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Pulse Oximetry (Nursing)

by Rhonda Lawes

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    00:01 Hi, welcome to our respiratory system video series.

    00:04 Now, in this one, I'm gonna breakdown what a pulse oximetry and capnography is.

    00:09 Now, listen, that is way cooler than it sounds.

    00:12 If you understand how these work, these become powerful tools in taking the best care of your patients.

    00:19 So, you're probably already familiar with this.

    00:21 This is just one example but what are pulse oximeters used for? Well, conventional pulse oximeters diagnose hypoxia.

    00:30 That means low oxygen in the bloodstream.

    00:32 Now, some pulse oximeters can also look at other parameters like methemoglobin and carboxyhemoglobin levels, that's really cool. We'll touch on those a little bit later.

    00:43 They can also look at total hemoglobin and even oxygen levels above 100% saturation.

    00:48 These are not likely the pulse ox's you're gonna be exposed to in most settings.

    00:53 So, we're gonna talk first of just the regular old generic, conventional pulse oximeter.

    00:59 They actually can do some pretty cool things. So, you've got a pulse ox. It's a small sensor.

    01:06 Usually, we put it on the end of an adult's finger and it'll help us measure how much of the hemoglobin in the blood is carrying oxygen or oxygen saturation.

    01:17 Remember, hemoglobin as adults, we have four of those carriers in each of our red blood cells.

    01:22 It combines with oxygen and the red blood cells carry that throughout our body.

    01:28 Now, normal ranges are around 96 to 100% if you're at sea level.

    01:34 Okay, so, that's what's considered normal for those of us that live at sea level.

    01:38 Now if you live high up in the mountains at a higher elevation, you might have a little bit lower oxygen saturation level.

    01:46 So, keep that in mind if you're practicing in a level or at an area in a hospital that has a higher elevation.

    01:53 It will be just a little bit different. Now, a little bit more about the normal ranges.

    01:57 Pulse ox's are usually calibrated to a range of saturation from 70 to 100%.

    02:03 Now, they're accurate with about two to four percent range.

    02:06 That may not seem like a lot but it can be a big difference, four percent in a patient's pulse ox rating.

    02:12 So, keep that in mind. Machines that measure things are just that.

    02:18 They're machines that give you a number. Your assessment of a patient is critical.

    02:23 So, compare what you're seeing with a patient live and in person and the numbers that you're getting to make sure you're making a strong correlation if that number is actually accurate. Now, if it's less than 70%, really, you need a blood gas.

    02:39 You can't make very many decisions based on a pulse ox that's less than 70%.

    02:43 It's just not calibrated to be that accurate.

    02:45 So, if you're really concerned about somebody's oxygenation, arterial blood gases are the gold standard.

    02:53 That's gonna be actually way more accurate than a pulse oximetry reading.

    02:58 Okay, so, when we talk about pulse ox, we're talking about the SaO2.

    03:03 So, oxygen in your body combines with hemoglobin and it forms oxyhemoglobin.

    03:09 Okay, before we go forward, I want you just to kind of soak that up.

    03:14 I've got a great picture for you there. You see the red blood cell.

    03:18 It's kind of like disk shaped or it's got an indentation in the middle. They call that biconcave.

    03:24 That's what a red blood cell looks like. It's just this empty sack doesn't have a nucleus and it's got those oxygen carriers we call hemoglobin.

    03:34 Now, when oxygen attaches or combines with hemoglobin, we call it oxyhemoglobin.

    03:41 I want you to keep in mind, that's a good thing. Oxyhemoglobin is what we're after.

    03:48 So, underline that word, circle it, and get it set in your mind that that's the good.

    03:54 Oxyhemoglobin is good. Because we're gonna talk about a lot of words that also have hemoglobin but what they're carrying is not oxygen.

    04:03 When a pulse ox uses some specific waveforms of light and it will compare the level of oxyhemoglobin to, right, take a look at that word, deoxyhemoglobin.

    04:14 That means hemoglobin that hasn't combined with oxygen.

    04:19 So, what I'm looking for is oxyhemoglobin. That means it's connected.

    04:24 Deoxyhemoglobin means it doesn't have oxygen, so, it's not really beneficial to us.

    04:30 Now, you look at the pulse ox.

    04:32 We've given you a drawing here where you see I have three, six, nine, 12 of these to look at.

    04:39 Now, 75% of them or nine out of 12 are carrying oxygen.

    04:46 So, the sat is the ratio of the oxyhemoglobin, the good ones, the ones that are carrying oxygen to deoxyhemoglobin, the ones that aren't carrying oxygen.

    04:58 That's why in this drawing, we've given you nine red ones to make it look like, yes, these are the ones that are oxyhemoglobin because they're carrying oxygen.

    05:05 The three blue ones or the 25% are deoxy and we've colored them a bluish color for you to help your brain remember those are the ones that are not carrying oxygen.

    05:17 Now, what's the benefit of a pulse ox over an ABG? Well, an ABG takes one measurement at the exact time that you'd withdraw that sample, it tells you what was going on in the body.

    05:28 Now, it is very accurate but a pulse ox is more indirect measure but we can get one continuously.

    05:36 So, they both have their place in health care.

