxygen. We recorded demographic data, comorbidities, clinical and biological parameters, imaging results, treatments, and final ED diagnoses. Patients were classified according to HFNC initiation in the RR. We described clinical pathways through a structured flow diagram that included ICU admission, escalation of respiratory support and in-hospital mortality. Results Among 165 patients, 57 (35%) received HFNC and 108 (65%) did not. Patients receiving HFNC were younger (73 [59; 86] vs. 77 [70;87] years old) and had a lower Charlson index (5 [3; 7] vs. 7 [5; 9]). Median NEWS2 score at admission was 8 [6; 9] in both groups. Infectious pneumonia was the primary ED diagnosis in 84% of HFNC patients (48/57) and 53% of non-HFNC patients (57/108). Cardiogenic pulmonary oedema accounted for 5% (3/57) vs. 21% (23/108), respectively. ICU admission occurred in 39 (68%) of HFNC patients and 40 (37%) of non-HFNC patients. Intubation was performed in 3 (5.3%) vs. 10 (9.3%). In-hospital mortality was 12/57 (21%) in the HFNC group and 35/108 (33%) in the non-HFNC group. Conclusion Patients who receive HFNC therapy in the RR are younger and healthier than those who do not, regardless of the initial severity of acute respiratory failure ARF. The probability of receiving HFNC seems to be linked to the patient’s burden of comorbidities. Further study should explore its impact on patient outcomes. Clinical trial registration None. Supplementary Information The online version contains supplementary material available at 10.1186/s12873-026-01524-9. Keywords: Dyspnea, Emergency department, Resuscitation room, High flow nasal cannula Background Acute respiratory failure (ARF) is defined as a partial pressure of oxygen (pO₂) of less than 60 mmHg for hypoxic ARF (type I), or a partial pressure of carbon dioxide (pCO₂) of greater than 45 mmHg for hypercapnic ARF (type II) [ 1 ]. Respiratory distress is indicated by clinical signs that the respiratory system is unable to maintain proper hemodynamics or decarboxylation. It is a common reason for emergency department (ED) admission [ 2 ]. The main causes of ARF include acute heart failure and decompensation from chronic respiratory disease [ 2 ]. In addition to etiological treatment, the management of hypoxic ARF involves administering oxygen to achieve a pO₂ greater than 60 mmHg. Methods of oxygen delivery include a nasal cannula, a non-rebreather mask, a high-flow nasal cannula (HFNC), non-invasive ventilation (NIV), and orotracheal intubation (OTI) [ 3 ]. Acute respiratory distress syndrome (ARDS) accounts for 1–9% of ED admissions and 7–10% of ICU admissions [ 4 – 5 ]. Epidemiological data on ARF are limited, but its incidence exceeds that of ARDS. HFNC has been validated for treating ARDS [ 6 ], but its use for other conditions is controversial [ 7 – 10 ]. HFNC is increasingly being used in the emergency department (ED) for the treatment of ARF. To our knowledge, few studies have described the ED population receiving HFNC therapy. The primary objective of our study was to describe patients admitted to a tertiary hospital resuscitation room who received HFNC. Secondary objectives included comparing this population with those who did not receive HFNC and describing the in-hospital flow of patients. Methods Legal statement This was a prospective, single-center, observational study conducted at Nîmes University Hospital from December 14, 2022, to December 31, 2023. It was conducted in accordance with reference methodology 004 of the French National Commission on Data Processing and Civil Liberties. The protocol was approved by the local ethics committee (IRB_23.07.02). A note was made in the medical record to confirm that verbal consent was obtained from each participant, and an information letter was provided to each patient or their relative. The study was conducted in accordance with the Declaration of Helsinki. Study population All adults (aged 18 years or older) admitted to the RR for ARF requiring at least 9 L/min of oxygen during their admission were eligible. The threshold of 9 L/min of conventional oxygen therapy was selected to identify patients with substantial oxygen requirements. Although no universally validated cutoff exists, flows above 6–8 L/min are known to approach the performance limits of low-flow