Acute Respiratory Distress Syndrome (ARDS) for USMLE Step1 and USMLE Step 2

Handwritten lecture on Acute Respiratory Syndrome (ARDS) for USMLE Step 1 and USMLE Step 2. We will be reviewing pathophysiology, pathology, clinical symptoms and physical findings, diagnosis and evaluation and treatment.

PATHOPHYSIOLOGY OF ACUTE RESPIRATORY DISTRESS SYNDROME (ARDS)
Acute Respiratory Distress Syndrome (ARDS) occurs due to Acute Lung Injury leading to increase vascular permeability, edema and aeration.

Leakage of the blood vessels due to endothelial damage causes increase loss of fluid and protein starts off the process of Acute Respiratory Distress Syndrome. After lymphatics are overwhlemed the fluid enters the alveoli preventing oxygen diffusion. Eventually there is fibrosis around alveoli. Alveoli has high levels of Ineterleukin 8 and Neutrophils.

Damage to Type 2 cells decrease surfactant leading to alveolar collapse.

Acute Respiratory Distress Syndrome (ARDS) will have decrease gas exchange (V/Q mismatch), physiological shunting, and hypoxemia. Also decrease lung compliance is another feature of ARDS due to decrease area of aeration and fibrosis.

CAUSES OF ACUTE RESPIRATORY DISTRESS SYNDROME (ARDS) include sepsis, pneumonia, aspiration, severe trauma, long bone fractures (fat emboli), blood transfusion (greater than 15 units), stem cell transplant (graft failure). Medications such as aspirin, cocaine, opiods, phenothiazines during overdose. Protamine, Nitrofurantoin, chemotherapy have more idiosyncratic reactions. Other causes of acute respiratory distress syndrome (ARDS) include smoking, cardiopulmonary bypass, blood type A, acute pancreatitis, obesity, thoracic surgery.

CLINICAL SYMPTOMS OF ACUTE RESPIRATORY DISTRESS SYNDROME (ARDS)
Exudative Stage has diffuse alveolar damage and fluid accumulation leading to dyspnea, cyanosis diffuse crackles. eventually they will have high respiratory rate and chest pain.

Proliferative stage there is resolution of pulmonary edema causing increase alveolar type 2 cells causeing interstitial myofibroblasts. Symptoms improve unless they go to fibrotic stage.

Fibrotic stage of acute respiratory distress syndrome (ARDS) there is obliteration of normal lung architecture leading to diffuse fibrosis, cyst formation and require long term mechanical ventilation.

DIAGNOSIS of ACUTE RESPIRATORY DISTRESS SYNDROME (ARDS)
ABG shows high Aa gradient, Acute respiratory alkalosis.
Chest XRAY shows diffuse bilateral alveolar infiltrates. CT Scan shows widespread patchiness and air bronchogram.
Criteria for diagnosis of acute respiratory distress syndrome (ARDS) include symptoms within 1 week of inciting event, x-ray and CT opacities and rule out cardiogenic pulmonary edema. No murmurs, no increase in JVP, BNP should be low, PCWP should also be low in Acute Respiratory Distress Syndrome (ARDS).

PaO2 over FiO2
MILD is between 200 and 300
MODERATE is 100 to 200
SEVERE is less than 100

TREATMENT OF ACUTE RESPIRATORY DISTRESS SYNDROME
Give supplemental oxygen, hemodynamic support and treat underlying cause.

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