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].