devices, resulting in variable delivered fraction of inspired oxygen and insufficient washout of anatomical dead space. In our institution, 9 L/min represents the pragmatic threshold at which HFNC therapy is typically considered for patients with acute respiratory failure. Patients were excluded if they had received prehospital NIV, lacked social security coverage, were pregnant, were minors, or were under legal protection such as guardianship or conservatorship. Objectives The primary objective of our study was to describe the characteristics of patients admitted to the RR for acute respiratory failure ARF who received HFNC. Secondary objectives included comparing this population to those who did not receive HFNC and describing in-hospital patient flow. An exploratory objective was to compare one-hour dyspnea relief among the most severe patients. Data collection Patients admitted to the RR were prospectively enrolled using convenience sampling after obtaining verbal consent. Admission to the RR is for ED patients deemed to be in serious condition or at risk of deterioration, either by the reception nurse or by an emergency physician in charge of the patient. The RR at this hospital has seven beds, with a dedicated physician, intern, nurse, and nursing assistant. The organization of this emergency department has already been described in the literature [ 11 ]. Investigators had access to identifying information for data collection, but this information was not included in the statistical analysis. HFNC initiation was left to the treating physician’s clinical judgment, without predefined criteria, reflecting routine emergency department practice. Data were collected prospectively. Prehospital data were collected from emergency department records. These data included emergency medical service arrival time, vital signs, and ventilation technique used. Information on medical history, smoking status, weight, height, decisions to withhold or withdraw life-sustaining treatment (WLST) according to local procedures [ 12 ], and vital signs at ED admission, RR admission, and RR discharge was collected from emergency medical records. Biological parameters were collected when available, especially arterial blood gas analysis, as well as point-of-care ultrasound, chest imaging, and specific viral polymerase chain reaction testing. The ventilation technique used at discharge from the RR was also recorded. At the start of ventilation and after one hour, the patient was asked to rate their dyspnea on a scale from 0 (no dyspnea) to 10 (extremely severe dyspnea). The difference between these two measurements allowed us to determine the reduction in dyspnea. All data concerning the hospital stay were collected retrospectively within six months of the patients’ RR admission from electronic patient files via individual chart review by a single investigator using a predefined questionnaire. In case of doubt, a second investigator reviewed the chart. For quality assessment, files with abnormal values during statistical analysis were reviewed, and corrections were made if necessary. During hospitalization, information on ventilation methods, length of stay, and discharge arrangements was collected. At the end of hospitalization, the physicians’ final diagnosis was recorded. The Charlson comorbidity index was calculated for each patient after a complete review of the electronic file [ 13 ]. The 30-day survival status of the patients was checked in the French Death Registry ( https://www.deces-en-france.fr/ ). Diagnostic categorization The final diagnoses were grouped into six clinically meaningful categories based on the presumed primary cause of ARF. In accordance with published approaches in epidemiological ARF cohorts [ 5 , 14 ], diagnoses involving pneumonia (viral or bacterial, documented or suspected) were classified as infectious pneumonia, even when associated with other conditions (e.g., acute heart failure or chronic obstructive pulmonary disease [COPD] exacerbation). Diagnoses consistent with aspiration or inhalation were classified as aspiration pneumonia. Exacerbations of COPD or asthma were grouped as COPD/asthma exacerbations. Acute cardiogenic pulmonary edema or decompensated heart failure without evidence of pneumonia were classified as cardiogenic