Adult Respiratory Distress Syndrome

ARDS

Rapidly developing respiratory insufficiency resulting from leakage of protein-rich edema fluid into the alveoli 2° damage to the capillary endothelium

• Synonyms: Shock lung, non-cardiogenic pulmonary edema, post-traumatic pulmonary insufficiency, pump lung, stiff lung syndrome, respirator lung, hemorrhagic lung

• Constellation of Signs and Symptoms

          • Tachypnea, dyspnea, cough

            • Diffuse air-space disease on chest x-ray

            • Severe arterial desaturation resistant to high concentrations of inhaled 0₂

            • Pulmonary function tests showing increased pulmonary vascular pressures and resistances and decreased compliance

• Predisposing conditions:

• Shock

      • Hypovolemic, hemorrhagic

      • Septic-especially gram negative

• Burns

• Massive aspiration of gastric contents (Mendelssohn’s Syndrome)

• Acute pancreatitis

• Heroin/methadone/crack cocaine overdose

• Disseminated intravascular coagulation

• Smoke, chlorine gas, nitrogen dioxide inhalation

• Massive viral pneumonia

• Fat embolism

• Near-drowning

• Pathology

      • Diffuse alveolar damage

            • Damage to type I pneumocytes produces flooding of alveoli with edema fluid

            • Hyaline membranes form and line distal airways and alveoli

            • Type II pneumocytes proliferate to reline denuded alveolar surfaces

            • Fibroblastic tissue is generated in and around airspaces

• X-ray Findings

      • No cardiomegaly

      • No pleural effusions

      • No Kerley B lines

      • Delay in onset of any x-ray findings for at least 12 hours post-insult

      • Between 12 and 24 hours

            • Patchy alveolar infiltrates in both lungs

      • Between 24 and 48 hours

            • Coalesce to produce massive air-space consolidation of both lungs

      • From 5 to 7 days

            • Clearing is frequently 2° effects of CPP ventilation rather than true healing

            • Pneumonia may superimpose

                        • Difficult to recognize but look for new focal infiltrates and pleural effusion

      • More than one week

            • Coarse reticular interstitial disease which may lead to fibrosis

• Complications of CPP ventilation

      • Pneumothorax

      • Pneumomediastinum

      • Pulmonary interstitial emphysema

• Differential Diagnosis

      • Severe bacterial pneumonia--impossible to differentiate except clinically

      • Other forms of pulmonary edema (see below)

WH/94

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