Understanding ARDS

The understanding of ARDS starts with a solid foundation in histology … the study of tissue structure.

This is the pulmonary alveolar capillary functional unit.
The alveoli identified in pink.
The capillaries identified in red.
The pulmonary interstium identified in yellow. The pulmonary interstitial tissue is not functional structure… but rather tissue that holds functional tissue in place (ie the alveolus and the pulmonary capillary in place).
Here are the 3 major players in the lung … colorized.
We will see what happens when systemic hypotension requires aggressive fluid resuscitation in future slides.
Here are all components of the lung …colorized. When aggressive fluid resuscitation is initiated (ex. 20L of fluid) are administered (“hung”) 1L at a time over 8 hours, the fluid will start in the blood vessel and may end up in the pulmonary interstitial tissue making the interstitial very dense. Since the interstitial tissue is now dense and completely surrounding the alveolus, it acts to start compressing the alveolus with atelectasis soon to occur.
Aggressive fluid resuscitation with 20L of fluid over 8 hours will result in some of that fluid ending up in the pulmonary interstitium and become dense enough to cause atelectasis.
Soon the clinician will have problems of ubiquitous SEVERE ATELECTASIS.
Interstitial tissue dense with 20L of fluid surrounding the alveolus starting the atelectatic process.

As an analogy to normal vs. dense pulmonary interstitial tissue, angel food cake vs. rum cake is demonstrated.

Angel food cake : soft, compressible, rebounding cake.

Rum cake : dense, non re-bounding cake.

PEEP=3 alveolus soon to be crushed by pulmonary interstitial tissue pressure=5.
impending ATELE TASIS.
PEEP=5 alveolus wii maintain its integrity vs. pulmonary interstitial tissue pressure=5.
Alveolus to maintain itself…ok for now.
PEEP=9 alveolus soon to recruit other alveoli vs. pulmonary interstitial tissue pressure=5.
Alveolus in good shape with therapeutic PEEP applied.