What are the most common causes of ARDS?

The most common causes include sepsis (most frequent), severe pneumonia, aspiration of gastric contents, trauma, acute pancreatitis, massive blood transfusion (TRALI), inhalational injury, and near drowning.

How is ARDS diagnosed?

ARDS is diagnosed using the Berlin criteria, which require acute onset within one week, bilateral pulmonary opacities on imaging, respiratory failure not explained by cardiac causes or fluid overload, and impaired oxygenation assessed by PaO2/FiO2 ratio with PEEP ≥5 cm H2O.

How is ARDS severity classified?

ARDS severity is classified based on PaO2/FiO2 ratio: mild (200–300), moderate (100–200), and severe (<100), all measured with PEEP ≥5 cm H2O.

What is the hallmark pathophysiology of ARDS?

The hallmark is diffuse alveolar damage resulting in increased capillary permeability, protein-rich alveolar edema, surfactant dysfunction, alveolar collapse, ventilation–perfusion mismatch, and refractory hypoxemia.

How is ARDS different from cardiogenic pulmonary edema?

ARDS is characterized by non-cardiogenic pulmonary edema with normal left ventricular filling pressures, whereas cardiogenic pulmonary edema results from heart failure with elevated cardiac filling pressures.

What is the cornerstone of ARDS management?

The cornerstone of ARDS management is lung-protective mechanical ventilation using low tidal volumes (6 mL/kg predicted body weight) and limiting plateau pressures to less than 30 cm H2O.

Why is low tidal volume ventilation important in ARDS?

Low tidal volume ventilation reduces ventilator-induced lung injury, decreases alveolar overdistension, and has been proven to reduce mortality in ARDS patients.

What role does PEEP play in ARDS management?

Positive end-expiratory pressure prevents alveolar collapse, improves oxygenation, reduces shunt, and helps maintain functional residual capacity in ARDS.

When is prone positioning indicated in ARDS?

Prone positioning is indicated in moderate to severe ARDS (PaO2/FiO2 <150) and should be applied for at least 16 hours per day to improve oxygenation and survival.

Is permissive hypercapnia allowed in ARDS?

Yes, permissive hypercapnia is allowed to maintain lung-protective ventilation, provided there are no contraindications such as raised intracranial pressure or severe metabolic acidosis.

What is the role of neuromuscular blockers in ARDS?

Short-term neuromuscular blockade may be used in early severe ARDS to improve ventilator synchrony, reduce oxygen consumption, and improve oxygenation.

Are corticosteroids useful in ARDS?

Corticosteroids may be beneficial in early moderate to severe ARDS to reduce inflammation and duration of mechanical ventilation, though timing and patient selection are important.

What fluid strategy is recommended in ARDS?

A conservative fluid management strategy is recommended once shock has resolved, as it improves lung function and reduces ventilator days without increasing organ failure.

When should ECMO be considered in ARDS?

Extracorporeal membrane oxygenation should be considered in severe ARDS with refractory hypoxemia despite optimal lung-protective ventilation, prone positioning, and neuromuscular blockade.

What are common complications of ARDS?

Common complications include ventilator-associated pneumonia, barotrauma such as pneumothorax, multi-organ dysfunction, ICU-acquired weakness, and long-term pulmonary fibrosis.

What is the mortality rate of ARDS?

The overall mortality rate ranges from 30 to 45 percent and increases with disease severity, advanced age, sepsis as the underlying cause, and presence of multi-organ failure.

Can patients recover fully from ARDS?

Many patients recover good lung function, but some develop long-term sequelae such as reduced diffusion capacity, exercise intolerance, pulmonary fibrosis, and neurocognitive impairment.

How can ARDS be prevented in ICU patients?

Prevention includes early treatment of sepsis, lung-protective ventilation in all mechanically ventilated patients, aspiration precautions, judicious fluid therapy, and avoidance of unnecessary blood transfusions.

What is the most important prognostic factor in ARDS?

