Airway disease versus alveolar disease
Before you can fine-tune your patient's ventilation settings, you need to know whether they're suffering from an airway disease or alveolar disease.
Before you can fine-tune your patient's ventilation settings, you need to know whether they're suffering from an airway disease or alveolar disease. In this video from our Mechanical Ventilation Essentials course, you'll look at the general characteristics of each category of disease, how each disease manifests in the body, and clues that will help you determine which category your patient falls into.
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[00:00:00] Now that we've covered the basics, it's time to go a step further in developing skills to refine our ventilation settings for the patient. Now, before we do, we need to determine which general lung disease category the patient falls under, once they are mechanically ventilated: airway disease or alveolar disease. So, let's look at several characteristics of these two general lung disease categories and we'll begin by observing some basic characteristics of airway disease and then we'll compare that with the characteristics of
[00:00:30] alveolar disease. Understanding these characteristics will lay the foundation for how to refine our initial ventilator settings. So first, the airway disease patient. Now, when we refer to airway disease, we're simply referring to the physical airways that carry volume in and out of the lungs. Normal airways should be patent and allowing for adequate flow of volume. The inside of a normal airway should look something like this, wide open and patent.
[00:01:00] But in a patient with airway disease, the inside opening of the airway becomes narrow. This can be caused by inflammation inside the airway, which reduces the opening diameter or mucus in the airway, which also reduces the opening diameter of the airway or even if the patient has asthma or the smooth muscles that wrap around the physical airways can constrict and squeeze the airway opening, so that it also becomes more narrow. Now, the general description used to classify these types
[00:01:30] of airway diseases is obstruction. That's because the opening of the airway is obstructed or narrow, due to inflammation or mucus or smooth muscle airway bronchoconstriction. So, what's the main challenge with these types of patients? Well, with these patients, getting volume into the lungs isn't necessarily the main challenge. A patient with an obstructive airway disease should still be able to inhale an adequate amount of volume. Now, think about that, if you switched from inhaling
[00:02:00] through a large bore straw to a narrow bore straw, you would still be able to inhale the same amount of volume but you wouldn't be able to inhale as fast. So, it's important to know that the main issue isn't necessarily getting adequate volume in. The main issue is getting the volume out of the lungs. So, watch, try this experiment. Go ahead and mimic exhaling through an obstructed airway. Let's obstruct our mouth by pursing our lips. Now,
[00:02:30] go ahead and take a deep breath in and then exhale. You should notice that getting the volume in is not that difficult, however, exhaling all the volume takes a lot of time. Now, depending on how much you purse your lips, you can actually exhale for up to 20 seconds. So, airway disease patients will actually be at risk of air trapping. This is where accumulated volume, over a long period of time, actually stays trapped in the lung. This also
[00:03:00] means that CO2 is not properly being ventilated out, since some of the volume which is supposed to carry out the CO2 is being trapped. So, look for these types of patients to have higher than normal levels of CO2. Also, on an x-ray, the lung size might actually appear larger since, over time, there is an accumulation of volume. So, in general, patients who have an airway disease, exhibited by a decrease of air flowing in and out of the lungs, will be at risk of air trapping and
[00:03:30] increased levels of CO2. Now, in the upcoming videos, we'll discuss strategies to identify and modify ventilator settings to treat patients with airway disease. Next, is alveolar disease. By alveoli, we simply refer to the non-airway part of the lung. There are over 300 million alveoli in the lungs. So, if you can't see it in this drawing, with the naked eye, it's because well, you can't. They're microscopic. But let me show you a cartoon of what one little alveolus is as well as
[00:04:00] its purpose. Here, is one magnified alveolus. Again, notice that this is not an airway. This is where air terminates into. In other words, as air is inhaled through the airways, air eventually ends up going into the alveoli, which are tiny little air sacs. From the alveolus, the oxygen can diffuse into the pulmonary bloodstream and this is where blood becomes richly oxygenated. But if the alveoli is damaged, it can collapse on itself. This leads to the inability to adequately
[00:04:30] inflate the lung and if we can't get adequate volume in, then we'll have a difficult time getting oxygen to the patient's bloodstream and their body. So, depending on the severity and extent of the alveolar damage, patients with this disease will have a difficult time getting adequate volume of air into the lungs, which in turn will lead to decreased oxygenation and on an x-ray, the lung may actually appear smaller in size. In severe cases, alveolar lung
[00:05:00] disease can lead to ARDS but we'll talk more about this later. For now, let's recap and do a quick side by side comparison of the two general categories of lung disease. In an airway disease, the speed of air flowing in and out is decreased. With alveolar disease, it's not an airway issue, it's a matter of collapsed alveoli not able to open to receive volume, therefore, the volume entering the lung will be decreased. In airway disease, the patient will have difficulty getting volume out,
[00:05:30] which in turn leads to air being trapped in the alveoli. In alveolar disease, the patient will have difficulty getting volume in, due to collapsed alveoli. In airway disease, because the patient will have difficulty getting volume out, this will lead to increased PaCO2 levels since CO2 is not properly being ventilated out. In alveolar disease, because the patient suffers from alveolar damage, this will lead to decreased PaO2 levels.
[00:06:00] In airway disease, because the patient is not ventilating CO2 out, this disease category is said to have a ventilation issue. But in alveolar disease, because oxygen cannot enter the collapsed alveoli, this disease category is said to have an oxygenation issue. On an x-ray, the airway disease patient usually has larger looking lungs because of air trapped over time. On the other side, the lung appears to shrink in size so the chest x-ray will appear smaller. This side is
[00:06:30] referred to as the obstructive disease, while this side is referred to as the restrictive disease.