ARDS

Acute Respiratory Distress Syndrome

Overview• Previously called Adult Respiratory Distress Syndrome• Defined in 1994 American-European Consensus

Conference on ARDS:• Most sever Acute Lung Injury• Diffuse alveolar damage• Severe hypoxemia (PaO2/FIO2 < 200)• Bilateral pulmonary infiltrates• Absence of cardiogenic pulmonary edema (PCWP <18

mmHg)

Epidemiology• 75 cases/ 100,000 population• Can occur at any age• Risks • advanced age• No sex preference• female sex (only in trauma)

• cigarette smoking• alcohol use.

• High APACHE score (any underlying cause)

Pathophysiology

• Diffuse alveolar damage• Increased permeability• Damage to alveolar or capillary endothelium• Inflammation (cytokines, leukotrienes, TNF) • Increased neutrophils ? Reactive

• Severe pulmonary shunting hypoxemia• Pulmonary hypertension

Causative Insults

• Sepsis• Trauma• Fractures • Burns• Massive

transfusion• Pneumonia

• Aspiration• Drug overdose• Near drowning• Cardiopulmonary

bypass• Pancreatitis• Fat embolism

Presentation

• Acute dyspnea and hypoxemia• within hours to days of an inciting event

• Critically ill• Dyspnea, rapidly progressing• Tachypnea• Agitation• Increasing O2 demands• Often multisystem organ failure

Physical Exam• Unspecific• Tachypnea• Tachycardia• Cyanosis• Rales

• Sepsis• Hypotension• Peripheral vasoconstriction

• Manifestation of the underlying cause• i.e abdominal finding pancreatitis

Differential Diagnosis

• Pulmonary hemorrhage• Near drowning• Drug reaction• Noncardiogenic

pulmonary edema• Hamman-Rich

syndrome• Retinoic acid syndrome

• Transfusion-related acute lung injury (TRALI)

• Acute eosinophilic pneumonia

• Reperfusion injury• Leukemic infiltration• Fat embolism syndrome• Acute hypersensitivity

pneumonitis

Workup

• ABG• Hypoxemia• Respiratory alkalosis initially • Respiratory Acidosis ( late)

• BNP- exclude cardiogenic pulmonary edema• CXR diffuse bilateral infiltrates• Echocardiogram • Possible CT

Treatment• Treatment is supportive + underlying cause• No effective drug for prevention nor management• Xigris• Nitric Oxide• Liquid surfactant

• New hopes• Simvastatin • TNF and interleukin antibodies

Treatment• Fluid management• Resuscitation vs. maintenance• Negative fluid balance “dry side of normal”

• Ventilation• Lung protective• High PEEP ( , low TV ( 6 mL/kg)• Neuromuscular block- improved 90 day survival • ECMO- no improved survival• Proning- no improve survival

• Nutrition• Enteral, antioxidants, eicosapentaenoic acid, and gamma-linoleic acid

Prognosis• Mortality • Before 1990 , 40-70%• Recent 30-40%• Better understanding and treatment of sepsis.• Increased in older patients

• Morbidity• VAP• Weight loss/muscle weakness• Only 49% survivors return to work