Nasal High Flow to Modulate Dyspnea in Orally Intubated Patients

Rationale: High flow therapy reduces dyspnea in acute respiratory failure but the underlying mechanisms are not fully elucidated. Objectives: To 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). Methods: Dyspnea (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 results: Twenty 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. Conclusions: In orally intubated patients, nasal high flow was associated with lower dyspnea and lower respiratory drive without affecting the inspiratory work.