Updated: 12/31/2019

Acute Respiratory Distress Syndrome (ARDS)

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Snapshot
  • A 46-year-old woman is admitted to the medical intensive care unit with severe pancreatitis. During the first 72 hours of admission, she becomes confused with increased work of breathing. Her oxygen saturation is 82% and physical exam is remarkable for tachypnea, nasal flaring, and abdominal contractions. She is placed on mechanical ventilation. A chest radiograph demonstrates bilateral infiltrates with no evidence of cardiomegaly or pleural effusions.
Introduction
  • Definition
    • a clinical syndrome characterized by inflammatory lung injury leading to acute hypoxemia and bilateral radiographic infiltrates
      • Berlin Definition of ARDS
        • acute onset (within 1 week of clinical insult or worsening respiratory status)
        • bilateral infiltrates (without an alternative explanation)
        • respiratory failure not caused by cardiac causes or volume overload
        • hypoxemia
      • ARDS severity
        • mild
          • PaO2/FiO2 is 200-300
        • moderate
          • PaO2/FiO2 is 100-200
        • severe
          • PaO2/FiO2 is < 100
  • Etiology
    • pneumonia (most common risk factor)
    • aspiration
    • pulmonary contusion
    • acute pancreatitis
    • sepsis
  • Pathogenesis
    • injury and inflammation to the alveoli increases pulmonary capillary permeability
      • phases 
        • exudative
          • immune-mediated destruction of the epithelial-interstitial-endothelial barrier
            • allows fluid into the interstitium and airspace
        • proliferative
          • recovery of the destroyed barrier
        • fibrotic
          • impaired removal of alveolar collagen that was produced during the early injury process limits functional recovery
    • impaired gas exchange
  • Prognosis
    • severe ARDS has the worst mortality (45%) compared to mild and moderate
Presentation
  • Symptoms
    • dyspnea
  • Physical exam
    • tachypnea
    • tachycardia
    • diffuse crackles
Studies
  • Making the diagnosis
    • based on Berlin definition
Imaging
  • Chest radiography
    • indication
      • initial imaging study in the workup of ARDS
Differential
  • Diffuse alveolar hemorrhage
    • differentiating factor
      • in addition to acute respiratory failure, patients also have an unexplained drop in their hemoglobin concentration
  • Vaping-associated lung disease 
    • ground-glass opacities on imaging that can progress to ARDS
Treatment
  • Approach to treatment
    • the goal is to maintain gas exchange while avoiding ventilator-induced lung injury
  • Interventional
    • mechanical ventilation 
      • indication
        • to maintain adequate gas exchange while minimizing lung injury
          • low tidal volume
          • low plateau pressures
          • titrating up positive end-expiratory pressure (PEEP)
            • PEEP protects against atelectrauma 
      • settings
        • initial tidal volume to 8 mL/kg and reduce gradually to 6 mL/kg (low tidal volumes)  
          • want to achieve an inspiratory plateau airway pressure ≤ 30 cm H2O
        • titrate PEEP to prevent tidal alveolar collapse 
        • initial respiratory rate to approximate baseline minute ventilation (≤ 35/min)
        • oxygenation goal is a PaO2 of 55-80 mmHg
        • pH goal is 7.30-7.45
Complications
  • Nosocomial pneumonia
  • Pneumothorax
  • Chronic respiratory failure
 

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Questions (3)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Volume  
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Urine  
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2
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