Nasal Highflow (NHF): A New Therapeutic Option for the Treatment of Respiratory Failure

Abstract

The therapy of choice in hypoxemic respiratory failure (type 1) is the application of supplemental oxygen at flow rates of 1 to 15 l/min via nasal prongs or mask. Non-invasive or invasive positive pressure ventilation will be initiated when the oxygen therapy effects are not sufficient or if hypercapnic respiratory failure (type 2) is the underlying problem. Recently, an alternative therapy option is available, from the pathophysiology it can be classified between oxygen therapy and positive pressure ventilation. The therapy called Nasal High Flow (NHF) is based on the nasal application of a heated and humidified air oxygen mixture with a flow range of up to 60 l/min. The precise pathophysiological principles of NHF are only partly understood, yet various aspects are well studied already: it is possible to deliver high oxygen concentrations, airway dryness can be avoided, dead space ventilation reduced and clearance of nasal dead space is achieved. Additionally, an end expiratory positive pressure is built up, which helps to prevent airway collapse, thus resulting in an improvement of respiratory efficiency and reduction of breathing work. Current studies demonstrate improvement in gas exchange and reduction of reintubation rate when applying the NHF treatment in acute respiratory failure. Thus the NHF therapy attracts attention in intensive care medicine. The application in other fields like chronic respiratory insufficiency is less well clarified. The objectives of this review are to present the pathophysiological effects and mechanisms of NHF, as far as understood, and to give an overview over the current state of relevant studies.