Early severe acute respiratory distress syndrome: What's going on? Part II: controlled vs. spontaneous ventilation?

The second part of this overview on early severe ARDS delineates the pros and cons of the following: a) controlled mechanical ventilation (CMV: lowered oxygen consumption and perfect patient-to-ventilator synchrony), to be used during acute cardio-ventilatory distress in order to "buy time" and correct circulatory insufficiency and metabolic defects (acidosis, etc.); b) spontaneous ventilation (SV: improved venous return, lowered intrathoracic pressure, absence of muscle atrophy). Given a stabilized early severe ARDS, as soon as the overall clinical situation improves, spontaneous ventilation will be used with the following stringent conditionalities: upfront circulatory optimization, upright positioning, lowered VO2, lowered acidotic and hypercapnic drives, sedation without ventilatory depression and without lowered muscular tone, as well as high PEEP (titrated on transpulmonary pressure, or as a second best: "trial"-PEEP) with spontaneous ventilation + pressure support (or newer modes of ventilation). As these propositions require evidence-based demonstration, the reader is reminded that the accepted practice remains, in 2016, controlled mechanical ventilation, muscle relaxation and prone position.