Vital Signs are Vital: SpO2

(upbeat music) - Welcome to the Critical Care Obstetrics Podcast. I'm Stephanie Martin, Medical Director at Clinical Concepts in Obstetrics, and I'm here today with my partner, Suzanne McMurtry-Baird, Nursing Director at Clinical Concepts in Obstetrics. Today, we're following up on our series on vital signs are vital. We've already covered three vital signs, heart rate, blood pressure, and the ever-missing respiratory rate. And today, we're gonna continue our conversation about the lungs and respiration and expand it to oxygenation and focus on the oxygen saturation. So hopefully, you guys are learning a lot from this, but if you wanna learn more about high-risk and critical care obstetrics, you should check out our Critical Care OB Academy that's available online at our website, clinicalconceptsinob.com. And I wanna also highlight that we've been getting a lot of requests for group pricing. Maybe you wanna explore if many nurses on your unit can take it or you're in a residency training program and you wanna have your residency class take it. We are more than happy to provide group pricing, so please reach out through the website. And we'd love to hear more feedback about what you guys think about the online Critical Care OB Academy. So let's dig into oxygen saturation. As always, before we get into details about the oxygen saturation, we wanna highlight a few key points about vital signs in general. These are crucial points to remember. You've heard me say before that if you wanna annoy me, call me with one vital sign. I wanna know all the vital signs, so please do a full recording of the vital signs. A single vital sign measurement really is not very good at predicting adverse events. You need combinations, the pulse plus the heart rate, the pulse plus the blood pressure, plus the respiratory rate, et cetera. And these combinations really improve your ability to understand what's happening and predict whether bad things are on the way. The more you understand vital signs, the more uncomfortable you will be with a single vital sign, and the more uncomfortable you will be when you identify one as abnormal. It's really also not just about a single vital sign, more than just the combinations, but also trends over time. Like what's actually happening with your patient? - Yeah, I was thinking about that, Stephanie, when we were talking in the last episode about the early warning criteria, many of the algorithms and the early warning criteria are combinations of vital signs. So it's not just one standalone and they need to be sustained. So obviously you don't wanna watch for too long of a period of time, but let's say you do a pulse oximetry and you're watching that trend, or you take a respiratory rate and it's too high, then where has that patient been? So it's a combination of those two or something else in combination to look at that early warning criteria. - Absolutely. It's so, so important to understand what's happening with those vital signs, and you really can't understand that with a single vital sign that's not repeated over time and in isolation without combining it with other things. So before we talk about hypoxemia and oxygen saturation in general, I wanna talk about the equipment. So I'm gonna keep it real simple. I go into it in a lot more detail in the academy, but very, very simply, when you put a pulse oximeter on someone's finger or their earlobe or their toe or whatever, you're essentially shining red light through the tissue. And the computers are calculating how much light is absorbed and that gets translated into how red the blood is in very basic terms, how red is the blood. And the redder the blood, the more saturated hemoglobin is with oxygen molecules. So it's very simply looking at, is the blood this red or less red? More red or less red? And the computers have done the calculations for you and they translate that to the percentage of hemoglobin that is saturated or carrying an oxygen molecule. So in order for the equipment to work, you have to have a good pulse. You've got to have blood flowing through the digit or through whatever. - Yes, that's such a good point. I remember you and I were in a room one time and we had this patient that was hemorrhaging and we had trained this team. We had trained them and the first thing I saw was a nurse coming out of the room during this emergency. And I said, "Where are you going?" He said, "Well, the pulse oximetry is not working." And I was like, palpator pulse, like hands on palpator pulse. And you could see the nurse palpating and not getting or really feeling a strong quality pulse or it being absent. And I thought, yep, yes, it's different hearing it in a classroom or on a podcast or in a lecture, but really in those clinical situations and you're not getting away from, it's not the equipment. It's the fact that this patient has hemorrhaged so much that she doesn't have a quality pulse and the quality is so weak that you're not getting able to get away from. So I just wanted to put that in place because even with all the training and us talking about it now, I want you to think about that the next time you have a patient that you're not getting away from on or you start to see it being dampened or intermittent readings, how pay their pulse 'cause I love pulse quality. - We love a strong pulse. - I