Severity of hypoxemia as measured by the PaO2/FiO2 ratio, along with the underlying cause and presence of multi-organ failure, are the most important prognostic factors.

Acute Respiratory Distress Syndrome Clinical Features Diagnosis and Management Guide

Q: What is Acute Respiratory Distress Syndrome (ARDS)?

Acute Respiratory Distress Syndrome is a severe form of acute hypoxemic respiratory failure caused by diffuse inflammatory injury to the alveolar–capillary membrane, leading to non-cardiogenic pulmonary edema, decreased lung compliance, and refractory hypoxemia.

Q: What is the hallmark pathophysiology of ARDS?

The hallmark is diffuse alveolar damage resulting in increased capillary permeability, protein-rich alveolar edema, surfactant dysfunction, alveolar collapse, ventilation–perfusion mismatch, and refractory hypoxemia.

Q: How is ARDS different from cardiogenic pulmonary edema?

ARDS is characterized by non-cardiogenic pulmonary edema with normal left ventricular filling pressures, whereas cardiogenic pulmonary edema results from heart failure with elevated cardiac filling pressures.

Q: What is the cornerstone of ARDS management?

The cornerstone of ARDS management is lung-protective mechanical ventilation using low tidal volumes (6 mL/kg predicted body weight) and limiting plateau pressures to less than 30 cm H2O.

Q: Why is low tidal volume ventilation important in ARDS?

Low tidal volume ventilation reduces ventilator-induced lung injury, decreases alveolar overdistension, and has been proven to reduce mortality in ARDS patients.

Q: What role does PEEP play in ARDS management?

Positive end-expiratory pressure prevents alveolar collapse, improves oxygenation, reduces shunt, and helps maintain functional residual capacity in ARDS.

Q: When is prone positioning indicated in ARDS?

Prone positioning is indicated in moderate to severe ARDS (PaO2/FiO2 <150) and should be applied for at least 16 hours per day to improve oxygenation and survival.

Acute Respiratory Distress Syndrome (ARDS)

1. Definition

Acute Respiratory Distress Syndrome (ARDS) is a life-threatening form of acute hypoxemic respiratory failure caused by diffuse inflammatory injury to the alveolar–capillary membrane, leading to non-cardiogenic pulmonary edema, severe ventilation–perfusion mismatch, and refractory hypoxemia.

2. Epidemiology

Common in ICU patients
Mortality: 30–45% (higher with severe ARDS, older age, sepsis)
Survivors may have long-term pulmonary and neuromuscular sequelae

3. Pathophysiology (Stepwise)

Trigger (direct or indirect lung injury)
Inflammatory cytokine release (TNF-α, IL-1, IL-6)
Endothelial + epithelial damage
↑ Capillary permeability → protein-rich alveolar edema
Surfactant dysfunction → alveolar collapse
↓ Lung compliance + ↑ shunt fraction
Severe hypoxemia refractory to oxygen

Phases

| Phase | Features |

| ----------------------------- | ---------------------------------- |

| Exudative (Days 1–7) | Edema, hyaline membranes |

| Proliferative (Days 7–21) | Type II pneumocyte hyperplasia |

| Fibrotic (>3 weeks) | Pulmonary fibrosis (some patients) |

4. Etiology / Causes

Direct Lung Injury

Pneumonia (bacterial, viral, COVID-19)
Aspiration of gastric contents
Inhalational injury (smoke, toxins)
Pulmonary contusion
Near drowning

Indirect Lung Injury

Sepsis (most common)
Severe trauma, shock
Acute pancreatitis
Massive blood transfusion (TRALI)
Burns
Drug overdose

5. Diagnostic Criteria (Berlin Definition)

All four must be present:

Timing:

Within 1 week of known clinical insult

Imaging:

Bilateral opacities on CXR/CT

(not fully explained by effusions, collapse, nodules)

Origin of edema:

Respiratory failure not due to cardiac failure or fluid overload

(Echo or hemodynamics if doubt)

