Fig. 3.

Examples of lung ultrasound cumulative patterns of patients presenting with a similar degree of hypoxemia, but very different degree of aeration and respiratory mechanics characteristics, and recalling the recently proposed COVID-19 pneumonia phenotypes [89]. Patient on upper panel presents a nearly normal respiratory system compliance and LUS evidence of a milder lung involvement, reflected in a total LUS score of 11. This suggests a lung condition matching which has been recently described as “Phenotype L,” based on CT findings, and characterized by low lung elastance and low ventilation/perfusion ratio (explaining the severe hypoxia). Based on this imaging and on respiratory mechanics findings, final PEEP was set at 10 cm H₂0. Upper panel shows LUS evidence of a more diffuse and severe diffuse sonographic interstitial syndrome (cause of the shunt and the severe hypoxia), yielding a total LUS score of 27. Respiratory mechanics characteristics recall what has been described as “Phenotype H” (COVID-19 pneumonia: high lung elastance, high right-to-left shunt). Based on this imaging and on respiratory mechanics findings, PEEP was set at 14 cm H₂0 after a stepwise recruiting maneuver. LUS, lung ultrasound