Nasal High Flow to Modulate Dyspnea in Orally Intubated Patients

Abstract

Rationale: High-flow therapy reduces dyspnea in acute respiratory failure, but the underlying mechanisms are not fully elucidated. Objectives: To compare dyspnea, we measured airway occlusion pressure (P_0.1) and inspiratory work with and without nasal high flow (NHF; Fi_O2, 21%; temperature, 31°C) in intubated patients under pressure support ventilation and during a spontaneous breathing trial (SBT). Methods: Dyspnea (determined using numerical rating scale [NRS] and Mechanical Ventilation - Respiratory Distress Observational Scale [MV-RDOS] scores), P_0.1, 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: 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) an SBT with NHF at 0 and 50 L/min (randomized). Measurements and Main Results: 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 (P < 0.05). However, there was no change in MV-RDOS score, P_0.1, esophageal pressure, respiratory muscle EMG, and gas exchange. During the SBT, at an NHF of 50 L/min, dyspnea-NRS score and P_0.1 were lower than during the SBT at an NHF of 0 L/min (P < 0.01 and P = 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. Conclusions: In orally intubated patients, NHF was associated with lower dyspnea and lower respiratory drive without affecting the inspiratory work.

Keywords: dyspnea; high-flow nasal cannula; high-flow nasal oxygen; nasal breathing; respiratory drive.