pulmonary edema. Extra-pulmonary infections leading to sepsis were categorized as extra-pulmonary sepsis. All remaining diagnoses, including pneumothorax, pulmonary embolism, malignancy-related respiratory compromise, and miscellaneous conditions, were grouped as “other.” Severity assessment The National Early Warning Score 2 (NEWS-2) was calculated upon admission to the resuscitation room using routinely collected vital signs. Since the level of consciousness was not systematically reported, all patients were assumed to be alert (score 0 on the consciousness component). Patients were classified into low (0–4), medium (5–6), or high (≥ 7) risk categories according to standard thresholds [ 15 , 16 ]. Statistical analysis No imputation technique was used for missing data, which were treated as such. Qualitative variables are presented as absolute numbers and percentages. Quantitative variables are presented as medians with first and third quartiles. Comparisons between qualitative variables were made using the chi-squared test, or Fisher’s exact test when theoretical numbers were less than five. Comparisons between quantitative variables were made using the Mann-Whitney test. A structured patient flow diagram was developed to illustrate post-RR clinical trajectories. After classification according to HFNC initiation in the RR, patients were followed across key outcomes: admission to the ICU, escalation of respiratory support (NIV or OTI), survival, or in-hospital death. Each patient contributed to only one terminal outcome. This approach allows visualization of care pathways and differential prognostic profiles between the HFNC and non-HFNC groups. To visualize the relationship between comorbidity burden and the likelihood of receiving HFNC, a logistic regression model was fitted with HFNC use (yes/no) as the binary outcome and the Charlson comorbidity index as the continuous predictor. We derived predicted probabilities and their 95% confidence intervals from the model and plotted them against the Charlson score to obtain a smoothed probability curve. All statistical tests were two-tailed, with a significance threshold of 0.05. Analyses were performed using R software (version 4.4.0; The R Foundation for Statistical Computing, Vienna, Austria). As this was an exploratory study, no sample size was calculated before inclusions began. Results From December 14, 2022, to December 31, 2023, a total of 5,120 patients were admitted to the RR. Of those patients, 165 (3.2%) were included in the study: 57 (35%) received HFNC therapy, while 108 (65%) did not. The study’s flowchart is presented in Fig. 1 . Figure 2 shows the evolution of ventilation mode during ED care. The cohort consisted of patients with a median age of 76 [67; 86] years, and 79 (48%) were women. Details of the entire cohort are presented in Table 1 . Fig. 1. Open in a new tab Study flowchart. RR: resuscitation room, lpm: liters per minute, HFNC: high flow nasal canula, NRB: non-rebreathing mask Fig. 2. Open in a new tab Point plot presentation of the evolution of ventilation mode, for every patient Table 1. Population’s characteristics No HFNC in RR n = 108 HFNC in RR n = 57 Overall n = 165 p -value Missing Sex: woman, n (%) 55 (51) 24 (42) 79 (48) 0.35 0/0 Age in years, median [Q1;Q3] 77 [70; 87] 73 [59; 86] 76 [67; 86] 0.07 0/0 BMI in Kg.m − 2 , median [Q1;Q3] 25 [22; 31] 25 [21; 28] 25 [21; 30] 0.08 26/6 Admission type , n (%) Ambulances 75 (69) 40 (70) 115 (70) > 0.99 0/0 MICU 26 (24) 10 (18) 36 (22) 0.44 0/0 Spontaneous presentation 7 (6.5) 7 (12) 14 (8.5) 0.24 0/0 Direct resuscitation room admission, n (%) 89 (82) 41 (72) 130 (79) 0.17 0/0 Medical history Charlson comorbidity index , median [Q1;Q3] 7 [5; 9] 5 [3; 7] 6 [4; 8] < 0.01 0/0 Bronchopathy , n (%) 36 (34) 17 (30) 53 (32) 0.75 1/0 Respiratory cancer , n (%) 7 (6.5) 5 (8.8) 12 (7.3) 0.75 0/0 Pulmonary metastasis , n(%) 5 (4.7) 1 (1.8) 6 (3.7) 0.67 1/0 Smoker , n (%) 47 (44) 36 (63) 83 (50) 0.03 0/0 Clinical signs Respiratory distress* , n (%) 81 (75) 37 (65) 118 (72) 0.24 0/0 Auscultatory abnormality , n (%) 88 (82) 50 (88) 138 (84) 0.49 1/0 NEWS 2 at RR admission , median [Q1;Q3] 8 [6; 9] 8 [6; 9] 8 [6; 9] 0.93 39/13 High risk , n (%) 44 (64) 28 (64) 72 (64) > 0.99 - Medium risk , n (%) 19 (28) 8 (18) 27 (24) 0.36 - Low