Acute Respiratory Distress Syndrome

Clay Wu, DO

Brett Lindgren, DO

Last updated: August 19, 2019

Content

• Definition

• Epidemiology

• Pathophysiology

• Etiologies

• Treatment

Content

• Definition

• Epidemiology

• Pathophysiology

• Etiologies

• Treatment

Mortality rates

27 %

32 %

45 %

All meet chest imaging criteria for ARDS

Content

• Definition

• Epidemiology

• Pathophysiology

• Etiologies

• Treatment

Statistics

• 10% of all patients admitted to the ICU had ARDS

• 23% of mechanically ventilated patients had ARDS

• Increasing mortality with increased severity of ARDS (up to 46%)

Bellani G, Laffey JG, Pham T, et al. JAMA 2016

Content

• Definition

• Epidemiology

• Pathophysiology

• Etiologies

• Treatment

Phases of ARDS

Exudative Proliferative

Fibrotic

Recovery

Hallmark feature is diffuse alveolar damage

Phases of ARDS

• Exudative Phase (First 7 to 10 days)• Pro-inflammatory phase mediated

by alveolar macrophages.

• Leads to damage of the alveolar endothelial and epithelial barriers with accumulation of protein-rich edema fluid within the interstitium and alveolus

Early diffuse alveolar damage

Phases of ARDS

• Proliferative Phase (10-21 days)• Proliferation of Type II

pneumocytes and fibroblasts which aims to restore barrier functions of epithelium, endothelium, and interstitium. Can lead to recovery or fibrotic phase.

Late diffuse alveolar damage

Phases of ARDS

• Fibrotic Phase (> 21 days); Not present in all• Inadequate or delayed re-epithelialization leading to development of

interstitial and intra-alveolar fibrosis.

• Leads to prolonged mechanical ventilation and increased mortality.

Content

• Definition

• Epidemiology

• Pathophysiology

• Etiologies

• Treatment

Etiologies

Direct Lung Injury Indirect Lung Injury

Pneumonia (bacterial, viral, fungal, etc) Sepsis (non-pulmonary source)

Aspiration Transfusion of blood products

Pulmonary contusion Pancreatitis

Inhalational injury Major burn injury

Near drowning Drug overdose

Cardiopulmonary bypass

Content

• Definition

• Epidemiology

• Pathophysiology

• Etiologies

• Treatment

Proven Therapies

Ventilator Basic Principles

• Reduce volutrauma (i.e. low tidal volume, low driving pressure)• Prevent overdistention which may further injure alveolar epithelium

• Permissive hypercapnia

• Goal plateau pressure < 30

• Reduce atelectrauma (i.e. PEEP)• Reduce repetitive opening and closing of alveoli

Lung Protective Strategy (ARDSNet)

• In patients with ARDS, low tidal volume ventilation (initial TV 6ml/kg PBW) had lower mortality and more ventilator-free days.

Brower RG, et al. NEJM. 2000

Prone Positioning (PROSEVA)

• Among patients with moderate-severe ARDS (P:F ratio < 120 mmHg), prone positioning reduces 28-day mortality.

Guerin, Claude, et al. NEJM. 2013

Benefit likely 2/2 more uniform distribution of ventilation and less compression of left lower lobe.

Conservative Fluid Therapy (FACCT)

• A conservative fluid management strategy targeting a CVP <4 mmHg• improves lung function

• decreases ventilator days

• reduces ICU days

• DOES NOT reduce mortality

Wiedemann HP, et al. NEJM. 2006

Debatable Therapies

Debatable therapies

• Neuromuscular blockade

• Steroids (early, never in late (>13 days)

• Pulmonary vasodilators• Inhaled nitric oxide

• Inhaled prostacyclin• Improves oxygenation, but failed to improve mortality

• Veno-venous Extracorporeal membrane oxygenation (VV ECMO)

Neuromuscular Blockade (ACURASYS v. ROSE)

National Heart, Lung, and Blood Institute PETAL Clinical Trials Network. NEJM. 2019

Paralysis with cisatracurium for 48 hours in early severe ARDS improves 90 day survival and increases ventilator-free days.

Papazian L, et al. NEJM. 2010

Paralysis with cisatracurium for 48 hours did not result in a significant difference in 90 day survival compared to lighter sedation targets.

Ineffective therapies

• High-frequency oscillation

• Surfactant replacement

• Neutrophil elastase inhibition

Summary of TreatmentsIn

cre

asin

g in

ten

sity

of

inte

rve

nti

on

300 250 200 150 100 50PaO2/FiO2

Low Tidal Volume Ventilation

Low-Moderate PEEP

Higher PEEP

Mild ARDS Moderate ARDS Severe ARDS

Proven Mortality Benefit

Prone Position

Neuromuscular Blockade

Glucocorticoids (within 14 days of onset)

Inhaled NO

Inhaled prostacyclin

VV ECMO

Rescue Therapies