The standard of care of patients with ARDS: ventilatory settings and rescue therapies for refractory hypoxemia

Bein, Thomas; Grasso, Salvatore; Moerer, Onnen; Quintel, Michael; Guerin, Claude; Deja, Maria; Brondani, Anita; Mehta, Sangeeta

The second issue is a major clinical challenge in a small, but not negligible, cohort of patients. The first approach to persistent severe hypoxemia should be prone position [38] and neuromuscular blockade [39] . If these do not adequately improve oxygenation, patients are candidates for a "rescue" maximal alveolar recruitment. The simplest, though smart, "open lung approach" is the one proposed by the Express study [33] , which was not exclusively dedicated for "rescue" patients. Briefly, it consists of a stepwise PEEP increase up to an end-inspiratory plateau pressure of 30-32 cmH 2 O (35 cmH 2 O if impaired chest wall elastance is likely), while ventilating with low tidal volumes (V T , i.e., 4-6 ml/kg PBW). LRMs were not mandatory in the Express protocol; however, in "difficult to ventilate" patients they were strongly advised before PEEP titration. Another important approach, though seldom applied in clinical practice, is to optimize the transpulmonary pressure (P L ). Indeed during PEEP and LRMs the driving pressure delivered by the ventilator consists of two components: one to inflate the lung (P L ) and one to expand the chest wall. Simultaneously measuring the airway opening and the esophageal pressure swings generated by positive pressure tidal inflation allows partitioning of the mechanical properties of the lung and chest wall. Accordingly PEEP and LRMs can be titrated safely to an "optimal" P L target. Recent evidence suggests that this could improve "refractory" hypoxemia [40] . The most aggressive open lung approach has been proposed by Barbas et al. [41] and is based on the physiological evidence that alveolar recruitment is a multi-inspiratory phenomenon and the critical "opening pressure" of atelectatic lung units is higher than the pressure needed to keep them open. Barbas et al. [41] proposed to titrate PEEP on the expiratory limb of the respiratory volume-pressure curve (to match the best compliance or the best oxygenation) immediately after a "maximal" LRM. The latter consists of a stepwise PEEP increase up to 45 cmH 2 O, while ventilating the patient with a pressure drive of 10-15 cmH 2