Acute respiratory distress syndrome Flashcards
What is Acute Respiratory Distress Syndrome (ARDS)?
non-cardiogenic pulmonary oedema and diffuse lung inflammation syndrome that often complicates critical illness
Must fulfill 3 criteria:
- acute onset
- bilateral opacities seen on chest xray
- PaO₂/FiO₂ (arterial to inspired oxygen) ratio of ≤300 on positive end-expiratory pressure (PEEP) or continuous positive airway pressure (CPAP) ≥5 cm H₂O
What are the risk factors for ARDS?
Alveolar side
- aspiration
- pneumonia
-
severe trauma
- indirect injury from early haemorrhagic shock
- later onset of multiple organ failure
- Pulmonary contusions
- long bone fractures
- multiple transfusions of blood products
- burns
- smoke inhalation
- drowning
- lung transplant
capillary side
- sepsis
- blood transfusions
- pancreatitis
-
history of alcohol misuse
- due to depletion of endogenous antioxidants
If no risk factors for ARDS are present, but presentation looks similar, what must be ruled out?
- Pulmonary oedema secondary to heart failure
- diffuse alveolar haemorrhage due to pulmonary vasculitis
- collagen vascular disease
- acute eosinophilic pneumonia
What is the aetiology of ARDS?
- mainly sepsis of a pulmonary cause e.g. pneumonia
- also aspiration
- cardiopulmonary bypass
- fat embolism
- disseminated intravascular coagulation
- drug overdose
- see other risk factors
Summarise the epidemiology of ARDS
- 10-15% of patients admitted to ICU meet criteria
- mortality of ARDS = 40-50%
- patients with ARDS due to sepsis generally have the highest mortality
What are the presenting symptoms of acute respiratory distress syndrome?
-
acute onset of SOB
- & hypoxaemia
- cough
- w expectoration of frothy pulmonary oedema
What are the signs of ARDS on physical examination?
- acute hypoxic respiratory failure, refractory to O2 treatment
- Cyanosis
- Tachypnoea
- Tachycardia
- widespread inspiratory crepitations
- increased peak inspiratory pressure & end-inspiratory plateau pressure
- lung exam: basilar or diffuse rales
What primary investigations are required when ARDS is suspected?
- ABG - to calculate PaO2/inspired O2 ratio
-
Chest X ray
- to find infiltrates consistent w pulmonary oedema
-
Brain natriuretic peptide (BNP) levels
- >500ng most likely indicates HF
-
ECG
- if HF is still suspected & no risk factors for ARDS
-
Blood, sputum, urine cultures
- to find sepsis
-
Bronchoalveolar lavage (BAL) / endotracheal aspiration for Gram stain & cultures
- to identify suspected pneumonia / rule out mimicing conditions w bilateral infiltrates e.g. diffuse alveolar haemorrhage / acute eosinophilic pneumonia
What is an absolute method of distinguishing ARDS from HF?
pulmonary artery catheter (to estimate left ventricular end-diastolic pressure)
not indicated in all patients
What is usually seen on a chest X ray in ARDS?
Is CT of the thorax routinely indicated for suspected ARDS?
No, but has shown that dependent lung portions are most affected.
What other investigations are indicated for suspected ARDS?
nvestigations
-
CXR
o
Bilateral alveolar and interstitial
shadowing
-
Blood
o
FBC
o
UE
o
LFT
o
ESR/CRP
o
Amylase
o
Clotting
o
ABG
o
Blood clotting
o
Sputum culture
o
BNP to distinguish from heart
failure
-
Echocardiography
o
Severe aortic or mitral valve
dysfunction or decreased LVEF is
more indicative of haemodynamic
oedema than ARDS
-
Pulmonary artery catherterisation
-
Bronchoscopy
o
If cause cannot be determined
through Hx, to exclude differentials
o
Lavage fluid for microbiology
o
Cytology
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