Heated Humidified High Flow Oxygen for Respiratory Support: A Review of Clinical Effectiveness, Cost-Effectiveness, and Guidelines

2019 
Oxygen and/or respiratory support are required for patients in emergency rooms, on the ward and/or in critical care settings during respiratory failure. The most common method to treat this issue, non-invasive ventilation (NIV), is a form of mechanical ventilation that does not require a more invasive endotracheal tube. Most commonly, it inflates the lungs by applying positive pressure to the airway. This can be used in conjunction with or instead of conventional oxygen therapy (COT), including a simple face mask which delivers oxygen.Though commonly used for acute respiratory failure, NIV and COT have limitations. NIV can deliver the same physiologic effects of invasive mechanical ventilation thus preventing the associated risks of intubation including airway trauma, infections and the need for sedation. However, it can be poorly tolerated due to a tight-fitting interface (most commonly oronasal) which is uncomfortable, prone to leakage, and can result in nasal trauma. Further, the benefit over COT has been questioned. COT does not provide a reliable fraction of inspired oxygen (FiO2) or respiratory support, which could increase the need for escalation to more invasive ventilation. Inadequate warming and humidification also make it intolerable for long periods. Dry air can result in dry nose, throat and nasal pain, and reduced mucociliary clearance. Finally, the flow rate of standard oxygen delivery is usually lower ( 120 L/min).Heated, humidified, high flow oxygen is promising because it addresses some of the limitations associated with other oxygen therapies. Oxygen is heated and humidified, and then delivered to the patient usually through nasal cannulae in nasal high flow (NHF) therapy. Up to 100% humidified oxygen can be delivered at a high flow rate (up to 60 L/min) that meets inspiration flow rates, minimizing room air entrainment. The provider sets the flow rate and Fi02. NHF is most commonly used oxygenating patients with severe acute respiratory failure from medical conditions such as pneumonia or bronchiolitis in children. Compared to NIV, NHF decreases anatomical dead space and thus improves alveolar ventilation, though it cannot actively increase inspiratory tidal volume as in NIV. It is also associated with less nasal trauma.Though it is promising and increasingly being used, there are currently no set recommendations for practical application. It is unclear whether greater patient tolerance translates into clinical benefit.
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