risk , n (%) 6 (8.7) 8 (18) 14 (12) 0.23 - Biological results Hemoglobin in g/dL , median [Q1;Q3] ) 12.9 [11.5; 14.5] 13.0 [11.8; 14.2] 12.8 [11.7; 14.3] 0.95 1/0 Platelets G/L , median [Q1;Q3] 238 [178; 296] 242 [181; 305] 241 [180; 302] 0.78 1/0 White blood cells G/L , median [Q1;Q3] 11.7 [8.4; 15.4] 12.5 [8.1; 16.1] 11.8 [8.2; 15.6] 0.66 1/0 Natremia in mmol/L , median [Q1;Q3] 137 [133; 140] 137 [133; 139] 137 [133; 140] 0.95 1/0 Kalemia in mmol/L , median [Q1;Q3] 4.2 [3.8; 4.5] 4.1 [3.8; 4.5] 4.2 [3.8; 4.6] 0.44 8/0 Albuminemia in g/L , median [Q1;Q3] 37 [34; 40] 36 [33; 40] 36 [33; 40] 0.44 25/10 Creatininemia in µmol/L , median [Q1;Q3] 99 [68; 149] 89 [64; 111] 96 [65; 137] 0.16 2/1 C-reactive protein in mg/L , median [Q1;Q3] 55 [17; 148] 128 [34; 276] 67 [20; 181] < 0.01 3/1 Troponinemia in pg/mL , median [Q1;Q3] 47 [28; 104] 25 [14; 41] 41 [20; 69] < 0.01 46/23 Brain natriuretic peptide in pg/mL , median [Q1;Q3] 3 170 [705; 17 234] 1 218 [502; 4 950] 2 461 [572; 9 809] 0.02 49/30 Lactate in mmol/L , median [Q1;Q3] 1.6 [1.1; 2.8] 1.5 [1.1; 2.4] 1.5 [1.1; 2.7] 0.75 4/0 pH , median [Q1;Q3] 7.39 [7.31; 7.44] 7.43 [7.40; 7.46] 7.41 [7.33; 7.45] < 0.01 4/0 pO2 in mmHg , median [Q1;Q3] 82 [66; 127] 71 [60; 84] 78 [62; 113] < 0.01 4/0 pCO2 in mmHg , median [Q1;Q3] 42 [35; 55] 38 [33; 43] 40 [35; 50] 0.01 4/0 HCO3- in mmol.L-1 , median [Q1;Q3] 26 [23; 29] 25 [22; 29] 26 [23; 29] 0.33 4/0 Care in the emergency room POCUS , n (%) 64 (59) 36 (63) 100 (61) 0.75 0/0 Chest X-Ray , n (%) 29 (27) 14 (25) 43 (26) 0.89 0/0 Chest CT-scanner , n (%) 81 (75) 53 (93) 134 (81) < 0.01 0/0 Viral PCR , n (%) 103 (95) 55 (96) 158 (96) > 0.99 0/0 Antibiotics , n (%) 74 (69) 40 (70) 114 (69) 0.97 0/0 Corticoids , n (%) 17 (16) 12 (21) 29 (18) 0.52 0/0 Aerosols , n (%) 32 (30) 13 (23) 45 (27) 0.49 0/0 Diuretics , n (%) 41 (38) 12 (21) 53 (32) 0.05 0/0 ED Final diagnostic Infectious pneumonia 57 (53) 48 (84) 105 (64) < 0.01 0/0 Cardiogenic pulmonary oedema 23 (21) 3 (5.3) 26 (16) 0.01 0/0 Other 16 (15) 3 (5.3) 19 (12) 0.08 0/0 Extra-pulmonary sepsis 7 (6.5) 2 (3.5) 9 (5.5) 0.72 0/0 COPD/asthma exacerbation 5 (6.5) 1 (1.8) 6 (3.6) 0.67 0/0 Ceiling of care WLST decision in the ED, n (%) 50 (46) 18 (32) 68 (41) 0.10 0/0 No OTI 41 (38) 18 (32) 59 (36) 0.52 - No NIV 19 (18) 2 (3.5) 21 (13) 0.02 - No surgery 23 (21) 4 (7.0) 27 (16) 0.03 - No norepinephrine 33 (31) 13 (23) 46 (28) 0.38 - Open in a new tab COPD: chronic obstructive pulmonary disease, ED: Emergency department, HFNC: high flow nasal canula, MICU: mobile intensive care unit, OTI: orotracheal intubation, POCUS: point of care ultrasonography, RR: resuscitation room, CT: computed tomography, PCR: polymerase chain reaction, WLST: withholding or withdrawing life-sustaining treatment, NEWS 2: national early warning score 2 * Respiratory distress corresponded to a respiratory rate > 25 and use of accessory breathing muscles Patients in the HFNC group were 73 [58; 86] years old, and 24 (42%) were women. The first blood gas analysis revealed a pH of 7.43 [7.40; 7.46], a pO₂ of 71 [60; 84] mmHg, and a pCO₂ of 38 [33; 43] mmHg in the HFNC group. Arterial blood gas values for the overall population are presented in Table 1 . The main ED final diagnosis in the HFNC group was infectious pneumonia ( n = 48, 84%). Figure 3 shows the probability of receiving HFNC according to Charlson’s score. Fig. 3. Open in a new tab Probability of high flow nasal cannula use according to Charlson comorbidity index. HFNC: high flow nasal cannula Patients who received HFNC had a Charlson comorbidity index of 5 [3; 7], while those who did not receive HFNC had a Charlson comorbidity index of 7 [5; 9] ( p < 0.01). The NEWS-2 score at RR admission was 8 [6; 9] in the HFNC group and 8 [6; 9] in the no-HFNC group ( p = 0.93). Supplemental material, Figure S1 A, S1B, and S1C present SpO₂, RR, and mean blood pressure in the prehospital setting, at ED admission, at RR admission, and at RR discharge for patients in the HFNC and no HFNC groups, respectively. Delays between each main step of care are presented in the supplemental material (Table S1 ). Details of the population in the no HFNC group are presented in the supplemental material (Table S2 ). Ventilation modes at RR discharge are presented in the supplemental material (Table S3 ). Figure 4 shows