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V/Q Mismatch (Nursing)

by Rhonda Lawes

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    00:01 Now, this is a little different story. V/Q mismatch means something's wrong.

    00:07 Either it's the amount of air or it's the amount of blood. And so, we don't have good gas exchange.

    00:13 We need to figure out what is the problem. Is it the amount of air coming in or is it the blood? Now, I had a V/Q mismatch but that's because I had a pulmonary embolism.

    00:24 So, that's why my test results were off and this helped them identify that was the problem.

    00:30 But when we have a V/Q mismatch, it could be a problem in the amount of air or the blood flow.

    00:37 My case? It was the blood flow but it could be either one and that's how this test can be helpful.

    00:43 Because we know a normal V/Q ratio, now we're just coming and looking at it from a little bit different angle.

    00:49 This is a way to ease your brain into this concept as we walk through it.

    00:53 Wanna be very sure you know what normal is, then we're gonna look at what the problem is in high or low ratio.

    01:01 So, we've got V divided by Q, air divided by blood perfusion.

    01:04 Normally, it would be four divided by five, we get 0.8.

    01:08 That means I've got enough oxygen coming in. I've got the right amount of blood flowing by.

    01:12 Do you see what we've done for you in this graphic? We are very intentional about everything we show you on a slide.

    01:19 So, you're seeing the oxygen come in to the round part is the alveoli.

    01:23 Look at the blood flow, see, it's unoxygenated, it's blue, then you see it mixing at the alveoli and it leaves red to represent oxygenated. That's really cool.

    01:35 So, whenever you see a picture or a diagram, make sure you see if it makes sense to you.

    01:41 If it doesn't, that's a good clue and something you need to go back and study because everything is done with a purpose because we really wanna help you grasp these concepts.

    01:53 Now, this is just showing us, this is normal, again one more time, just to use repetition to help your brain remember.

    02:00 Four divided by five equals a normal V/Q ratio of 0.8. Now, look what's different in this slide.

    02:06 This was normal. Now, we're gonna look at, whoa, how would we get a high V/Q ratio? Well, the reason we call it a high V/Q ratio is because 1.33 is larger or greater than 0.8.

    02:22 If 0.8 is normal and you've got anything higher or larger than 0.8, we call that a high V/Q ratio.

    02:29 So, what would have to happen in order for us to get a higher V/Q ratio? Is that the capillary blood supply would be less. For some reason, it's impaired.

    02:41 So, air is still coming in but there's a problem with blood supply.

    02:46 That's why instead of a five, we just randomly picked a three for you.

    02:51 To illustrate when you have a high V/Q ratio, what's the problem? Blood supply.

    02:57 So, pause the video for just a second, see if that makes sense to you.

    03:01 Pretend you're trying to explain it to a fellow student, why does a high V/Q ratio mean impaired blood supply? Okay, good. I hope this is making sense to you as we're walking through it because with a high V/Q ratio, where those numbers are adjusted a little bit, we've got a problem.

    03:26 One example is like what I had, a pulmonary embolism. So, look at the graphic.

    03:32 You've got oxygen coming in the bronchiole to the alveoli, right? We've got plenty of oxygen in there but we've got a problem with a PE.

    03:40 So, we have enough oxygen coming in, that's why it was normal at 4 but anything that causes impairment in the blood supply and PE is just one example, then it's gonna be less than 5.

    03:54 Your V/Q ratio by the basic rules of math is just going to be higher.

    04:00 So, if you have a patient and they have a high V/Q ratio, that means there's some problem with the blood supply, not the ventilation, but the perfusion is the problem.

    04:13 So, watching those signs can tell you a lot about what's going on in your patients.

    04:18 If the perfusion is severely compromised or blocked completely, it's really gonna be a different result.

    04:24 So, you can see, might be a PE but some other examples to consider would be an extremely decreased cardiac output, right? So, that heart really not able to pump, then that perfusion's gonna be significantly decreased, that's gonna be a problem or completely blocked by a pulmonary embolism.

    04:45 So, a high V/Q ratio, the cause has to be something has impaired the supply of blood to the capillaries, so, it's gonna be less than five which gives us a V/Q ratio that is greater than normal or higher than 0.8.