love a strong pulse. - Always assume your equipment is working. I mean, think yourself, you've probably changed out the pulse oximeter attachment, the sticky pads, that portion of the device, countless times in your career, but did it ever really fix the problem? Was it ever really the problem? Okay, well, maybe if all the sticky was worn off and had been taken off a million times and it's not holding in place or whatever, but the reality is most of the time the equipment's working just fine and it's us who's not appreciating that that fingertip is not getting an adequate perfusion of blood because your patient is running out of blood. - Right. - Or she's in septic shock and the body doesn't think that the fingertip is an important part. It's gonna be perfusing kidneys and brain. So just assume your equipment's working, okay? - Right. And that's easy to shoot, you know, troubleshoot, you know? - Real easy. Just see if it's fixing, you know, if it's attached well where it needs to be and check their pulses. So let's talk about hypoxemia. Now, commonly we interchange hypoxemia and hypoxia. They are actually not the same thing. I'm sure I have misspoken on many an occasion, but hypoxemia is low oxygen level in the blood. If left unchecked and uncorrected, it will ultimately lead to hypoxia, which is low oxygen levels in the tissues. And that's what we're trying to avoid by intervening early. We wanna correct the amount of oxygen in the blood so that we can improve the likelihood we're gonna have good amount of oxygen in the tissues. So hypoxemia in obstetrics is defined as a hemoglobin saturation or an oxygen saturation, pulse ox, O2 sat, whatever you wanna call it, of less than 95%. In a pregnant patient, your pulse ox should be, your oxygen saturation should be 95% or greater. And it's important to understand, like we've been highlighting, we're not looking at these values in isolation. You wanna see trends over time. It's not unusual to have a patient sat, drop down, all of a sudden it's 88, 89 while she's eating lunch. And then as soon as she holds her hand still, you get it attached well, you make sure you've got a good connection. We're back in the 99 to 100 that she's been all day long. So a single value is really not useful in isolation. You need to be looking over time. - Yeah, and that's, I remember that came up, oh, it comes up at the bedside all the time. I remember having a nursing student with me one time and said, her pulse oximeter value keeps jumping down. And then it goes back to normal and it jumps down and goes back to normal. I said, because she's moving and you're getting an erroneous value in there. Which I think is also important to bring up because again, those values come over to your machine. So if you have like a little disconnect in your pulse oximeter sticky that we talked about earlier, or if she's moving a lot, then you're gonna get some erroneous values and they automatically go over into your documentation. You need to state something like, you know, obviously if her pulse oximeter value was, you know, 78 truly, then she would be in a crisis, right? So, and then it's gonna come right back up to 98%. That's not the way this technology works, right? So oxygen doesn't hop on to hemoglobin and hop off that fast and then reload immediately. So there's some kind of issue if she were to sustain a pulse oximetry value around 78. But to have an erroneous value here and there, that's just movement. - Now the other, like the opposite of this where some of these values might actually be real and critical. So what we're describing are erroneous measurements, which are just quality of your measurement typically, okay? And you guys can tell that easily. You all know it when it happens. You see it, it jumps down and comes right back up with just some little fiddling or whatever. But if you have a truly critically ill patient, they might be on the edge and they might not have a lot of oxygen dissolved in their blood. And so just rolling them over in the bed or turning them on their side will cause them to desaturate. And that is a consumption issue and an oxygen delivery issue in a critically ill patient. We talk a ton more about this in the Academy. But again, it's not gonna go down in a blink and come back up in a blink. You'll see it go down and then come back up as they get back into a resting position and their demand and their consumption goes down and their delivery improves. So there are times where those changes are actually real and important, but that's where your trends and your combination with other vital signs will help you understand what's happening. So let's talk about what the saturation actually means. So when we say oxygen saturation, the other way to think of it is hemoglobin saturation because each hemoglobin molecule can carry a fixed amount of oxygen. So hemoglobin as a molecule can carry a certain amount of oxygen and it can't carry any more than that. You can't overload it. It's gonna carry as much as it can and that's 100% saturated. Then as it delivers oxygen to your tissues, it releases the oxygen molecule and then it is less saturated than it was before. So if you look at venous blood, 'cause everything we're talking about right now is arterial, if you look at venous blood, it's not unusual for it to be in the 70s and 80s. That's what you want it to be