In the literature there are no indication on which is the best setting of the humidification temperature at the start of treatment with high flow nasal cannula (HFNC) in intensive care unit (ICU). The primary objective of this study is to understand whether there is a difference between the approaches to the humidification temperature for initiating HFNC treatment based on the perceived comfort of ICU patients.

We hypothesize that a gradual increase in temperature (31-34-37°C or 34-37°C) could lead to a different comfort as compared to 37°C as initial starting setting.

The secondary aim is to assess the patient's dryness and humidity level of the nose.

This is a single-center, parallel arm (1:1:1) interventional, non-pharmacological, pragmatic randomized trial. Adult patients who need HFNC treatment for clinical indication will be enrolled and receive a different initial temperature of humidification.

The treatment with HFNC will be carried out as it normally happens for clinical practice, that is the doctor will decide the oxygen concentration, from 21 to 100%, and the flow, from 30 to 60 liters / minute (usually 40-60 liters / minute), according to the patient's level of hypoxia. For the specific purpose of this study, the humidification temperature will be set by the nurse based on the enrollment arm (37°C vs 34-37°C vs 31-34-37°C) rather than by clinical decision. The 37°C arm implies the setting of the temperature immediately at 37°C. The 34-37°C arm implies the setting of the temperature at 34°C and after 15 minutes at 37°C. The 31-34-37°C arm implies setting the temperature initially at 31°C, after 15 minutes at 34°C and after another 15 minutes at 37°C. After 30 minutes at 37°C (target temperature), the patient will be asked to indicate his comfort level, using 5 score visual numerical scale (VNS) ranging from 1 (extreme discomfort) to 5 (best comfort) and the dyspnea level, using Borg scale ranging from 1 (no dyspnea) to 10 (extreme dyspnea). The level of dryness of the nose, HFNC settings and vital signs will also be recorded for each step.

The treatment with HFNC will be provided with the AIRVO 2 (trade mark) system (Fisher & Paykel Healthcare, New Zealand).

All study procedures will be performed at the ICU of the Fondazione IRCCS (Scientific Institute for Research, Hospitalization and Healthcare) Ca' Granda Ospedale Maggiore Policlinico.

Inclusion Criteria:

• Patients need HFNC as per clinical indication
• Patients without ICU delirium (CAM ICU negative)

Exclusion Criteria:

• Patients unable to express informed consent

The principal investigator and the research nurse will be blinded to block size and number. The person responsible for data analysis will be provided an anonymized dataset, thus rendering him/her blinded to the type of treatment the patients received.