The “I” in HORID stands for infection – meaning pneumonia. When thinking about pneumonia, you want to look at both clinical features and use pretest probability to look for leukocytosis, respiratory rate and O2 Saturation. The diagnosis hinges on the CXR.
Young, healthy people come in and tell you what they have by their symptoms: coughing terribly, high fever, bringing up gooky yellow/green sputum. In cases like this, pneumonia is a relatively easy diagnosis. But in children and elderly folks, pneumonia may present in much more subtle ways.
Examining the Types of Pneumonia
Once again, 9 out of 10 times, if someone comes in and you are very concerned about a bacterial infection, think wind and water, meaning pneumonia or urinary tract infection.
Radiographically, there are three different presentations of pneumonia. We have bronchial pneumonia, alveolar pneumonia and interstitial pneumonia. All of these pneumonias are noted by where the pneumonia sits anatomically. Does it sit in the bronchial? Does it sit in at the end of the bronchia in the alveolar area? Or, does it weep out through the alveolar area into the interstitial area?
If the bronchial gets completely occluded, that can decrease the pressure going to the alveolar area. I like to think of the alveolar area as a big bunch of grapes where as you breathe in, the grapes expand, and as you blow out, the grapes shrink to kind of look like raisins. If someone has a bronchial obstruction, we would not have enough pressure to keep those grapes enlarged, so they would all collapse – basically, that is another term for pneumonia.
What I would suggest in a bronchial pneumonia is that these germs are so big, they are like the size of PEAs and block up the bronchial. PEAs, or pseudomonas, E-coli, and anaerobes (which can happen in aspiration pneumonia. Here is where we would put a big flag up for klebsiella, which is classic with alcoholics) and staph.
The bronchial pneumonia is more of a hospital-acquired and health care-acquired picture such as the elderly lady who came to the hospital for hip surgery. She was doing quite well, but then on day three came up with fever, white count, hypoxia and a big infiltrate. In those people, we would want to be quite aggressive in treating for pseudomonas. Now, alveolar pneumonia has to do with an infection down in the hand or in the grapes area. My pneumonic there is SHZAM. S is strep pneumo. H is haemophilus influenzae. Z is just to fill in the pneumonic. A stands for atypicals. M is for moraxella catarrhalis. This is your classic community-acquired pneumonia. This is someone who comes in off the street with fever, cough and x-ray that shows pneumonia. For patients who come in with community-acquired pneumonia, we need to treat them for the different classes of germs. So, we have to treat for gram positives, gram negatives and atypicals. The most common way to treat them is either with a macrolide antibiotic (non-erythromycin because erythromycin does not cover gram negatives), fluoroquinolone antibiotic (ciprofloxacin does not cover strep pneumo well), or combination therapy of something like a third generation cephalosporin and a macrolide.
Alveolar pneumonia predisposes patients to air bronchograms. If you have an infection that sets in there, you will have pus and gooky stuff that weeps upstream, not back up the bronchial, it cannot go back up the bronchial, but would weep around the arm. So, because you have an area that is opacified, you will have a black linear density which is air that is still in the bronchial, this is referred to as an air bronchogram. So we do see air bronchograms with alveolar pneumonia as well as congestive heart failure, in any pathology where there is an excessive amount of fluid at the alveolar area.
Finally, let’s take a look at interstitial pneumonias. These are pneumonias that are so small, the germs are so small, that they do not get stuck in the bronchials, they do not get stuck in the alveolar area, they weep out into the interstitial area. This is typically the types of viruses, called a pneumocystis jirovecii pneumonia, that are seen in HIV patients. These patients typically have a diffuse pattern that I have heard described as white chicken fence on a black background. To me it looks like someone decided to paint the lungs using a very coarse paintbrush and is painting in all sorts of different directions with no pattern to it. Now, this interstitial pattern can also be the presenting appearance of an interstitial pathology such as pulmonary fibrosis or asbestosis where the patient has more of a chronic pattern. Clinically, when you listen to these patients’ lungs, they will have very coarse rales in their lungs. I have never had a patient present with an interstitial lung disease and not know it, not being followed by a pulmonologist. They will make you well aware of that.
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