Friday, March 31, 2017

ARDS pathophysiology Q&A

In Acute Respiratory Distress Syndrome (ARDS), what happens to the following parameters? (Increase / decrease / normal) 

Compliance
Pulmonary artery pressure
Pulmonary capillary wedge pressure
A-a gradient (Alveolar-arterial gradient)
PaO2 / FiO2

Answers given below!

Compliance decreases.
Damage to type II cells results in decreased production of surfactant with resultant decreased compliance and alveolar collapse.

Pulmonary artery pressure increases.
Pulmonary hypertension (PH) is widely recognized as a characteristic feature of ARDS. PH etiology includes parenchymal destruction and airway collapse, hypoxic pulmonary vasoconstriction, presence of other pulmonary vasoconstrictors and vascular compression.

Pulmonary capillary wedge pressure (Measure of left atrial pressure) is not elevated.
Pulmonary edema with normal PWP suggests a diagnosis of acute respiratory distress syndrome (ARDS) or non cardiogenic pulmonary edema (as in opiate poisoning).

A-a gradient (Alveolar-arterial gradient) increases.
High A-a gradients are associated with oxygen transfer/gas exchange problems. These are usually associated with alveolar membrane diseases, interstitial diseases, or ventilation/perfusion (V/Q) mismatch.

PaO2 / FiO2 decreases.
The ratio of partial pressure arterial oxygen and fraction of inspired oxygen, sometimes called the Carrico index, is a comparison between the oxygen level in the blood and the oxygen concentration that is breathed. This helps to determine the degree of any problems with how the lungs transfer oxygen to the blood. A PaO2/FiO2 ratio less than or equal to 200 is necessary for the diagnosis of acute respiratory distress syndrome.

ARDS treatment:
Low tidal volume - Causes low pulmonary pressures, prevents overdistension of alveoli.
PEEP - Prevents alveolar collapse at the end of expiration, decreases shunting and work of breathing

That's all!
-IkaN

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