Severe COVID-19
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Factors and characteristics to develop one type over the other have been identified: severity of the initial infection, the patient’s immune response, the patient’s physical fitness and comorbidities, the response of the hypoxemia to the ventilation, and the time between first symptoms and hospital admission (Gattinoni 2020). L type patients remain stable before improvement or deterioration. In the latter case the patients develop H type pneumonia (Pfeifer 2020). According to this theory, a ventilation strategy starting with respiratory support with high flow oxygen has been recommended (Gattinoni 2020). To adequately assess oxygenation, the oxygen content (CaO2) in the blood is helpul, as it describes the actual oxygen supply (DO2) better than the oxygen partial pressure (pO2), particularly when combined with the cardiac output (CO): DO2 = CaO2 x CO and CaO2 = Hb x SaO2 x 1.4 With a CaO2 limit of 10 g/100 ml blood, and an appropriate cardiac output, i.e., absence of cardiac failure, a lower O2 saturation (hypoxemia) can be tolerated in the blood before a critical oxygen shortage in the tissue (hypoxia) develops. Therefore, rather than strictly focusing on pO2 values as represented by the oxygenation index PaO2/FiO2 of < 150, it is more reasonable to consider the overall clinical picture while setting individual target values before intubation. Attempting high-flow oxygen and non-invasive ventilation in patients with type L pneumonia is recommended. Intubation should only be performed if there is significant clinical deterioration (Lyons 2020, Pfeifer 2020).
Special situations in severe COVID-19 Prone positioning Prone position (PP) has become a therapeutic option, even in awake, nonintubated patients, during spontaneous and assisted breathing (Telias 2020). In one study, among 50 patients, the median SpO2 at triage was 80%. After supplemental oxygen was given to patients on room air it was 84%. After 5 minutes of proning was added, SpO2 improved to 94% (Caputo 2020). Whether PP prevents intubation is not known yet. In a prospective before-after study in Aix-en-Provence, France among 24 awake, non-intubated, spontaneously breathing patients with COVID-19 and hypoxemic acute respiratory failure requiring oxygen supplementation, the effect of PP was only moderate. 63% were able to tolerate PP for more than 3 hours. Oxygenation increased in only 25% and was not sustained in half of
COVID Reference ENG 006.9
