Clinical vignette A previously healthy 51-year-old woman (height 165 cm, weight 60 kg) was admitted to the ICU with severe community acquired pneumonia. She required intubation and mechanical ventilation 6 h after admission. Her respiratory status declined continuously over the next few hours. Twelve hours after admission, blood gases were as follows: pH = 7.36, PaCO 2 = 47 mmHg, PaO 2 = 65 mmHg, HCO 3 -= 26 mmol/L on FiO 2 = 100 %, Vt set at 340 ml, PEEP at 8 cmH 2 O, respiratory rate at 28/min, and plateau pressure measured at 28 cmH 2 O. She was hemodynamically stable and had a normal renal function.This patient has severe ARDS according to the Berlin definition [1]. This patient has very low respiratory system compliance (18 ml/cmH 2 O) and is ventilated with a high driving pressure (20 cmH 2 O). Hypoxemia is extremely severe with a high oxygenation index (43 cmH 2 O/mmHg). Recent clinical studies showed that hospital mortality in patients experiencing such severe forms of ARDS ranges from 45 to 60 % [1-6].What are the first-line options in this situation?This patient receives only 8 cmH 2 O of PEEP. While higher PEEP confers a survival advantage in severe ARDS patients [7], higher levels of PEEP in this patient very likely will further increase the plateau pressure to levels that are certainly associated with an increased risk of ventilator-induced lung injury. Inhaled nitric oxide might have improved arterial oxygenation although this intervention was not shown to improve long-term survival. On the other hand, prone positioning should be rapidly initiated for more than 16 h since a significant increase in survival [8] has been observed in patients with severe ARDS with this maneuver. This patient should also receive continuous infusion of neuromuscular blockade agents [9].What is the rationale for applying ''ultraprotective'' MV in this situation?Lung hyperinflation occurs in approximately 30 % of ARDS patients ventilated using the protective ARDSNet strategy [10]. Moreover, Hager and co-workers retrospectively analyzing data of the ''ARDSNet'' trial group show a linear relationship between mortality and P plat -a linear relationship in the sense that the lower P plat , the lower the mortality, even for P plat less than 30 cmH 2 O [11]. In a proof of concept study, Terragni et al. [12] demonstrated that very low tidal volume ventilation Intensive Care Med (2015) 41:923-925