the flow of patients from ventilation mode to diagnostic category and outcomes. Details of patient outcomes are presented in the supplemental material (Table S4 ). Fig. 4. Open in a new tab Flow of patients from ventilation mode to diagnostic category and outcomes. RR: resuscitation room, HFNC: high flow nasal cannula Of the 72 most severe patients (NEWS-2 ≥ 7), 28 (39%) received HFNC, while 44 (61%) did not. Dyspnea numeric scale evaluation data were available for nine (32%) patients in the HFNC group and 16 (36%) patients in the no HFNC group. The median dyspnea numeric scale relief after one hour was − 3 [-4; -2] and − 3 [-4; -2] in the HFNC and no HFNC groups, respectively ( p = 0.64). Discussion In this prospective, monocenter cohort study of patients presenting to the ED RR with ARF requiring ≥ 9 L/min of oxygen, we found that only one-third received HFNC therapy. Patients treated with HFNC were younger and had fewer comorbidities. They were also more likely to be diagnosed with infectious pneumonia. In contrast, patients who did not receive HFNC were more likely to present with cardiogenic pulmonary edema or higher Charlson comorbidity scores. Despite similar initial severity according to NEWS2, the in-hospital trajectories of HFNC patients were markedly different. The clinical profile of patients receiving HFNC is consistent with previously described physiological effects of HFNC, including improved oxygenation, reduced work of breathing, and generation of low-level positive airway pressure [ 17 ]. International recommendations now support the early use of HFNC when high oxygen flows are needed, particularly for hypoxic ARF [ 3 , 6 ]. HFNC is also increasingly incorporated into general ED practice, despite persistent variability in adoption [ 18 , 19 ]. HFNC use was strongly associated with a lower comorbidity burden, as illustrated by the probability curve based on the Charlson index. This finding suggests that ED physicians may preferentially select HFNC for patients perceived as more likely to benefit or with a better physiological reserve. Conversely, patients with high comorbidity scores, particularly those with limitations of care, were less likely to receive HFNC. Several studies have demonstrated that HFNC can alleviate dyspnea, even in palliative patients, but its real-world application in these populations remains inconsistent [ 20 – 21 ]. The predominance of infectious pneumonia among HFNC patients aligns with existing evidence supporting HFNC for hypoxemic ARF of pulmonary origin [ 22 – 24 ]. In contrast, cardiogenic pulmonary edema, a condition for which positive pressure strategies such as NIV are typically preferred, was more prevalent in the non-HFNC group, consistent with previous findings [ 10 ]. Patient flow mapping revealed distinct clinical pathways between groups. Patients who received HFNC were more frequently admitted to the ICU and less frequently intubated. Similar patterns have been reported in previous studies evaluating early HFNC use in selected populations [ 16 , 21 ]. In our cohort, the in-hospital mortality rate (21–33%) was intermediate between that reported in ARF (16–25%) [ 22 ] and ARDS (34–46%) [ 5 ], reflecting the heterogeneity of diagnoses and the broad inclusion criteria. Taken together, these differences in ICU admission and intubation rates are more likely to reflect patient selection, clinical trajectories, and institutional decision-making processes than a treatment effect of HFNC. One-hour dyspnea relief did not differ between NEWS2 ≥ 7 patients with or without HFNC, although dyspnea documentation was incomplete. Previous trials have demonstrated dyspnea reduction attributable to HFNC, but our limited dataset prevents us from drawing firm conclusions. Despite its availability, HFNC was infrequently maintained at resuscitation room discharge, with most patients transitioned to conventional oxygen therapy such as non-rebreather masks. Randomized trials, including HOT-ER, have reported lower rates of escalation in selected patient populations [ 17 ]. In contrast, the real-world ED RR population described in the present study was heterogeneous and unselected, which may partly explain the observed differences in post-ED oxygen strategies. Limited availability of HFNC outside monitored units