    05:01 Now, let's look at the opposite. Blood supply's going fine.

    05:05 You've got a rate of five liters, that's what we would expect but something is impacting the alveoli receiving air. So, it's less than four.

    05:15 Now, the V/Q ratio is going to be less than 0.8 or a low V/Q ratio.

    05:22 So, let's try an example. Let's make it 3.

    05:25 Let's say that the alveoli receiving air at 3 liters a minute.

    05:29 Now, when you do the math, 3 divided by 5 equals 0.6. 0.6 is less than 0.8.

    05:38 So, that's why we call it a low V/Q ratio. Is there any problem with the capillary blood supply? No. The problem is with the supply of alveoli receiving air.

    05:51 So, a low V/Q ratio and we used the same ratio we use for every one of these figures, you've got impaired less than 4 liters a minute divided by 5.

    06:02 So, for some reason, the patient is not able to be receiving air effectively.

    06:07 The ventilation is compromised.

    06:09 So, a portion of the blood is not getting oxygenated because you're not getting enough of the oxygen in.

    06:16 Now, what are some examples? It could be someone who's just having difficulty with maybe opioid overdose like we've talked about or they can't catch their breath, they're over sedated.

    06:26 Any reason that can cause a patient to not be able to take air in is gonna cause a lower V/Q ratio.

    06:36 Now, this one is extreme. When you look at this, look, you've got blockages on both ends.

    06:41 You've got air not coming in, you've got blood not going by. This patient is dead.

    06:46 We call it a V/Q ratio of a silent unit.

    06:48 It might be something as life threatening as a pneumothorax where you've got air in that cavity and so everything is just collapsed or an advanced form of respiratory problems with acute respiratory distress syndrome. This is clearly life threatening if you can't figure out what the underlying cause is and resolve it.

    07:09 This patient is extremely critical. I wanna introduce you to the topic of shunting.

    07:17 Now, shunting and we're talking about blood, it causes unoxygenated blood from the right side of the heart to move through to the left side of the heart.

    07:26 Okay, well, why is that such a big deal? Once the blood gets to the left side of the heart, where's it gonna go? Left side of the heart, the atrium, the ventricle, oh, out to the rest of the body, so, that's not good. We need the blood to go from the right side of the heart to the lungs to get oxygenated before it comes back to the left side of the heart.

    07:50 So, we've got some shunting and it might be some different reasons that cause it but shunting is essentially unoxygenated blood going out to the rest of the body, not a good deal for my cells. So, what are some possible causes? Well, you might just have a physical defect.

    08:07 That allows the unoxygenated blood to pass through to the alveoli, not good.

    08:13 So, there might be some defect that allows blood that's not been oxygenated well to make it to the alveoli.

    08:19 Also, you could have an airway obstruction.

    08:21 That could prevent oxygen from getting to an area of the lung, too.

    08:24 So, if we have oxygen that's not getting to the lungs, unoxygenated blood is going to get to the rest of the body.


    About the Lecture

    The lecture V/Q Mismatch (Nursing) by Rhonda Lawes is from the course Respiratory Assessment (Nursing).


    Included Quiz Questions

    1. The gas exchange is impaired by an issue with air or blood.
    2. Type and screen for blood do not match the donor.
    3. The blood is too deoxygenized to perfuse skin tissue.
    4. The ventilation and perfusion exchange are functioning efficiently together.
    1. Alveoli receive air at 4 L/min.
    2. Capillaries supply blood at 5 L/min.
    3. V/Q ratio is calculated by the air (ventilation) divided by the blood supply (perfusion).
    4. Alveoli receive air at 5 L/min.
    5. Capillaries supply blood at 4 L/min.
    1. Narrowed capillaries or dead space such as a pulmonary embolus
    2. Heavy carbon monoxide exposure
    3. Presence of acute respiratory distress syndrome (ARDS) and treatment with 2 liters of oxygen administration via nasal cannula
    4. Opioid overdose
    1. Shunting
    2. Acute respiratory distress syndrome (ARDS)
    3. V/Q mismatch
    4. Airway obstruction

    Author of lecture V/Q Mismatch (Nursing)

     Rhonda Lawes

    Rhonda Lawes


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