because that means that oxygen has been delivered to tissues and it's ready to be reloaded again. So the saturation tells you is the hemoglobin molecule holding as much as it can hold. And that's what that 95% or greater tells you. No one is 100% all the time. That's just not realistic. We just want you to be good enough, 95% or greater. Now in the non-obstetric population, those of you who work in ICU's and med surge floors, you have a different threshold for quote, okay, and that's 92% or above. And the big difference is the fetus because the fetus has to have oxygen delivered as well. And if you are on the, so remember your oxy hemoglobin dissociation curve where you've got the balance between how much oxygen is in the blood and how much oxygen is on your hemoglobin molecules, the lower your saturation gets, then the more rapidly your patient is going to deteriorate clinically and have a rapid drop in their oxygen saturations. So you don't want them living on that cliff if they've got a baby that they've also got to support. Plus pregnant women have a much higher metabolic need, et cetera, than other patients. So we set a threshold of 95 and above. If they're not pregnant, we generally will accept a saturation of 92 and above. - Yeah, I want to highlight that a little bit, 'cause when we go into hospitals, sometimes that is in the physician orders for obstetrics as well as highlighted as abnormal, not highlighted, in other words, at that particular hospital until it reaches 92%. And when we have a patient that reaches 92%, that means their PAO2 is much lower at that particular point in time. And it's like you said, they're on that cliff and they're ready to dive off. And you'll start seeing fetal changes, which is the only evidence that we have that shows that oxygen improves fetal outcomes is when maternal PAO2 is low and we are trying to increase the PAO2 as well as increase their oxygen content as well as their oxygen delivery. So, and that's the rationale for MASCO2 in a pregnant woman. And the only evidence that we have that it's beneficial to the fetus is when mom's saturation drops or when her PAO2 drops. So just to highlight on that, because I know that that topic comes up, which will probably be another podcast in the future because lots of evidence keeps coming out and a lot of controversy over that topic. - So, couldn't agree more. Let's talk about PAO2 real quick or PAO2, same thing. So the saturation is how much oxygen that the hemoglobin itself is carrying. The PAO2 or the PAO2 is all the leftover oxygen that gets delivered to the bloodstream. Once the hemoglobin can't carry anymore, it's 100% saturated, all the extra gets dissolved in the blood. Okay, just think of it as a highly carbonated drink. The more oxygen you put in, the more gets dissolved in the blood. And so it's just sitting there ready to fill hemoglobin as it delivers oxygen. So when you have a decrease in your oxygen saturations, when you have high poxemia, that essentially means that she does not have enough oxygen dissolved in the blood to keep hemoglobin full. That is abnormal. You should always be able to fill the hemoglobin tank and just load it up with oxygen to its maximum capacity. You're not gonna have a high level of oxygen dissolved in the blood and a low oxygen saturation in a normal situation. The exception to that is carbon monoxide poisoning. But we're talking about a normal situation. You're not gonna have low saturations and high PO2s. Your PO2, your dissolved oxygen is gonna get all used up in order to keep the hemoglobin fully saturated. - That's the reason why we don't draw a lot of arterial blood gases anymore. We used to draw a lot more than we do now with the technology and the understanding of post-oxymetry. And so unless you have a patient on a ventilator or an acute compromise, you may or may not do an arterial blood gas, at least not at the frequency that we used to. - Yeah, the gases are super, super helpful when you're giving the patients getting a lot of oxygen and you don't know how much is getting in. So that's 'cause you can saturate your hemoglobin, but how much is actually getting through and dissolving in the blood? So we don't just routinely do them just because they have a low sat. If they've got a low sat, I know what their PO2 is. But when I'm giving 'em, let's say they're intubated, they're on 100% oxygen and their sats are 96, 97, I have no idea how much oxygen is dissolved in the blood until I check it. And so there's a role for it, but I totally agree. We're not just doing ABGs left and right just because we wanna know the PO2. I can guess it. - Yeah, I remember, I practiced at a time when we didn't have post-oxymetry. And I think that again, understanding the technology and what it even means is so helpful because if we were never really taught that when it first came out, we were taught, hey, put this on their finger or their ear. And I remember the little rubber things that fit on the finger that everybody used, which kinda grosses me out when I think about it now. But yeah, but we didn't really understand the technology. And I don't think that we've really taught it to all the clinicians that utilize this technology on what it even means. So I hope this has been being helpful to understand some of the ins and outs. - So now let's dig into the why because we think it's