Heart Rate VAriability as a MaRker for tItrATing hIgh flOw Nasal Cannula Therapy

High-flow nasal cannula is a type of non-invasive respiratory support that helps patients breathe more comfortably. Because the flow is high, it can deliver more oxygen to the lungs and make breathing easier by reducing the effort needed to breathe. However, the best strategy to determine the best oxygen flow rate remains uncertain. Reducing flow rates prematurely can increase work of breathing and prolong ICU stay, while unnecessary prolongation can increase costs. Currently, evidence to guide titration is limited. Heart rate variability is the natural variation in the time between each heartbeat. Heart rate variability reflects the level of autonomic nervous system activity in response to stress. The autonomic nervous system is the part of the nervous system that automatically controls how heart rate speeds up and slows down. When heart rate variability is higher, it indicates that the system is able to adjust to changes in the body, including stress. However, when heart rate variability is low, it indicates that the system is constrained and in a state of stress. The VARIATION study is designed to characterize how heart rate variability goal of this observational study is to learn whether heart rate variability can serve as a marker of the appropriateness of high flow nasal cannula flow support during flow titration in patients with respiratory failure. The main question it aims to answer is: Does heart rate variability change before other conventional respiratory signs when there are changes in respiratory function due to inadequate flow rate? Participants already on high flow nasal cannula as part of their regular medical care will: 1. Undergo a stepwise decrease in high flow nasal cannula flow rate. 2. Be recorded continuously with electrocardiogram and electrical impedance tomography.