Acute Respiratory Distress (ARD) is defined as the inability of a patient to maintain
normal hematosis. A hematosis disorder is defined as an alteration of the blood gases
with hypoxemia (partial pressure of oxygen (PaO2) less than 80 mm of mercury (mmHg) and
transcutaneous O2 saturation (SpO2) less than 95%), associated or not with hypercapnia
(partial pressure of carbon dioxide (PaCO2) > 45 mmHg) or hypocapnia depending on the
cause of the acute respiratory failure. Compensation mechanisms include increased minute
ventilation, increased ventilatory work and increased cardiac output. When these
compensatory mechanisms are insufficient, acute respiratory distress occurs, along with
signs of heart failure (acute cor pulmonale) and neuropsychic disorders.
Without care, a potentially fatal respiratory decompensation may occur. ARD can be
hypercapnic. It's defined as a PaCO2 greater than 45 mm Hg associated with a drop in
blood pH reflecting respiratory acidosis. Hypoxemic ARD is defined as a PaO2 of less than
60 mm Hg.
A quarter of the patients admitted to the Vital Emergency Room are admitted for severe
hypoxemia resulting from acute respiratory distress.
Like all life-threatening conditions, acute respiratory distress (ARD) requires a rapid
identification and a prompt implementation of effective resuscitation measures.
Oxygen treatment, first described in 1890, remains one of the most important discoveries
in medicine. The purpose of oxygenation is to alleviate respiratory failure and to
restore a satisfactory hematosis. Most experts stress the importance of having an SpO2
target of more than 90% in the majority of patients. While non-invasive ventilation (NIV)
is the standard of care in the initial management of patients with hypercapnic acidosis,
there are currently no recommendations for oxygen therapy in patients with acute hypoxic
respiratory distress in the emergency department.
The choice of the oxygen delivery device is based on the severity of the hypoxemia, the
underlying physiological problems, the type of dyspnea and the patient's tolerance to the
device. The most commonly used devices are nasal cannula, face mask and
high-concentration face mask. They offer several Oxygen Inspired Fraction (fraction of O2
in the gas mixture breathed, FiO2) depending on the oxygen flow rate instituted.
High Flow Nasal Oxygen (HFNO) is used as a complement to conventional oxygen therapy in
emergency departments in general and in particular in the different emergency departments
participating in our study. HFNO is used in hypoxemic respiratory insufficiency according
to the national and international recommendations.
HFNO makes it possible to administer a much higher flow of oxygen than with the usual
hospital and prehospital flow meters. This flow rate can go up to 60-70 L/min with an
FIO2 of 100%. This high flow rate allows to generate low levels of positive pressure in
the upper airways and to adapt the FIO2 delivered up to 100% notably thanks to dedicated
nasal cannulas. HFNO ensures good clinical tolerance and better patient comfort
(humidification and heating of inhaled gases ...) than the other oxygen devices. Its use
was initially developed in paediatric and neonatal intensive care units. It was then
gradually extended to "adult" intensive care units and intensive care units in the
treatment of hypoxemic, non-hypercapnic acute respiratory failure (ARF) with no
indication for orotracheal intubation. The FLORALI study confirms its use as an
alternative to conventional oxygen therapy in intensive care units. Its implementation,
its efficacy (improvement of dyspnea, clinical respiratory signs and oxygenation
parameters), its good tolerance and acceptability by the nursing staff, were recently
demonstrated in an emergency department in 17 patients with hypoxic respiratory
insufficiency. However, despite the increasing number of studies, methodologically
heterogeneous and of insufficient statistical power, carried out on HFNO, these studies
remain non-contributory with regard to the superiority of high nasal flow compared to
conventional oxygen therapy. The gain of the HFNO strategy seems to be established for
clinical ventilatory parameters and dyspnea level. However, the need for therapeutic
escalation and mortality have not been precisely evaluated. On the other hand, there is
very little information on the time required for the implementation of HFNO in the
various studies carried out in patients. The available data indicate that the average
time would usually be more than 90 minutes.
Given the lack of data and clinical trials concerning the systematic use of HFNO in
emergency departments in cases of severe hypoxemia, a prospective study is essential. The
purpose of this work is to evaluate the contribution of early administration of HFNO for
patients with acute non-hypercapnic respiratory distress presenting in the emergency
department, with the aim of obtaining rapid correction of hematosis. The objective of
this work is to compare Conventional Oxygen Therapy (CO) delivered by nasal cannula or
nasal-oral mask at flow rates up to a maximum of 15 liters to HFNO, with the hypothesis
that HFNO would reduce the need for ventilation therapy escalation. The other hypotheses
concern the interest of the HFNO in reducing the use of intensive care hospitalization
and thus the costs of treating these patients.