Cancer of the Lung by liaoqinmei

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									Acute Respiratory Distress
       Syndrome
          Module G5
    Chapter 27 (pp. 369-378)
               Compliance
• Compliance = D Volume
                D Pressure
• Normal Values
  • Lung 0.2 L/cm H20
  • Thorax 0.2 L/cm H20
  • Total 0.1 L/cm H20
• Measurement of how easy or hard it is to
  inflate the lungs.
• COMPLIANCE IS RECIPROCAL OF
  ELASTANCE.
      Increased Lung Compliance
•   Easier to inflate the lung
•   Lower inflation pressures
•   Decreased Elastance
•   Causes
    • Emphysema
          Decreased Compliance
• Higher inflation pressures
    • Higher airway pressures on the ventilator
    • Increased complications (barotrauma, decreased CO)
•   Harder to inflate the lung
•   “Stiff lung”
•   Increased Elastance
•   Causes
     • Atelectasis
     • Fibrosis
     • Pneumothorax
     • ARDS
                  Lung Injury
• Acute Lung Injury (ALI)
  • Normal barriers to fluid movement within the lungs
    is disrupted.
  • If it is severe enough to cause acute hypoxemic
    respiratory failure it is termed:
• Acute respiratory distress syndrome
  (ARDS)
  • Most severe gas exchange abnormalities
  • Multiple Organ Dysfunction Syndrome (MODS)
          Lung Injury
• Normal  ALI            ARDS
       Clinical Spectrum
              Historical Look
• ARDS was referred to as “Shock Lung
  Syndrome”.
• Disease first identified in WWII.
• Many different names in the literature:
  • Da Nang Lung
  • Shock Lung Syndrome
  • Wet lung/White lung/Capillary Leak Syndrome
  • Non-cardiogenic pulmonary edema
  • Adult Hyaline Membrane Disease
          Diagnosis of ARDS
• Acute Process
• Bilateral Infiltrates
• PCWP less than 18 mm Hg
  • Non-Cardiogenic
• PaO2/FiO2 ratio less than or equal to 200
  Criteria Differentiating ALI and
                ARDS
• PaO2/FiO2 ratio
• Example
  • 100 mm Hg/.21 = 476
  • As the number decreases, oxygenation is
    getting worse
• ALI is when the ratio is LESS THAN 300
• ARDS the ratio LESS THAN 200
       Clinical Course in ARDS
• Initial Injury
• Apparent Respiratory Stability
  • X-rays and BS normal
  • Tachypnea, tachycardia, cough
• Respiratory Deterioration
  • Begins around 24 hours after initial insult
  • Peaks at 48-72 hours
• Recovery Process
                     Etiology
• DIRECT INJURY          • INDIRECT INJURY


•   Gastric Aspiration   • Sepsis
•   Near Drowning        • Cardiopulmonary
                           bypass
•   Fat or air emboli    • Burns
•   Smoke Inhalation     • Thoracic trauma
•   Pneumonia            • Massive blood
•   O2 Toxicity            transfusion
                         • Pancreatitis
     Acute Respiratory Distress
            Syndrome
• Injury of the lung
• Destruction of the alveolar-capillary
  membrane
• Engorged capillaries
• Interstitial and alveolar edema
• Hemorrhage
• Decreased surfactant with atelectasis
• Hyaline Membrane formation
• Fibrosis
     Pathological Abnormalities
• Exudative phase (3 - 7 days)
  • Edema, hyaline membrane formation, damage
    to type I cells, capillary damage
• Fibroproliferative phase (7 days - ?)
  • Regeneration of alveolar epithelium.
  • Fibroblasts mediate the formation of alveolar
    and interstitial fibrosis develops.
  • The extent of fibrosis determines the degree of
    pulmonary disability in patients who survive.
          Anatomic Alterations
• On examine, lungs appear:
  • “red”, “beefy”, or “liver-like” in appearance &
    heavy and hemorrhagic.
• Restrictive lung disease
  • “Baby Lungs”
• Low lung compliance – difficult to ventilate
  • Stiff lungs
  • High ventilator pressures needed.
• Refractory hypoxemia
  • Shunting
Lapinsky & Mehta, Critical Care 2005 9:1 (60-65)
              Clinical Findings
•   Tachypnea
•   Decreased lung volumes
•   Cyanosis
•   Increased shunting
•   Retractions
•   Dull percussion note & bronchial BS
                Chest X-ray
• Radiopaque – white
• The more severe the ARDS, the whiter the
  lungs appear
• Often described as “White Out” or diffuse
  “fluffy” infiltrates
  • Non-homogenous
  • “Baby Lungs”
• Heart size is normal
• Air Bronchograms
• Honeycombing or Ground Glass
      Complications of ARDS
• Nosocomial Infections
• Pulmonary emboli
• Oxygen Toxicity
• GI hemorrhage/gastric distension
• Sepsis, microemboli, Disseminated
  Intravascular Coagulation (DIC), anemia
• Pulmonary fibrosis – permanent
  disability
• Cardiovascular Problems
Multiorgan Failure in ARDS
              Management
• Reversal of underlying associated
  disorder
• Oxygen & Diuretics (keep on dry side)
• Steroids (after 7 days if no infection)
• Antibiotics
• Mechanical Ventilation
• Proning
• Nutritional support
                    Management
• Minimize O2 demand by reducing metabolic rate
   • Control fevers
   • Control anxiety and pain
• Altered Style of Ventilation
   •   Bi-Level Ventilation (APRV)
   •   High frequency ventilation
   •   Recruitment Maneuvers
   •   Proning
• Experimental Treatments:
   • Nitric Oxide
   • Extracorporeal membrane oxygenation (ECMO)
   • Exogenous Surfactant Administration
                   Proning
• Should see improvement in 1 hour
  • Response should be significant
  • PaO2 improves from 60 – 100 mm Hg
• Works better in indirect ARDS
  • Pancreatitis
• May improve oxygenation but does not
  improve mortality
• Facial Edema can be severe
                      Recovery
• Extent of recovery depends on:
  • Severity of the initial lung injury
  • Influence of secondary forms of injury
     •   Oxygen toxicity
     •   Nosocomial infections
     •   DIC
     •   Barotrauma with mechanical ventilation
• Normal lung function after 1 year
• Residual effects may result in decreased
  flowrates and DLCO
              Mortality Rate
• Mortality rates have declined over the past
  two decades from 90% to 30 – 40%
     Indications for Mechanical
             Ventilation
• Acute Hypercapnic Respiratory Failure
  • Respiratory Acidosis
• Acute Hypoxemic Respiratory Failure
  • PaO2 less than normal
  • FiO2 greater than 60% oxygen
                    PEEP
• Set PEEP at lower infection point to recruit
  alveoli and keep them open
• Shunting will improve with improved PaO2
• PEEP may decrease blood pressure and
  cardiac output so monitor both closely
  • Do not allow oxygen delivery to decrease
        Ventilation Strategies
• Use higher PEEP levels (10 – 15 cm H20)
• Set low tidal volumes at 5-7 mL/kg
• KEEP ALVEOLAR (PLATEAU)
  PRESSURE LESS THAN 30 – 35 cm H20
• This may result in permissive hypercapnia.

								
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