See also Critical Care: ARDSNET Protocol
Pathophysiology
Scattered, nonhom*ogeneous alveolar damage that leads to oxygenation (V/Q mismatch) problems.
Diagnosis
Berlin definition
- Onset: within one week of a known clinical insult, or new or worsening respiratory symptoms.
- Imaging: bilateral infiltrates on CXR not fully explained by effusions, nodules, or lung collapse.
- Origin: respiratory failure not fully explained by cardiac failure or fluid overload.An objective assessment (e.g., echo) is required to exclude pulmonary edema if no ARDS risk factors are present.
- Oxygenation: (on ventilator settings that include PEEP or CPAP ≥5 cm H20):
- Mild ARDS: PaO2/FiO2 ratio 200-300 mmHg.
- Moderate ARDS: PaO2/FiO2 ratio 100-200 mmHg.
- Severe ARDS: PaO2/FiO2 ratio ≤100 mmHg.
Etiologies
- Direct lung injury: pneumonia, aspiration, pulmonary contusion, fat emboli, near-drowning, inhalational injury, post lung transplantation or hematopoietic stem cell transplant.
- Indirect lung injury: sepsis, severe trauma, shock, drug overdose, DIC, pancreatitis, cardiopulmonary bypass, transfusion of blood products (TRALI).
Management
Mechanical ventilation:
- Goal: maintain adequate gas exchange until the inflammation and edema subside and minimize ventilator-induced lung injury.
- ARDSnet protocol (ARMA Trial): low tidal volume (4-6 mL/kg) and low airway pressure (Pplat ≤30mmHg). See Critical Care: ARDSNet Protocol.
Additional therapeutic considerations:
- “Conservative” fluid management: FACTT trial showed that it improves oxygenation and shortens the duration of mechanical ventilation and intensive care but does not improve 60-day mortality. Goal CVP <4, PCWP <8. Excluded patients with hypotension, pressors, HD, oliguric renal failure.
- Early neuromuscular blockade in severe ARDS: ACURASYS trial (single randomized trial) showed that the use of cisatracurium in patients with severe ARDS resulted in a reduction in 90-day mortality and an increase in ventilator-free days. ROSE trial did not reproduce this mortality benefit.
- Prone positioning: PROSEVA randomized trial showed a reduction in mortality in patients with severe ARDS; recommended for patients with P/F ≤ 100, consider if P/F ≤ 150.
- ECMO and high frequency oscillatory ventilation: further studies are required to evaluate high frequency oscillatory ventilation and extra-corporeal membrane oxygenation. There are no consensus guidelines but consider in P/F ≤ 80.
- Steroids should not be initiated in late ARDS (14 days or longer). The impact of earlier steroid therapy on mortality is uncertain, as the DEXA-ARDS trial showed reduced mortality and improved liberation from the vent but previous studies were less clear.
- Recombinant surfactant does not improve survival or ventilator free days.
- Low-dose nitric oxide temporarily improves oxygenation but not mortality.
Overall care:
- Identify and treat underlying causes.
- Ensure adequate nutrition (preferably enteral).
- Provide GI and DVT prophylaxis.
- Prevent and treat nosocomial infections early.
Adhikari N, Burns KE, Meade MO. Pharmacologic therapies for adults with acute lung injury and acute respiratory distress syndrome. Cochrane Database Syst Rev 2004 4:CD004477.
ARDS Definition Task Force, Acute Respiratory Distress Syndrome: The Berlin Definition. JAMA. 2012;307(23) 2526-33.
ARDSnet. Efficacy and safety of corticosteroids for persistent acute respiratory distress syndrome. N Engl J Med 2006;354:1671-1684.
ARDSnet. Pulmonary-artery versus central venous catheter to guide treatment of acute lung injury. N Engl J Med 2006;354:2213-2224.
Brodie D, Bacchetta M. Extracorporeal Membrane Oxygenation for ARDS in Adults. N Engl J Med 2011; 365:1905-1914.
Comparison of two fluid-management strategies in acute lung injury. The Acute Respiratory Distress Network. N Engl J Med 2006;354:2564-2575.
Diaz JV, Brower R, Calfee CS, Matthay MA. Therapeutic Strategies for Severe Acute Lung Injury. Critical Care Medicine 2010; 38(8) 1644-50.
Fan E, Needham DM, Stewart TE. Ventilatory management of acute lung injury and acute respiratory distress syndrome. JAMA 2005;294:2889-2896.
Fan E, Del Sorbo L, Goligher EC, et al. An Official American Thoracic Society/European Society of Intensive Care Medicine/Society of Critical Care Medicine Clinical Practice Guideline: Mechanical Ventilation in Adult Patients with Acute Respiratory Distress Syndrome [published correction appears in Am J Respir Crit Care Med. 2017 Jun 1;195(11):1540]. Am J Respir Crit Care Med. 2017;195(9):1253‐1263. doi:10.1164/rccm.201703-0548ST
Meduri GU, Golden E, Freire AX et al. Methylprednisolone infusion in early severe ARDS: results of a randomized controlled trial. Chest 2007; 131(4):954.
National Heart, Lung, and Blood Institute PETAL Clinical Trials Network. (2019). Early neuromuscular blockade in the acute respiratory distress syndrome. New England Journal of Medicine, 380(21), 1997-2008.
Papazian L, et al., Neuromuscular blockers in early acute respiratory distress syndrome. NEJM 2010; 363:1107-1116
Piantadosi CA, Schwartz DA. The acute respiratory distress syndrome. Ann Intern Med 2004;141:460-470.
PROSEVA study group. Prone positioning in severe acute respiratory distress syndrome. NEJM 2013: 368(23):2159.
Santacruz JF, Diaz Guzman Zavala E, Arroliga AC. Update in ARDS management: Recent randomized controlled trials that changed our practice. Cleve Clin J Med 2006;73:217-219, 223-225, 229-234.
The Acute Respiratory Distress Syndrome Network. Ventilation with Lower Tidal Volumes as Compared with Traditional Tidal Volumes for Acute Lung Injury and the Acute Respiratory Distress Syndrome. N Engl J Med 2000; 342:1301-1308.
Thompson TB, Chambers RC, Liu KD. Acute Respiratory Distress Syndrome.N Engl J Med 2017; 377:562-572.
Villar J, Ferrando C, Martínez D, et al. Dexamethasone treatment for the acute respiratory distress syndrome: a multicentre, randomised controlled trial. The Lancet Respiratory Medicine. February 2020.
