title: Early severe acute respiratory distress syndrome: What's going on? Part I: pathophysiology.
abstract: Severe acute respiratory distress syndrome (ARDS, PaO₂/FiO₂ < 100 on PEEP ≥ 5 cm H₂O) is treated using controlled mechanical ventilation (CMV), recently combined with muscle relaxation for 48 h and prone positioning. While the amplitude of tidal volume appears set < 6 mL kg⁻¹, the level of positive end-expiratory pressure (PEEP) remains controversial. This overview summarizes several salient points, namely: a) ARDS is an oxygenation defect: consolidation/ difuse alveolar damage is reversed by PEEP and/or prone positioning, at least during the early phase of ARDS b) ARDS is a dynamic disease and partially iatrogenic. This implies that the management of the ventilator may be a life-saver by reducing the duration of mechanical ventilation, or detrimental by extending this duration, leading into critical care-acquired diseases. Indeed, a high PEEP (10-24 cm H₂O) appears to be a life-saver in the context of early severe diffuse ARDS; c) tidal volume and plateau pressure cannot be identical for all patients; d) the only remaining rationale for CMV and muscle relaxation is to suppress patient-ventilator asynchrony and to lower VO2, during the acute cardio-ventilatory distress. Therefore, in early severe diffuse ARDS, this review argues for a combination of a high PEEP (preferably titrated on transpulmonary pressure) with spontaneous ventilation + pressure support (or newer modes of ventilation). However, conditionalities are stringent: upfront circulatory optimization, upright positioning, lowered VO₂, lowered acidotic and hypercapnic drives, sedation without ventilatory depression and without lowered muscular tone. As these propositions require evidence-based demonstration, the accepted practice remains, in 2016, controlled mechanical ventilation, muscle relaxation, and prone position.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Petitjeans
authors.forename: Cyrille
authors.initials: C
authors.lastname: Pichot
authors.forename: Marco
authors.initials: M
authors.lastname: Ghignone
authors.affiliation: Physiology, Claude Bernard University, University of Lyon, Lyon, France. lucquintin@yahoo.com.
authors.forename: Luc
authors.initials: L
authors.lastname: Quintin
mesh_terms: D003422:Critical Care; D006801:Humans; D011175:Positive-Pressure Respiration; D012121:Respiration, Artificial; D012128:Respiratory Distress Syndrome / Q000503:physiopathology* / Q000628:therapy
keywords: ARDS; PEEP; Vt; acute hypoxic non-hypercapnic respiratory failure; acute respiratory distress syndrome; contr; driving pressure; low tidal volume; positive end-expiratory pressure; severe ARDS; tidal volume; transpulmonary pressure; ultra-low tidal volume