Okay, here is the last article in the Chest X-ray series for now. We will do a quick and very brief job at covering pulmonary vasculature. As a note, this lecture is largely anecdotal, meaning this is based upon personal experience and makes sense to me but was not learned directly from any single textbook but a mash up of multiple books, mentors, and my own observations.
Let’s talk about fluid overload in the lungs. This stuff is really cool and relates mostly to Stark’s Law (not Tony a.k.a Iron Man). The law incorporates hydrostatic pressure and oncotic pressure. Hydrostatic pressure is caused when fluid exerts pressure on the walls of the lumen of a vessel. This pressure wants to push fluid from within the vessel through the walls causing leakage. The higher the pressure the more leakage you will likely have. Oncotic pressure refers to pressure exerted on fluid to balance out an osmotic gradient (i.e. more stuff in one compartment than the other). The more stuff you have in one compartment the more water wants to “dilute” the substance driving water to the side with the most amount of stuff. There are proteins in your blood that want to drive fluid into the lumen of the vessel to balance out the protein in the blood. So, in general, hydrostatic pressure pushes fluid out of your vessels and oncotic pressure counterbalances drawing fluid into the vessel. These forces will reach an equilibrium. Basically too high of pressure in the blood vessels (hypertension) and too low of oncotic pressure (malnutrition) can cause fluid to leave the blood vessels.
Well that was kind of boring. Let’s get to the images. If fluid leaks out of the pulmonary vessels, it can be visualized on chest X-ray. Personally, I like to break the phenomenon down into three discrete and identifiable entities that I feel have a correlative physiologic process. These processes will often occur along a continuum if not corrected. I describe these process in my X-ray reports as pulmonary vascular congestion, pulmonary interstitial edema, and pulmonary alveolar edema.
PULMONARY VASCULAR CONGESTION
Here the hilar vessels lose their nice circumscribed margins, which become hazy and ill-defined. This is often a minor finding and can be over called in chest X-rays with low lung volumes or portable technique. I like to look at the vessels to the right of the carina. Here when looking down the barrel of the vessel/en face, the vessels look circular and can be pretty much outlined with a pencil line, like above. But when engorged they become less distinct and fuzzy, like below.
PULMONARY INTERSTITIAL EDEMA
Here, the findings should not be a diagnostic dilemma. The hydrostatic forces exceed the oncotic forces and fluid is pushed outside the cells and backs up into the space between cells called the interstitium. When this happens the intercellular markings are increased and can form these lace-like opacities or thin lines at the periphery of the lung called Kerley B lines (yeah, let me know if there is anything stupid left to put my name on). Additionally, the lungs have a gradient with more blood vessels near your feet than head. When pulmonary blood pressure goes up, the vessels at the top of the lungs eventually become engorged with fluid, called cephalization of the pulmonary vasculature.
PULMONARY ALVEOLAR EDEMA
This is when things are getting dire. Fluid has now filled up the interstitium and are backing up back into the air cells. This eliminates the possibility for air exchange and patients are pretty much drowning in their own fluids. When this happens the fluid fills the airspaces and patchy opacities may be present at the bases, with or without pleural effusions.
So that’s it. A brief tour of pulmonary fluid overload. I’m going to try and break into vlogging and see how it goes. So…. stay tuned for FLUORO!!!