Acute Respiratory Distress Syndrome (ARDS)

In this Audioboards episode, we take a comprehensive, evidence-based deep dive into the management of Acute Respiratory Distress Syndrome (ARDS). From initial recognition and diagnosis to advanced rescue therapies, we walk through the practical bedside approach used in modern critical care. Learn how to apply lung-protective ventilation, calculate and set appropriate tidal volumes, optimize PEEP, monitor plateau and driving pressures, implement permissive hypercapnia, and use prone positioning effectively. We also cover fluid management, sedation strategies, neuromuscular blockade, corticosteroids, nutrition, prevention of ICU complications, and when to escalate to ECMO. 

Transcript

Welcome back to Audioboards. Today we're diving deep into the management of Acute Respiratory Distress Syndrome, or ARDS. This episode is going to be highly practical and focused on the bedside decisions that actually improve outcomes. ARDS remains one of the most common causes of respiratory failure requiring ICU admission and mechanical ventilation. While numerous therapies have been studied over the years, only a handful have consistently demonstrated benefit. The key to successful management is understanding that ARDS treatment is primarily supportive. We are buying time for the lungs to heal while preventing further lung injury.

Before discussing management, let's briefly define ARDS. According to the Berlin Definition, ARDS develops within one week of a known clinical insult or worsening respiratory symptoms. Patients have bilateral pulmonary infiltrates on chest imaging that cannot be fully explained by pleural effusions, lobar collapse, or cardiac failure. The respiratory failure is not primarily due to hydrostatic pulmonary edema, and oxygenation impairment is classified according to the PAO2 over FIO2 ratio while receiving at least 5 cm H2O of PEEP or CPAP.

Mild ARDS corresponds to a PAO2 over FIO2 ratio between 201 and 300. Moderate ARDS is between 101 and 200. Severe ARDS is 100 or less.

The most common causes are pneumonia, sepsis, aspiration, trauma, pancreatitis, inhalational injury, massive transfusion, and severe viral infections. The first management step is always identifying and treating the underlying cause. If the patient has bacterial pneumonia, appropriate antibiotics are essential. If sepsis is driving ARDS, source control and sepsis management become critical. No ventilator strategy can compensate for uncontrolled underlying disease.

Once ARDS is recognized, what's the initial respiratory support strategy?

For patients who are not yet intubated, high-flow nasal cannula is generally preferred over conventional oxygen therapy. Typical starting settings are flow rates between 40 and 60 liters per minute with FIO2 adjusted to maintain oxygen saturation between 88 and 95 percent.

Patients should be monitored closely for increasing work of breathing, respiratory rates persistently above 30 to 35 breaths per minute, worsening hypoxemia, altered mental status, or hemodynamic instability. Delayed intubation is associated with worse outcomes.

If the patient requires intubation, lung-protective ventilation becomes the cornerstone of management.

The target tidal volume is 4 to 8 mL per kg predicted body weight, with 6 mL per kg predicted body weight being the standard starting point.

Importantly, predicted body weight is not actual body weight.

For males:

PBW = 50 + 2.3 × (height in inches − 60)

For females:

PBW = 45.5 + 2.3 × (height in inches − 60)

For example, a 70-inch male has a predicted body weight of approximately 73 kg, giving a target tidal volume around 440 mL.

What pressures should we be monitoring?

This is where many clinicians make mistakes.

The plateau pressure should be maintained below 30 cm of H2O.

If plateau pressure exceeds 30 cm H2O, tidal volume should be reduced toward 4 mL per kg predicted body weight if necessary.

Driving pressure, which equals plateau pressure minus PEEP, should ideally remain below 15 cm of H2O. Studies consistently show increasing mortality as driving pressure rises.

Another important parameter is respiratory rate. To compensate for low tidal volume ventilation, respiratory rates are commonly increased to 20 to 35 breaths per minute. However, rates above 35 may increase dynamic hyperinflation and mechanical power delivered to the lung.

How should oxygenation targets be managed?

The goal is not normal oxygenation.

Most guidelines recommend targeting:

SpO2: 88% to 95%

PaO2: 55 to 80 mmHg

We deliberately avoid excessive oxygen exposure because hyperoxia may contribute to oxidative injury.

Similarly, permissive hypercapnia is acceptable.

Most clinicians tolerate:

pH > 7.20

Some centers accept pH as low as 7.15 if lung protection is maintained.

Contraindications to severe hypercapnia include elevated intracranial pressure, significant pulmonary hypertension, severe right ventricular failure, and certain arrhythmias.

What about PEEP?

PEEP is one of the most important components of ARDS management.

Every ARDS patient should receive at least 5 cm H2O of PEEP, but most moderate and severe ARDS patients require significantly more.

Typical ranges are:

Mild ARDS: 5–10 cm H2O

Moderate ARDS: 10–15 cm H2O

Severe ARDS: 12–20 cm H2O

The ARDSNet FIO2-PEEP tables are commonly used.

