Definition: ARDS is an acute, diffuse inflammatory form of lung injury characterized by poor oxygenation, bilateral pulmonary infiltrates, and acute onset. This disorder is associated with capillary endothelial injury and diffuse alveolar damage. 

Berlin Criteria for ARDS: 

1. Acute Hypoxic Respiratory Failure with P/F Ratio of less than 300 
2. Acute onset (within 7 days) of lung injury with new or worsening symptoms within that time frame
3. Bilateral opacities on imaging that are NOT explained by cardiac failure 
4. Cardiac failure is not the primary cause of acute hypoxic respiratory failure

Causes: Inhalants (smoke, chemical inhalation), infections (pneumonia), aspiration, drowning, pancreatitis, blood transfusions (TRALI), large bone fracture (fat emboli), sepsis, eosinophelic pneumonia, medications (chemotherapy or radiation), trauma, sickle cell. 

Symptoms: Wheezing, crackles, low oxygen saturation, tachycardia, pleuritic chest pain, fever, fatigue, tachypnea, confusion, cough. 

Pharmacologic Treatment: Steroids, neuromuscular blockade, and medical treatment of underlying cause. 

Note: As of Jan 2024, steroids and neuromuscular blockade (For severe ARDS only and for 48 hours or less) are new recommendations from the original 2017 guidelines. 

https://www.jwatch.org/na56980/2024/01/16/managing-acute-respiratory-distress-syndrome

Nonpharmacologic: Invasive or non-invasive oxygen delivery, prone position, drive pressure targeted PEEP,  ECMO

Guidelines: European Society of Critical Care Medicine (2017) 

 Updates are from American Thoracic Society (January 2024) 

For non-intubated patients with ARDS: Use high flow nasal cannula instead of conventional oxygen therapy to reduce risk of intubation (Strong recommendation, moderate evidence). 

For intubated patients with ARDS: use low tidal volume, 4-8 ml/kg ideal body weight (Strong recommendation, high evidence) 

Do NOT use prolonged recruitment maneuvers (strong recommendation, moderate level of evidence) or brief high pressure recruitment maneuvers (weak recommendation, high level of evidence)

Use Prone position for > 12 hours per day to reduce mortality (strong recommendation, high level of evidence). This is recommended for patients especially with P/F < 150.

Do NOT routinely use continuous infusions of neuromuscular blockade to reduce mortality (strong recommendation, moderate level of evidence) 

As above, this was slightly adjusted in Jan 2024 and a short course (<48 hours) is recommended in severe ARDS only. 

Refer patients who meet criteria for ECMO to ECMO centers (Strong recommendation, moderate evidence) 

Use of steroids is recommended as of January 2024. The steroid option, dose, and duration are not specified. 

PHARMACOLOGY 

Steroids:

Dexamethasone: 6-12 mg IV daily. Glucocorticoid with a half life of 3-4 hours in the plasma, but has a biological half life of 36-54 hours. Causes potent inflammatory inhibition and decreases swelling and mucous production in the airways. 

Hydrocortisone: 200 mg IV daily in divided doses. Half life of 1.5-2 hours with long biological half life (12 hours). Causes potent inflammatory inhibition and decreases swelling and mucous production in the airways.

Medications to avoid: 

Prolonged Neuromuscular blockade (> 48 hours) 

Random Dan Advice: 

• Remember to treat the underlying cause. ARDS is a generic term and ARDS caused by high triglycerides and pancreatitis is different from ARDS caused by CAP pneumonia. All of the above strategies are meant to buy you time and are not really for curing ARDS. 
• Get in the habit of looking at plateau pressures on ALL vented patients. It’s an easy push of a button and becomes much more relevant when you have a true ARDS patient with noncompliant lungs. 
• Don’t get fixated on the pH and hypercapnia. For severe cases especially, that pH of 7.27 is not going to kill the patient. Increasing their tidal volume even little could lead to a pneumothorax, and that could kill them. 
• Hypoxia… has been studied a lot. HOT-ICU, ICU-ROX, LOCO2, ,OXYGEN-ICU are some of the bigger ones with varying goals of conservative hypoxia (let the patient drift down with their sats or PaO2....maybe too much O2 is bad) VS standard of care (pick a reasonable O2 goal and shoot for that). Oxygen-ICU says lower O2 goals improve survival, ICU ROX says that conservative VS liberal O2 does nothing, LOCO2 says no one dies from low O2, but you may kill the patient’s gut, and Hot ICU also says conservative O2 VS liberal O2 doesn’t make a difference. The bottom line is this; just pick a practical target for PaO2 or sats, and do what you have to to get there. Some hypoxia is probably not bad 
• If you need steroid advice, much of this comes from COVID trials and recent CAP recommendations. The COVID dose (RECOVERY Trial) was 6 mg daily and a follow up (COVID STEROID 2 Trial) compared 12 mg to 6 mg and found a slight benefit with the higher dose, although statistically not significant.  A recent trial in NEJM (March 2023) looked at hydrocortisone for severe CAP and used 200 mg daily for 4-7 days depending on how the patient improved, followed by a taper.  

Recent evidence for/against some of the above: 

https://www.nejm.org/doi/full/10.1056/NEJMoa1800385 (NEJM March 2018) 

RECOVERY Trial: https://www.nejm.org/doi/full/10.1056/NEJMoa2021436 (NEJM July 2020)

COVID STEROID 2 Trial:12 mg dexamethasone daily VS 6 mg for COVID 

https://jamanetwork.com/journals/jama/fullarticle/2785529 (JAMA Oct 2021) 

Hydrocortisone in Severe Community Acquired Pneumonia (NEJM March 2023)

Use of steroids VS placebo in severe CAP  

https://www.nejm.org/doi/full/10.1056/NEJMoa2215145

ARDSNET Study: 6ml/kg ideal body weight VS 12 ml/kg ideal body weight in patients with ARDS. (NEJM May 2000)

https://www.nejm.org/doi/full/10.1056/NEJM200005043421801

Neuromuscular Blockers in Early ARDS: https://www.nejm.org/doi/full/10.1056/NEJMoa1005372 (NEJM 2010)