Surgical Critical Care: Acute Respiratory Distress Syndrome (ARDS)
Acute Respiratory Distress Syndrome (ARDS)
Berlin Criteria Mn
- Bilateral Opacities on Imaging
- Acute Onset < 7 Days
- PaO2:FiO2 < 300
- Not Fully Explained by CHF or Fluid Overload
Severity
- *Based on PaO2:FiO2 (P:F Ratio)
- Mild: P:F < 300
- Moderate: P:F < 200
- Severe: P:F < 100
Mortality
- Overall High Mortality (40%)
- Increases with Disease Severity
- Mild: 35%
- Moderate: 40%
- Severe: 46%
Causes
- Sepsis (Most Common Cause)
- Pneumonia (Most Common Community-Acquired Cause)
- Aspiration
- Trauma
- Massive Transfusion/Transfusion-Related Acute Lung Injury (TRALI)
- Pancreatitis
- Inhalation Injury
- Cardiothoracic Surgery
- Medications
Presentation
- Dyspnea
- Altered Mental Status
- Respiratory Distress
- Complications:
- Impaired Gas Exchange & Hypoxemia
- Most Common Long-Term Defect: Decreased Diffusion Capacity
- Decreased Lung Compliance
- Barotrauma
- Pulmonary Hypertension
- Impaired Gas Exchange & Hypoxemia
Phases
- 1st Phase: Exudative Phase
- Diffuse Alveolar Damage (DAD) Over the First 7-10 Days
- Effects:
- Necrosis & Sloughing of Type I Pneumocytes & Capillary Endothelium
- Loss of Tight Junctions that Prevent Fluid Movement
- Inflammatory Exudate (Protein Rich) Floods Alveoli – From Increased Vascular Permeability
- Lung Injury – From Leukocyte Proliferation
- Collapse & Shunting – From Surfactant Inhibition
- Hyaline Membrane Forms within Alveoli
- Necrosis & Sloughing of Type I Pneumocytes & Capillary Endothelium
- 2nd Phase: Fibroproliferative Phase
- Proliferation of Type II Pneumocytes After 7-10 Days
- Generally Lasts About 14-21 Days
- Effects:
- Early Collagen Formation
- Interstitial Infiltration of Myofibroblasts
- Decreased Compliance
- Still Reversible
- 3rd Phase: Fibrotic Phase
- Interstitial Fibrosis
- Not a Universal Outcome Seen in All Patients
- Associated with & Prolonged Mechanical Ventilation & Increased Mortality
Diagnosis
- Diagnosis: Clinical Diagnosis Based on the Berlin Criteria (Above)
ARDS 1
Acute Respiratory Distress Syndrome (ARDS) – Treatment
Primary Treatment
- Supportive Care
- Treat Underlying Pathology
- Conservative Fluid Management
- Improves Ventilator-Free & ICU-Free Days
- No Mortality Benefit
- Manage Patient-Ventilator Dyssynchrony
- Lung Protective Ventilation
Lung Protective Ventilation
- Definition: Ventilation with Low Tidal Volumes to Reduce Alveolar Overdistention & Barotrauma
- Improves Mortality for ARDS of All Severities
- Ventilation (Tidal Volume/Respiratory Rate)
- Initially Tidal Volume: 8 ml/kg x Ideal Body Weight (General Standard)
- Decrease Tidal Volume 1 ml/kg Every 1-2 Hours
- Goal Tidal Volume: 4-6 ml/kg x Ideal Body Weight
- Adjust Tidal Volume & Respiratory Rate for Goal Plateau Pressure ≤ 30 cm H2O
- Oxygenation (PEEP/FiO2)
- Oxygenation Goals: PaO2 55-80 mmHg or SpO2 88-95%
- Adjust PEEP to Required FiO2
- Initially Recommended to Start with Lower-PEEP Strategy
| FiO2 | 0.3 | 0.4 | 0.5 | 0.6 | 0.7 | 0.8 | 0.9 | 1.0 |
| PEEP | 5 | 5-8 | 8-10 | 10 | 10-14 | 14 | 14-18 | 18-24 |
- Consider High-PEEP Strategy if Refractory
| FiO2 | 0.3 | 0.4 | 0.5 | 0.6-0.7 | 0.8-0.9 | 1.0 |
| PEEP | 5-14 | 14-16 | 16-18 | 20 | 22 | 22-24 |
- Complications:
- Permissive Hypercapnia
- Respiratory Acidosis Allowed to Maintain Low Tidal Volumes
- PaCO2 Goal Not Well Defined
- Should Generally Maintain pH 7.25-7.50
- Patient-Ventilator Dyssynchrony
- May Require Increased Sedation
- *See Surgical Critical Care: Mechanical Ventilation – Patient-Ventilator Dyssynchrony
- Permissive Hypercapnia
Ancillary Measures
- Prone Positioning
- Mortality Benefit for Moderate-Severe ARDS
- No Mortality Benefit for Mild ARDS
- *See Surgical Critical Care: Mechanical Ventilation – Ventilator Management
- Mortality Benefit for Moderate-Severe ARDS
- Inhaled Vasodilators (Nitric Oxide/Prostacyclin)
- Improves Oxygenation but No Proven Morbidity/Mortality Benefit
- *See Surgical Critical Care: Mechanical Ventilation – Ventilator Management
- Paralysis/Neuromuscular Blockade
- Early Short-Term (48 Hour) Paralytics May Improve Mortality in Severe ARDS (Debated with Conflicting Results)
- Extracorporeal Membrane Oxygenation (ECMO)
- Alternative Modes of Ventilation:
- Airway Pressure Release Ventilation (APRV)
- High-Frequency Oscillatory Ventilation (HFOV)
- *See Surgical Critical Care: Mechanical Ventilation – Settings & Modes
Mnemonics
Berlin Criteria for ARDS
- “ABC-3”
- Acute
- Bilateral Opacities
- CHF Not Fully Explained
- P:F < 300
References
- Santos LC, Abreu CF, Xerinda SM, Tavares M, Lucas R, Sarmento AC. Severe imported malaria in an intensive care unit: a review of 59 cases. Malar J. 2012 Mar 29;11:96. (License: CC BY-2.0)