Acute Respiratory Distress Syndrome(ARDS)

Acute Respiratory Distress Syndrome is a secondary illness of lungs which is due to underlying primary Lungs injury. ARDS is an emergency medical condition which required immediate mechanical ventilation. Prognosis of ARDS is very poor nearly about 40%, even after recovery also the quality of life decreases.

Cause/Etiology of ARDS

ARDS is caused by any direct or indirect injury to lungs

1. TRALI (Transfusion induced acute lung injury)
2. Pneumonia
3. Sepsis
4. Diffuse injury
5. Trauma
6. pancreatitis

Pathophysiology of ARDS

In responding to lung injury inflammation process started in the body which leaks fluid into the small sac of the lung called alveoli. Fluid-filled alveoli affect oxygen and carbon dioxide exchange, which may lead to tissue hypoxia and death.

Diagnosis of ARDS

Chest Radiography, Chest CT, ABG, and PaO₂ /FiO₂ ratio

For know more about ABG please click below

Arterial Blood Gas CLICK HERE

PaO₂/FiO₂ ratio for diagnosis of ARDS

PaO₂ is Partial Pressure of oxygen and FiO₂ is Fraction of inspired oxygen. These 2 have greater role in the diagnosis of ARDS.

Severity of ARDS	PaO2 / FiO2	Mortality
Mild ARDS	201 to 300	Approx 27%
Moderate ARDS	101 to 200	Approx 32%
Severe ARDS	<100	Approx 45%

Example 1 – Patient is on vent support, his FiO₂ is set on 80% and his PaO₂ in ABG is 60mmHg.

Then PaO₂ / FiO₂ is 60/0.8 = 75, I.epatient having Severe ARDS

Example 2 – A patient is on Oxygen mask 8 litter/min and his PaO₂ in ABG shows 65mmHg.

Then PaO₂ / FiO₂ is 65/0.53 = 122, I.e the patient is having Moderate ARDS

Tip – In Oxygen mask 1 litter of oxygen is equal to 4% and always remember air has 21% of oxygen, so in the above equation, the patient is on 8lt of oxygen that means 8*4 = 32% and air having 21% so 32+21 = 53%.

Ventilator Settings in ARDS

Mechanical ventilation is necessary for moderate and severe Acute Respiratory Distress Syndrome. The rule is High PEEP(Positive end-expiratory pressure) and Low tidal volume(4 to 6ml per kg body weight). High peep is helping to keep open alveoli and prevent from collapse after expiration and in pause state; It makes the exchange of carbon dioxide and oxygen going on `without disruption even during expiration and pause state.

Low tidal volume is very necessary to prevent lungs from secondary trauma because in Acute Respiratory Distress Syndrome lungs capacity decreases due to fluid accumulation.

If saturation is still not improving then ECMO(Extracorporeal membrane oxygenation) is the only option.

For more information Visit my YouTube Channel

www.youtube.com/c/Healthbeats