Management of severe acute respiratory distress syndrome: a primer

Abstract

This narrative review explores the physiology and evidence-based management of patients with severe acute respiratory distress syndrome (ARDS) and refractory hypoxemia, with a focus on mechanical ventilation, adjunctive therapies, and veno-venous extracorporeal membrane oxygenation (V-V ECMO). Severe ARDS cases increased dramatically worldwide during the Covid-19 pandemic and carry a high mortality. The mainstay of treatment to improve survival and ventilator-free days is proning, conservative fluid management, and lung protective ventilation. Ventilator settings should be individualized when possible to improve patient-ventilator synchrony and reduce ventilator-induced lung injury (VILI). Positive end-expiratory pressure can be individualized by titrating to best respiratory system compliance, or by using advanced methods, such as electrical impedance tomography or esophageal manometry. Adjustments to mitigate high driving pressure and mechanical power, two possible drivers of VILI, may be further beneficial. In patients with refractory hypoxemia, salvage modes of ventilation such as high frequency oscillatory ventilation and airway pressure release ventilation are additional options that may be appropriate in select patients. Adjunctive therapies also may be applied judiciously, such as recruitment maneuvers, inhaled pulmonary vasodilators, neuromuscular blockers, or glucocorticoids, and may improve oxygenation, but do not clearly reduce mortality. In select, refractory cases, the addition of V-V ECMO improves gas exchange and modestly improves survival by allowing for lung rest. In addition to VILI, patients with severe ARDS are at risk for complications including acute cor pulmonale, physical debility, and neurocognitive deficits. Even among the most severe cases, ARDS is a heterogeneous disease, and future studies are needed to identify ARDS subgroups to individualize therapies and advance care.

Keywords: Acute cor pulmonale; Acute respiratory distress syndrome; Driving pressure; Electrical impedance tomography; Esophageal manometry; Extracorporeal membrane oxygenation; Mechanical power; Positive end expiratory pressure.

Fig. 1

Severe ARDS Treatments. A schematic illustrating management strategies for severe ARDS and refractory hypoxemia. Green sections represent treatments that improve outcomes supported by prospective randomized controlled trials, the orange section represents a treatment that may improve outcomes based on retrospective data, the gray sections represent treatments that may improve oxygenation but have not demonstrated sustained clinical benefit in trials, and the purple sections represent treatments that likely derive benefit in a subset of patients. ARDS acute respiratory distress syndrome, IBW ideal body weight, V_t, tidal volume; and V-V ECMO, veno-venous extracorporeal membrane oxygenation. Adapted from “Risk Factors of Dementia,” by BioRender.com (2023). Retrieved from https://app.biorender.com/biorender-templates

Fig. 2

Advanced methods of PEEP titration. A The stress index, based on the pressure–time curve during constant flow (square-wave) volume-control ventilation. B Electrical impedance tomography with a proposed decremental PEEP titration. The top image depicts global tidal impedance where white indicates the highest volume change, and the bottom image depicts areas of alveolar over-distension (orange) and collapse (white). C Esophageal manometry and associated transpulmonary pressure targets. PEEP_ODCL, PEEP with least over-distended and collapsed lung; P_L, transpulmonary pressure; SI, stress index. Created with BioRender.com

Fig. 3

V-V ECMO considerations. A flowchart illustrating indications for veno-venous ECMO, initial ventilator management, monitoring of right ventricular function and contraindications to ECMO

Fig. 4

V-V ECMO configurations. A schematic illustrating the reconfiguration of conventional V-V ECMO to either right ventricular assist ECMO (OxyRVAD) or veno-arterial venous ECMO (V-AV ECMO). Adapted from “Extracorporeal Membrane Oxygenation (ECMO),” by BioRender.com (2023). Retrieved from https://app.biorender.com/biorender-templates