Editing Acute respiratory distress syndrome


Acute respiratory distress syndrome (ARDS) is an acute, diffuse, inflammatory form of lung injury that is associated with a variety of aetiologies.

== Pathophysiology ==

* Characterised by rapid onset of widespread lung inflammation
* Loss of aerated lung tissue:
** Endothelial cell injury and pulmonary vascular permeability leading to flooding of alveoli
** Lung oedema
** Gravity-dependent atelectasis
* Outcomes:
** Increased shunting
** Increased alveolar dead space
** Decreased lung compliance
* Stages
** Early exudative stage
** Fibroproliferative stage
** Fibrotic stage 

== Diagnosis: ==

* ''Previously used Berlin criteria, new consensus guidelines 2024''
* Suspect in patients with progressive dyspnoea, increasing O2 requirement, and bilateral alveolar infiltrates on chest imaging within one week of an inciting event.
* Chest signs - dyspnoea, tachycardia, diffuse crackles (severe: confusion, WOB, cyanosis, diaphoresis)
* ABG: hypoxaemia, with acute resp alkalosis, and elevated A-a gradient
** Acute hypercapnoeic resp acidosis is ominous sign - pre-arrest
** Other signs of underlying aetiology may be present
* Exclude acute cardiogenic pulmonary oedema - can base this off hx/ex/BNP (low BNP favours ARDS)

== Ix: ==

* FBE/UEC/CMP/LFT/COAGS/ABG
* CXR/ECG
* MICRO

== Severity: ==

* Mild ARDS: PaO2/FiO2 > 200 and <300 on vent (PEEP or CPAP >=5cm H20)
* Mod: PaO2/FiO2 100-200, PEEP >5cm H20
* Severe: PaO2/FiO2 < 100, PEEP >5cm H20

Can use SpO2 % if ABG unavailable

== Management ==

* Oxygen via mechanical ventilation with PPV, initially lung-protective
* Conservative fluid balance
* Prone positioning for severe ARDS

== Aetiology ==
ARDS has over 60 etiologies. This is an abbreviated list of the common causes of ARDS.
{| class="wikitable"
|'''Etiology'''
|'''Clinical features'''
|'''Diagnostic tests'''
|-
|Sepsis
|Fever hypotension, leukocytosis, lactic acidosis, infectious source
|Appropriate clinical context and positive cultures
|-
|Aspiration pneumonitis
|Witnessed or risk for aspiration, food, lipid laden macrophages, airway erythema on bronchoscopy
|Presumptive diagnosis with negative cultures
|-
|Infectious pneumonia (including mycobacterial, viral, fungal, parasitic)
|Productive cough, pleuritic pain, fever, leukocytosis, lobar consolidation or bilateral infiltrates in an immunosuppressed patient
|Appropriate clinical context and positive respiratory cultures
|-
|Severe trauma and/or multiple fractures
|History of trauma or fractures within the last week
|Diagnosis is apparent
|-
|Pulmonary contusion
|History of chest trauma (blunt or penetrating), chest pain
|Presumptive diagnosis in the correct clinical context, negative cultures
|-
|Burns and smoke inhalation
|Exposure to fire or smoke, cough, dyspnea, DIC, particulate matter on bronchoscopy, surface burns
|Presumptive diagnosis in the correct clinical context, negative cultures
|-
|Transfusion related acute lung injury and massive transfusions
|History of transfusion, dyspnea during or shortly after transfusion
|Diagnosis of exclusion
|-
|HSCT¶
|History of HSCT
|Diagnosis of exclusion
|-
|Pancreatitis
|Abdominal pain, vomiting, risk actors (eg, gallstones, alcohol, viral infection)
|Elevated amylase and lipase, with or without abnormal imaging
|-
|Inhalation injures other than smoke (eg, near drowning, gases)
|History of inhalation exposure (eg, chlorine gas)
|Diagnosis of exclusion
|-
|Thoracic surgery (eg, post-cardiopulmonary bypass) or other major surgery
|History of surgery, intraoperative ventilation, intraoperative transfusion
|Diagnosis of exclusion
|-
|Drugs (chemotherapeutic agents, amiodarone, radiation)
|New drugs or radiation exposure on history, lymphocytosis on lavage, lavage may have suggestive features of amiodarone toxicity ("foamy macrophages") but is nonspecific
|Diagnosis of exclusion, lung biopsy occasionally helpful
|}


Some patients remain ventilator-dependent during fibroproliferative phase

* Radiographically: progression from airspace opacification to coarser, reticular pattern of lung infiltration
* Persistent hypoxaemia, low lung compliance, high dead space, progressive pulmonary hypertension
* Differentiate from VAP or ventilator-induced lung injury

== Complications: ==

* Barotrauma
** PEEP stress
* Nosocomial infection
* Delirium
* VTE
* GI bleeding (stress ulcers)
* Poor nutrition

[[Category:Respiratory]]
[[Category:Critical care]]