Nasal High Flow to Modulate Dyspnea in Orally Intubated Patients.

High-flow therapy reduces dyspnea in acute respiratory failure, but the underlying mechanisms are not fully elucidated. To compare dyspnea, we measured airway occlusion pressure (P) and inspiratory work with and without nasal high flow (NHF; Fi, 21%; temperature, 31°C) in intubated patients under pressure support ventilation and during a spontaneous breathing trial (SBT). Dyspnea (determined using numerical rating scale [NRS] and Mechanical Ventilation - Respiratory Distress Observational Scale [MV-RDOS] scores), P, esophageal pressure, respiratory muscle EMG, and arterial blood gas were compared in intubated patients on pressure support ventilation presenting a dyspnea-NRS score higher than 3 during two sequences: ) pressure support ventilation with NHF at 0 L/min followed by 30, 50, and 60 L/min (the last three were randomized) and ) an SBT with NHF at 0 and 50 L/min (randomized). Twenty patients were included. During pressure support ventilation, as compared with a dyspnea-NRS score of 5 (range = 4-6) at an NHF of 0 L/min, dyspnea-NRS scores were 3 (range = 2-6) and 3 (range = 2-5) at NHFs of 30 L/min and 50 L/min, respectively ( < 0.05). However, there was no change in MV-RDOS score, P, esophageal pressure, respiratory muscle EMG, and gas exchange. During the SBT, at an NHF of 50 L/min, dyspnea-NRS score and P were lower than during the SBT at an NHF of 0 L/min ( < 0.01 and  = 0.04, respectively), whereas MV-RDOS score, esophageal pressure, and respiratory muscle EMG did not change as compared with findings in an SBT with an NHF of 0 L/min. In orally intubated patients, NHF was associated with lower dyspnea and lower respiratory drive without affecting the inspiratory work.