    05:39 Now, let's try a question. What's the difference between ventilation and oxygenation? Really, this does matter and it'll come into play throughout our study of the respiratory system.

    05:52 So, stop and think, what's the difference between those two words, ventilation and oxygenation? Pause the video, write yourself some quick notes, then come back, we'll talk about the answer.

    06:11 Okay, welcome back. They did a great job on the graphic here.

    06:15 Look at this. Ventilation is the air movement in and out of the lungs.

    06:20 So, we've kind of got that bluish grey color there but on the other side, they give you the definition of oxygenation because that's the amount of oxygen inhaled by the lungs that reaches the blood stream.

    06:33 So, ventilation is the movement of the air.

    06:37 Oxygenation is the amount of oxygen that actually makes it to the bloodstream that's been inhaled by the lungs. Both are important.

    06:45 You need air to be delivered but you also need it to get to that bloodstream so it can be delivered to the rest of the body.

    06:53 So, that's a difference between ventilation and oxygenation.

    06:56 So, when you hear us use those terms throughout the rest of the video series, keep that in mind, remember this picture.

    07:02 Ventilation, movement of air, oxygenation is the amount of oxygen that's inhaled by the lungs that actually makes it to the bloodstream.

    07:12 Okay, does the pulse oximeter measure ventilation or oxygenation? Okay, cool, this is a really good question. So, don't rush through. Pause and think about it.

    07:24 Go back to the definition that you know of ventilation and oxygenation, then, think about what we've talked about and give it your best educated guess.

    07:41 Welcome back, oxygenation because it measures how much of the each red blood cells hemoglobin is bound to oxygen.

    07:50 So, that's why it's not ventilation. It doesn't tell us how much air is moving in and out of the lungs.

    07:55 A pulse ox uses those special wave forms to identify how much of the red blood cells hemoglobin is bound to oxygen.

    08:05 Now, there are some special cases where hemoglobin can bind to something else.

    08:09 We'll talk about that later but as we're just beginning this concept, I want you to keep in mind, pulse ox measures how much of each red blood cells hemoglobin is bound to oxygen. Okay, now, we've got a picture for you there.

    08:23 The pulse oximetry uses two lights to analyze hemoglobin.

    08:27 So, that's why it's on the top and the bottom of the patient's finger.

    08:32 Now, looking at that drawing that we have for you, you see there's arteries in red, veins are in blue.

    08:38 We've got that light emitting right on the top then, there's a photodetector on the bottom.

    08:44 So, it clips over the finger, we have a light and then, a receiver.

    08:49 Now, the red light has a wavelength of approximately 650.

    08:53 That's not information you need to store in your brain.

    08:56 We're just letting you know and an infrared light has a wavelength of 950.

    09:00 So, we've got red light with one wavelength. We've got infrared light with another wavelength.

    09:07 That's all you need to remember about the pulse ox.

    09:10 Don't worry about remembering the actual specific measurements.

    09:13 Okay, now, we're not asking you to be able to recreate a pulse oximetry but I want you just to understand how it works because when you understand how things work, it's gonna help you make more sense of the clinical information you're collecting about your patient.

    09:26 So, we've got two red cells here, right? We've got oxyhemoglobin and deoxyhemoglobin.

    09:34 Well, remember, which one indicates it's combined with oxygen? Right, oxyhemoglobin.

    09:41 Now, in the instance of oxyhemoglobin, when these different lights, infrared and red light are passed through your finger, there's gonna be more infrared light absorbed in red light if it's oxyhemoglobin.

    09:55 On the deoxyhemoglobin, when those lights pass through your finger, there's gonna be more red light absorbed than infrared light for the deoxyhemoglobin.

    10:06 So, don't worry about trying to keep those straight. Just keep in mind, a pulse ox uses two forms of light, different waveforms, oxyhemoglobin and deoxyhemoglobin, absorb them at different rates.

    10:19 That's how we can come up with a percentage.

    10:22 Because the pulse oximeter works out the oxygen saturation by comparing how much red light and how much infrared light is absorbed by the blood.

    10:30 That's the piece you want to remember.

    10:33 It takes a look at comparing how much red light and how much infrared light is absorbed by the blood.

    10:39 Since we know oxyhemoglobin and deoxyhemoglobin absorb these differently, they could come up with a pretty good estimate of saturation.


    About the Lecture

    The lecture Pulse Oximetry (Nursing) by Rhonda Lawes is from the course Respiratory Assessment (Nursing).


    Included Quiz Questions

    1. Hemoglobin in the blood (oxygen saturation)
    2. Potassium
    3. Internal temperature
    4. Respiratory rhythm
    1. 96–100%
    2. 90–100%
    3. 89–100%
    4. > 90% as long as 2 liters of O2 is applied
    1. Arterial blood gases (ABGs)
    2. Fraction of inspired oxygen (FiO2)
    3. Pulse oximetry (SaO2)
    4. End-tidal CO2 capnography
    1. Ventilation
    2. Oxygenation
    3. Perfusion
    4. Pulse oximeter reading
    1. Oxyhemoglobin
    2. Deoxyhemoglobin
    3. Arterial blood gases (ABGs)
    4. Fraction of inspired oxygen (FiO2)

    Author of lecture Pulse Oximetry (Nursing)

     Rhonda Lawes

    Rhonda Lawes


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