Treatment of hypoxemic respiratory failure and SARS
Recognition of severe hypoxemic respiratory failure occurs when a patient with respiratory distress has failed standard oxygen therapy, requiring advanced oxygen/ventilation support. If these patients need O2 via a nasal catheter greater than 5 liters/minute to sustain SpO2> 93% and/or have a respiratory rate> 28 ripm or CO2 retention (PaCO2> 50 mmHg and/or pH <7.25) they should be intubated and mechanically ventilated immediately. Thus, mechanical ventilation should be instituted early in patients with persistent hypoxemic respiratory failure (despite oxygen therapy), respecting appropriate precautionary measures [21]. However, the National Health Surveillance Agency (Anvisa), through Technical Note 4/2020, contraindicates the use of non-invasive mechanical ventilation (NIV) and high-flow nasal catheter (HFNC) [6].
The procedure with endotracheal intubation is necessary if the patient does not respond to oxygen therapy. Patients with SARS, especially young children or people who are obese or pregnant, can quickly desaturate during intubation, requiring pre-oxygenation with an inspired fraction of oxygen (FiO2) at 100% for 5 minutes, using a facial mask with reservoir bag. Fast-sequence intubation is appropriate after an airway assessment that shows no signs of difficult intubation [22].
The patient submitted to protective invasive mechanical ventilation may be ventilated in volume or controlled pressure mode (VCV or PCV) with a tidal volume equal to 6 mL/kg of predicted weight and plateau pressure less than 30 cmH2O, with distention pressure or driving pressure (= Plateau pressure minus PEEP) less than 15 cmH2O [7]. It is also necessary to adjust the smallest enough PEEP to maintain SpO2 between 90-95%, with FiO2 <60% (use ARDSNet’s PEEP/FIO2 table for low PEEP (LIGHT SARS). It was found that the use of higher PEEP proved to be causing pulmonary hyperinflation and worsening of the evolution of part of the patients with COVID-19 [7].
In this context, placing patients with SARS in a prone position can improve oxygenation, but patient safety must be guaranteed. In cases of PaO2 / FIO2 less than 150, with adequate PEEP according to the PEEP/FIO2 table, it is suggested to use protective ventilation by placing the patient in a prone position for at least 16 hours. To perform the rotation and to maintain the patient in a prone position, adequate sedoanalgesia should be provided and, if necessary, curarization. The patient can remain supine if, after being ”unresponsive”, he remains with PaO2 / FIO2> 150. Otherwise, one can consider putting the patient back in a prone position [7].
In addition, it is necessary to adopt a conservative fluid management strategy for patients with SARS without tissue hypoperfusion. Prevent the patient from disconnecting from the ventilator, which can result in loss of Peep and atelectasis. It is also necessary to use in-line catheters for suctioning the airways and clamping the endotracheal tube when it is necessary to disconnect (for example, transferring to a transport ventilator or changing the HME filter) [7].