High Flow Nasal Cannula Versus Non-invasive Ventilation in Prevention of Escalation to Invasive Mechanical Ventilation in Patients With Acute Hypoxemic Respiratory Failure

Oxygen therapy is the first-line treatment in management of acute respiratory failure (ARF). Different oxygen delivery devices have become available over recent decades, either low-flow systems (nasal cannula, simple facemask, non-rebreathing reservoir mask) or high-flow systems (Venturi mask) . The choice of a specific device in management of ARF is based on the severity of hypoxemia, the underlying mechanisms, the patient's breathing pattern and tolerance .

Critically ill patients often require high-flow devices to meet their oxygen needs . Tachypneic patients with ARF, have a peak inspiratory flow rate that is usually high and often exceeds the oxygen flow delivered by the traditional oxygen devices . Using conventional devices, oxygen flow is limited to no more than 15 L/min. Meanwhile, the required inspiratory flow for patients with respiratory failure varies widely in a range from 30 to120 L/min. The difference between patient inspiratory flow and delivered flow is large with conventional oxygen devices leading to patient discomfort . Moreover; high respiratory rate can generate significant entrainment of room air in the mask and dilution of the inspired oxygen with an insufficient oxygen concentration. The suboptimal humidification of the inhaled oxygen provided by standard bubble humidifiers and the limited and unknown inspiratory oxygen fraction (FIO2) delivery are additional drawbacks of these devices .

Since the 90's, noninvasive ventilation (NIV) has been largely used with strong level of evidence in cardiogenic pulmonary edema and chronic obstructive pulmonary disease (COPD) exacerbation. NIV improves gas exchange and reduces inspiratory effort through positive pressure. However, good tolerance to NIV is sometimes difficult to achieve due to frequent leaks around the mask, possibly leading to patient-ventilator asynchrony and even to intubation. It may have other deleterious effects such as delayed intubation by masking signs of respiratory distress, or barotrauma by the high tidal volume potentially generated under positive pressure .

To ensure good results, an appropriate interface is more important than the ventilation mode . Oronasal masks, nasal masks, and hoods are most commonly used for NIV. Oronasal masks are usually tried first because they ensure the effects of NIV better than other interfaces. Unfortunately, it is not comfortable, and many patients find it hard to tolerate. It is also associated with a relatively high incidence of air leakage. Also, skin lesions at the nose induced by long-term use of this device may result in frequent treatment interruptions and discontinuation.

High-flow nasal oxygen therapy (HFNO) is an innovative high-flow system that allows for delivering up to 60 liters/ min of heated and fully humidified gas with a FIO2 ranging between 21% and 100% [.