View source for Acute respiratory distress syndrome

== Background ==

* Lung damage that occurs within one week of an insult, with bilateral CXR opacities, not explain by other causes
* Severity based on P:F ratio: severe &lt;100, moderate 100-200, and mild 200-300
* Lung protective ventilation [https://doi.org/10.1056/NEJM200005043421801 reduces mortality]
** V<s>T</s> 6mL/kg predicted body weight, plateau pressure ≤30 cmH<s>2</s>O, SpO2 88-95%, and pH 7.3-7.45

=== Definition ===

* Syndrome of diffuse alveolar and interstitial edema
* &quot;[https://doi.org/10.1007/s00134-005-2627-z Baby lung]&quot;: small effective lung volume, because the dependent portions are filled with fluid

===[https://doi.org/10.1001/jama.2012.5669 Berlin Definition (2012)]===

* Syndrome, not disease, per European task force in 2012
* Timing: within 1 week of a known insult
* Origin of edema: not cardiac or hydrostatic edema
* Chest imaging bilateral opacities not otherwise explained
* Severity based on oxygenation
** Mild: ratio of PaO<sub>2</sub>/FiO<sub>2</sub> between 200-300 with PEEP over 5 cmH<sub>2</sub>O (27% mortality)
** Moderate: ratio between 100 and 200 with PEEP over 5 cmH<sub>2</sub>O (32% mortality)
** Severe: ratio below 100 with PEEP over 5 cmH<sub>2</sub>O (45% mortality)

=== Etiologies ===

* Direct
** Pneumonia
** Aspiration
** Inhalational injury
** Pulmonary contusion
** Near-drowning
* Indirection
** Sepsis
** Major trauma
** Multiple blood product transfusions
** Pancreatitis
** Shock
** Drug overdose
** Amniotic fluid embolism

=== Pathophysiology ===

* Acute edema from neutrophil activation, with formation of hyaline membranes, and eventual fibrosis
* Type I pneumocytes replaced with type II
* Increased alveolar permeability leading to non-hydrostatic pulmonary edema
* Lungs become less compliant, due to a decrease in the available lung volume

== Clinical Manifestations ==

* Dyspnea and escalating ventilatory requirements following a known cause of ARDS

== Differential Diagnosis ==

* ARDS (50%)
* [[Pneumonia]] (25%)
* [[Pulmonary edema]] (11%)
* [[Invasive aspergillosis]] (6%)
* [[Pulmonary embolism]] (3%)
* Other (5%)

== Investigations ==

* Chest x-ray showing bilateral infiltrates
* Bronchoalveolar lavage (BAL)
** Excludes the diagnosis if less than 5% neutrophils (can be over 80% in ARDS)
** Suggestive if lavage to plasma protein ratio &gt; 0.7 (less than 0.5 in hydrostatic edema)

== Management ==

=== All Patients ===
* Lung-protective ventilation (see [[ARDS ventilation protocol]])
** Targets tidal volume of 6mL/kg predicted body weight, plateau pressure ≤30 cmH2O, SpO2 88-95%, and pH 7.3-7.45
** Decrease tidal volume from 8mL/kg to 6mL/kg predicted body weight over 4 hours, then continue to decrease in 1 mL/kg increments until plateau pressures &lt;30 or tidal volume 4mL/kg
* Maintain euvolemia

=== Moderate to Severe ARDS ===

* Higher PEEP over 15 cmH<sub>2</sub>O
* Permissive hypercapnia to CO<sub>2</sub> 60-70 and pH 7.2-7.25, if needed

=== Severe ARDS ===

* Prone positioning
* vv-[[ECMO]]

[[Category:Critical care]]
[[Category:Respirology]]