Oxygenation (with PEEP ≥5 cm H₂O)

| Severity | PaO₂/FiO₂ |

| -------- | --------- |

| Mild | 200–300 |

| Moderate | 100–200 |

| Severe | <100 |

6. Clinical Features

Symptoms

Acute onset severe dyspnea
Tachypnea
Refractory hypoxemia
Restlessness, confusion

Signs

Cyanosis
Use of accessory muscles
Diffuse crackles
Hypotension (often with sepsis)

7. Investigations

Laboratory

ABG: Hypoxemia ± respiratory alkalosis
↑ Lactate (if sepsis)
CBC, CRP, procalcitonin (infection)
Renal & liver function (MODS)

Imaging

Chest X-ray: Bilateral diffuse infiltrates
CT chest: Ground-glass opacities, consolidation

Cardiac Evaluation

Echocardiography to exclude cardiogenic pulmonary edema

8. Differential Diagnosis

Cardiogenic pulmonary edema
Acute heart failure
Pulmonary embolism
Diffuse alveolar hemorrhage
Acute interstitial pneumonia
Pneumocystis pneumonia

9. Management (Cornerstone Section)

A. Treat Underlying Cause

Early broad-spectrum antibiotics for sepsis
Source control (drain abscess, stop transfusion)
Treat pancreatitis, trauma, aspiration

B. Oxygenation & Ventilatory Support

1. Low Tidal Volume Ventilation (LTVV) – GOLD STANDARD

Tidal volume: 6 mL/kg predicted body weight
Plateau pressure: <30 cm H₂O
Permissive hypercapnia allowed

2. PEEP Optimization

Prevent alveolar collapse
Moderate–high PEEP in moderate/severe ARDS

3. Prone Positioning

Indicated when PaO₂/FiO₂ <150
≥ 16 hours/day
Improves oxygenation and mortality

4. Neuromuscular Blockade

Short course (≤48 h) in severe ARDS
Improves ventilator synchrony

5. ECMO

Refractory hypoxemia despite optimal ventilation
Specialized centers only

C. Fluid Management

Conservative fluid strategy
Avoid positive fluid balance
Diuretics once shock resolved

D. Pharmacologic Therapy

Corticosteroids

Indication: Moderate–severe ARDS, especially early phase
Benefit: ↓ ventilation days, possible mortality benefit

Example:

Methylprednisolone 1–2 mg/kg/day (tapered)

⚠ Avoid late unregulated use

E. What is NOT Recommended

Routine pulmonary artery catheter
Routine nitric oxide
Routine β-agonists
High tidal volume ventilation

10. Drug Reference (Key Agents)

Sedatives (e.g., Propofol)

Indication: Ventilator synchrony
MOA: GABA-A agonist
Adverse effects: Hypotension, hypertriglyceridemia
Monitoring: BP, triglycerides

Neuromuscular Blockers (e.g., Cisatracurium)

MOA: Non-depolarizing NMJ blockade
Indication: Severe ARDS
Adverse effects: Prolonged weakness
Monitoring: TOF, ventilation

Antibiotics

Based on suspected source
Early empiric → de-escalate after cultures

11. Complications

Ventilator-associated pneumonia
Barotrauma (pneumothorax)
Multi-organ dysfunction
ICU-acquired weakness
Pulmonary fibrosis

12. Prognosis

Depends on:

* Severity (PaO₂/FiO₂)

* Age

* Cause (sepsis worse)

* Comorbidities

Survivors may have:

* Reduced DLCO

* Exercise intolerance

* PTSD, cognitive dysfunction

13. Prevention

Lung-protective ventilation in all ventilated patients
Aspiration precautions
Early sepsis management
Judicious blood transfusion

14. Key Exam & Clinical Pearls

ARDS = non-cardiogenic pulmonary edema
Low tidal volume ventilation saves lives
Prone positioning is underused but lifesaving
Oxygen alone is often insufficient
Always treat the underlying cause