During COVID-19 pandemic at about 5-6% of patients the heavy anoxemia with need of an intensive care is noted, and some of these patients need invasive or noninvasive ventilation of the lungs. Either heavy pneumonia, or the state similar to ORDS which developed owing to this pneumonia is the reason of hypoxemic respiratory insufficiency. Heavy pneumonia is characterized by fever or suspicion on respiratory infection and a respiration rate more than 30 in a minute, heavy dispnoe or a saturation (SpO2) less than 90% at breath by atmospheric air. The diagnosis of ORDS is made on the basis the clinical managements acting at the moment or the recommendation with the corresponding gradation about severity: ORDS of easy, moderate and heavy degree depending on the relation of partial pressure of oxygen in an arterial blood to fraction of oxygen of the inhaled air. In this article we will consider the possibilities and restrictions of noninvasive ventilation of the lungs (NIVL) at acute respiratory insufficiency.
The reason of heavy respiratory insufficiency at ORDS it is traditionally considered to be disturbance of the ventilating and perfusion relations or the intra pulmonary shunt. Newer data concerning ORDS caused by COVID-19 say that the pathophysiological changes which are the cornerstone of ORDS can be very various. In particular, at these patients not classical ORDS, but so-called atypical ORDS can be observed. Atypical ORDS is characterized by disturbance of mechanisms of perfusion and decrease in hypoxemic vasoconstriction against the background of the kept pulmonary mechanics.
Patients with COVID-19 have dynamics of development of a disease from emergence of the first respiratory symptoms to ORDS and to an intubation can be very fast and take only several days therefore can be required to make the fast decision on carrying out ventilation of the lungs. In the presence the patient of an anoxemia or respiratory insufficiency originally to the forefront has such opportunities of therapy as supply of oxygen through nasal cannulas, or Venturi's mask and a high-line nasal oxygenotherapy. At deterioration in gas exchange and increase in a kislorodozavisimost in dynamics it is necessary to consider existence of indications for CPAP therapy or IVL. Along with definition of indications it is necessary to define not only the IVL form (whether it be invasive or noninvasive ventilation of the lungs), but also timepoint of the transfer to IVL.
NIVL can promote a favorable outcome at its use for patients with classical ORDS only if with its help it is possible to provide protective ventilation of the lungs with the appropriate PEEP high level. At patients with hypoxemic respiratory insufficiency and insufficient efficiency of use of pure oxygen or at the ORDS easy form and also at giperkapnichesky respiratory insufficiency (for example, at an associated disease of heart, HOBL, the hyperventilation caused by obesity, a neuromuscular disease) should make an attempt of treatment with use of NIVL or with use of CPAP therapy at the first stage and then transition to NIVL. At the same time the threshold of an intubation has to be low, and at an aggravation of symptoms (increase in a kislorodozavisimost, sharply or constantly decreasing indicator of a saturation of an arterial blood and/or a respiration rate and strengthening of work of breath), it is necessary to execute immediately an intubation and to begin mechanical IVL. Thus, NIVL can be applied at certain patients at early stages and with an easy form of acute hypoxemic respiratory insufficiency. At the same time more and more data collect that at patients at whom there did not occur improvement at an early stage NIVL only postpones carrying out an intubation, but does not help to avoid it.
Both NIVL, and a high-line nasal oxygenotherapy which is carried out with intervals (depending on the applied settings and at increase in indicators of a stream) is followed by the increased formation of aerosol that in case of COVID-19 results in potential risk of contamination by a virus. Therefore ensuring protection of personnel against an infection should pay special attention. For the same reason it is necessary to define in due time inefficiency of noninvasive IVL, and then it is correct to prepare and carry out the patient's intubation. It allows to avoid the emergency intubation which not only is accompanied by less favorable outcome for the patient, but also owing to increase in time of reaction and insufficient precautionary measures conducts to raised dangers to crew due to increase in virus loading. In view of the same reasons, when carrying out invasive IVL of leak of air it is necessary to minimize. It is necessary to apply mouth-nose and full-front oxygen masks and also helmets to an oxygen therapy and to give preference to devices with a reverse contour. At use of ventilators with an irreversive contour between a mask and the relief valve (or the exhalation valve) it is necessary to install the virus filter.