For example:

FIO2 0.6 usually corresponds to PEEP 10–14 cm H2O.

FIO2 0.8 often requires PEEP 14–18 cm H2O.

FIO2 1.0 may require PEEP 18–24 cm H2O in selected patients.

However, PEEP must be individualized. Increasing PEEP may improve oxygenation but can also reduce venous return and cause hypotension. Blood pressure, cardiac output, urine output, and compliance must be monitored carefully.

When should prone positioning be used?

Prone positioning is one of the strongest evidence-based interventions in ARDS.

Current practice is to prone patients with:

PAO2 over FiO2 ratio less than 150

FIO2 at least 0.6

PEEP at least 5 cm H2O

Proning sessions should last at least 16 consecutive hours daily.

Many centers continue proning until the patient achieves:

PAO2 over FiO2 ratio greater than 150 to 200

FiO2 less than 60%

PEEP less than 10 cm H2O

Benefits include improved ventilation-perfusion matching, reduced overdistension, better secretion clearance, and mortality reduction.

When should neuromuscular blockade be considered?

Neuromuscular blockade should not be routine.

However, it is reasonable in severe ARDS when there is:

Persistent ventilator dyssynchrony

Plateau pressure elevation

Excessive spontaneous respiratory effort

Failure of proning due to patient movement

Severe hypoxemia despite deep sedation

When used, continuous infusion is typically limited to approximately 24 to 48 hours to minimize ICU-acquired weakness.

Let's talk about fluid management.

After shock has resolved, a conservative fluid strategy is recommended.

The FACTT trial demonstrated more ventilator-free days with conservative fluid management.

Practical goals include:

Central venous pressure less than 4 mmHg when monitored

Avoid unnecessary maintenance fluids

Daily fluid balance near neutral or negative

Use loop diuretics when hemodynamically appropriate

Even a few liters of excess fluid can significantly worsen pulmonary edema.

What about corticosteroids?

Current evidence supports corticosteroids in many patients with moderate-to-severe ARDS.

Common regimens include:

Dexamethasone:

20 mg IV daily for 5 days

Then 10 mg IV daily for 5 days

Alternative protocols may use methylprednisolone, but dexamethasone is commonly used due to available evidence.

Patients should be monitored for hyperglycemia, secondary infection, delirium, and neuromuscular weakness.

How should sedation be approached?

Use the lightest sedation possible while maintaining ventilator synchrony.

Common targets:

RASS -1 to -2 in stable patients

RASS -4 to -5 during proning or paralysis

Daily awakening trials should be performed whenever feasible.

Excessive sedation prolongs mechanical ventilation and increases delirium risk.

What supportive ICU measures should never be forgotten?

Every ARDS patient should receive:

Venous thromboembolism prophylaxis

Stress ulcer prophylaxis when indicated

Early enteral nutrition within 24–48 hours

Pressure injury prevention

Glucose control targeting approximately 140–180 mg/dL

Delirium prevention strategies

Physical therapy and mobilization when feasible

These measures often have as much impact on outcome as advanced ventilator adjustments.

When should ECMO be considered?

ECMO should be considered early rather than as a last-minute rescue.

Typical triggers include:

PAO2 over FiO2 less than 80 despite optimal management

FiO2 100% with severe hypoxemia

Persistent severe respiratory acidosis with pH less than 7.20 despite lung-protective ventilation

Plateau pressures remaining dangerously elevated despite optimization

Before ECMO, ensure the patient has already received:

Low tidal volume ventilation

Appropriate PEEP

Neuromuscular blockade when indicated

Prone positioning

Optimization of fluid status

Treatment of the underlying disease

Can you leave us with a practical bedside algorithm?

Absolutely.

When you encounter ARDS, think:

Treat the underlying cause.

Target SpO2 88–95%.

Use tidal volume 6 mL/kg predicted body weight.

Keep plateau pressure below 30 cm H2O.

Keep driving pressure below 15 cm H2O.

Accept permissive hypercapnia if pH remains above approximately 7.20.

Use adequate PEEP based on oxygenation requirements.

Prone early when PAO2 over FiO2 falls below 150.

Maintain conservative fluid management after shock resolution.

Use neuromuscular blockade selectively for severe dyssynchrony or refractory hypoxemia.

Provide DVT prophylaxis, nutrition, delirium prevention, and early mobilization.

Consider ECMO when severe hypoxemia persists despite optimal conventional therapy.

If you consistently follow these parameters, you're applying the evidence-based principles that have repeatedly been shown to improve outcomes in ARDS and minimize ventilator-induced lung injury.  

Thanks for listening to AudioBoards. Stay tuned for more educational content in our next episode! The views and opinions expressed on the AudioBoards Podcast do not necessarily reflect those of our employers. This podcast is for educational purposes only and should not be used to diagnose or treat any medical conditions. It is not a substitute for professional medical advice. Always consult a qualified, board-certified healthcare provider for any medical concern.