likely influences discharge decisions from the resuscitation room and may outweigh purely clinical considerations. Limitations Strengths include prospective RR inclusion, granular characterization of diagnostic categories, detailed in-hospital trajectories, and the use of a flow diagram that provides a dynamic view of patient pathways. The population reflects real-world ED practice, with a wide range of ARF etiologies. Our study has several limitations. First, it was conducted in a single center with a relatively small sample size, which may limit generalizability. Second, although all patients were included prospectively, some clinical variables—including dyspnea intensity—were incompletely documented. Third, the inclusion criterion based on an oxygen flow ≥ 9 L/min reflects local practice rather than a validated physiological threshold. In addition, HFNC initiation was left to the treating physician’s clinical judgment in the absence of standardized criteria, which may have contributed to selection bias. Moreover, HFNC settings (flow and oxygen fraction), duration, and timing of initiation were not systematically recorded and therefore could not be analyzed. Fourth, the heterogeneity of underlying causes of acute respiratory failure, similar to what is observed in large epidemiological studies of respiratory distress [ 5 , 14 ], may have introduced clinical variability that could not be fully adjusted for. Finally, although NEWS2 is widely used in EDs and has been validated as a predictor of clinical deterioration [ 15 , 16 ], it remains a punctual assessment and may not fully reflect dynamic changes in severity. Our findings suggest that HFNC is not solely determined by respiratory severity but is also influenced by comorbidity burden and diagnostic category. The association between Charlson score and HFNC initiation warrants further investigation, as it may reflect unconscious clinician bias, perceived futility, or anticipated ward limitations. Future studies should evaluate clinical decision-making processes around HFNC initiation, explore outcomes of patients with WLST who receive or do not receive HFNC, and assess whether systematic HFNC availability in downstream units could modify its use in the ED. Conclusion Patients who receive HFNC therapy in the RR are younger and healthier than those who do not, regardless of the initial severity of acute respiratory failure ARF. The probability of receiving HFNC seems to be linked to the patient’s burden of comorbidities. Further study should explore its impact on patient outcomes. Supplementary Information Below is the link to the electronic supplementary material. Supplementary Material 1 (2.8MB, docx) Acknowledgements None. Abbreviations ARDS Acute respiratory distress syndrome ARF Acute respiratory failure COPD Chronic obstructive pulmonary disease ED Emergency department HFNC High flow nasal cannula ICU Intensive care unit NIV Non-invasive ventilation OTI Oro-tracheal intubation RR Resuscitation room SpO2 Pulse oxygen saturation WLST Withhold or withdraw life-sustaining treatment Author contributions JD: investigation and data curation; FC: formal analysis; JD, FC: conceptualization and methodology; JD, FC, CO: Writing - Original Draft; SG, CM, XB, RGG: Writing – Review & Editing; XB, RGG: supervision and project administration. Funding None. Data availability The datasets generated and analyzed during the current study are not publicly available due to privacy restrictions but are available from the corresponding author on reasonable request. Declarations Ethics approval and consent to participate The local ethics committee of Nimes’ university hospital approved the study (Nîmes University Hospital IRB 23.07.02) and a non-opposition letter was given to patients or their relatives, explaining the aims of the study and the possibility of refusing data collection (Article L1122-1 of the French Public Health Code, as amended by Ordinance No. 2018 − 1125 of 12 December 2018, Article 21). The study was conducted in accordance with the Declaration of Helsinki. Consent for publication Not applicable. Competing interests The authors declare no competing interests. Footnotes Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. References 1. 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