• Valentine Le Stang, Mélodie Graverot, Antoine Kimmoun, Marie-Cécile Niérat, Maxens Decavèle, Thomas Similowski, Alexandre Demoule, and Martin Dres.
• APHP, Sorbonne Université, Hôpital Pitié-Salpêtrière, Service de Médecine Intensive - Réanimation (Département "R3S"), F-75013, Paris, Île-de-France, France.
• Am. J. Respir. Crit. Care Med. 2024 Dec 16.

RationaleHigh flow therapy reduces dyspnea in acute respiratory failure but the underlying mechanisms are not fully elucidated.ObjectivesTo compare dyspnea, airway occlusion pressure (P0.1) and inspiratory work with and without nasal high flow (NHF, FiO2 21%, temperature 31°C) in intubated patients under pressure support ventilation and during a spontaneous breathing trial (SBT).MethodsDyspnea (numerical rating scale, NRS and Mechanical Ventilation - Respiratory Distress Observational Scale, MV-RDOS), P0.1, esophageal pressure, respiratory muscles EMG, arterial blood gas were compared in intubated patients on pressure support ventilation presenting a dyspnea-NRS > 3 during two sequences: 1) pressure support ventilation with NHF at 0 L/min followed by 30, 50 and 60 L/min (the last three were randomized) and 2) a SBT with NHF at 0 and 50 L/min (randomized).Measurements And Main ResultsTwenty patients were included. During pressure support ventilation, as compared to dyspnea-NRS that was 5 (4 - 6) at NHF 0 L/min, dyspnea-NRS was 3 (2 - 6) and 3 (2 - 5) at NHF 30L/min and NHF 50L/min, respectively (p<0.05). However, there was no change in MV-RDOS, P0.1, esophageal pressure, respiratory muscles EMG and gas exchange. During the SBT, at NHF 50 L/min, dyspnea-NRS and P0.1 were lower than during the SBT at NHF 0 L/min (p<0.01 and p=0.04 respectively) whereas MV-RDOS, esophageal pressure, respiratory muscles EMG did not change as compared to SBT with NHF 0 L/min.ConclusionsIn orally intubated patients, nasal high flow was associated with lower dyspnea and lower respiratory drive without affecting the inspiratory work.

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