crucial that you understand the why. So causes, why does somebody have a decreased oxygen saturation? Well, first of all, if you're practicing at altitude, like I did for eight years of my career, when you're breathing in lower amounts of oxygen, you're gonna have lower amounts of oxygen in your blood. And there's no exception during pregnancy. So the higher altitude you are, then the lower amount of oxygen you're breathing in, but those patients should still be able to get their saturations up to 100%. They just might live at a little bit lower level. But generally speaking, they're adapted and everyone does well. I'm not gonna talk about high altitude medicine at this point, but you breathe in less oxygen, you're gonna have lower levels of oxygen in your blood. - I feel it when I go to Colorado. - That's why they sell the oxygen in cans and you put the little can over your face and just breathe it in and yeah. - You go to those little oxygen bars or something, you know? - Yes, they flavor it. - They can, yeah, I know, I've seen flavors. - So if you're paying for extra oxygen at the oxygen bar and you're in Las Vegas at sea level, all you're doing is raising your PO2, you're not doing anything else. - I've done that, have you done it? Were you with me or did you do that with me? - No, I didn't do it. - Okay, I did it. - But I was there. What happens in Vegas stays in Vegas. Who's Anne, stop talking. - Oh yeah, that's right, that's right, I'm sorry. I'm really being distracting today. - So otherwise, understand the why. So respiratory compromise, this is the number one thing that we are worried about. It's usually the reason we're monitoring our patients. We wanna know what's happening with their respiratory system. Are they compromised? Are they oxygenating well? And in a pregnant patient, when you have a patient who's hypoxemic, you're really talking about one of four things, the overwhelming majority of the time. And that's pulmonary edema, that can be cardiogenic or non-cardiogenic, that's a different podcast. And we talk about all of these things a ton in the academy. It can be asthma, asthma's just common, right? Pneumonia of any kind, community acquired, aspiration, COVID, whatever. And pulmonary embolism, a blood clot. Now they all cause decreases in oxygen levels for different reasons, but the final result is gonna be hypoxemia and then ultimately low PO2 levels if it's not corrected. So decreased oxygen in the air like at altitude, respiratory compromise. - And those are gonna present totally different too. So again, assessment goes along with this, not just a value of a pulse oximeter. - Yep. And then next is increased utilization. So when you're using a ton of oxygen, sometimes you just can't keep up. Like patients that are very febrile or septic or in septic shock, that might be a combination of pulmonary edema in conjunction with increased utilization because their metabolic rate is higher, they're fighting infection, whatever it may be. And so a lot of these things are in combination with each other. It's not just one issue that's causing it. And then the last one to think about is lack of perfusion like we talked about before. If you're not perfusing that tissue, you're gonna have a decreased pulse pressure, you're gonna have wave form issues, you may not be able to register the saturations. And the two most common scenarios where we'll see that in an obstetric population is gonna be sepsis and hypovolemic states like hemorrhage. So decreased inspired oxygen, respiratory compromised, increased utilization, lack of perfusion or a combination of all of the above. You can absolutely have a patient who's septic, who's not perfusing, who's got increased utilization and has non-cardiogenic pulmonary edema and maybe even pneumonia on top of it. So lots of reasons why they could have low oxygen and you're gonna be addressing each one in a different way. I know that, and fever, if you add that to it, think about how the utilization occurs in that scenario and how you can drop your oxygen saturation just from that ton of utilization, much less if you had respiratory compromise on top of it. - Absolutely. And then I'm gonna close out with a last little pearl to remember. - Your favorite. Anemia does not cause hypoxemia. So don't ever blame low oxygen saturations on anemia. It's not a thing. You can have one gram of hemoglobin and it can still be 100% saturated. All the sat tells us is how much oxygen is that hemoglobin molecule carrying? Is it carrying its max amount or is it not carrying the max amount? Whether you have one gram or 14 grams, okay? Now that's different than oxygen content. Your body has to have enough hemoglobin molecules to deliver enough oxygen to all your tissues, but that doesn't mean that it's not saturated. That's a completely different thing. Suzanne, you're nodding your head. - Yeah, well, because how I love to teach that concept is again, this is just a piece of technology that gives us a ton of information, but you have to also look at it in what's going on with the patient. And if you don't know her hemoglobin, then you really can't estimate how much oxygen content that the patient has without that value. So like you said, you could have one, you could have five grams of hemoglobin and it'd be 100% saturated, but she still doesn't have enough oxygen content. Therefore, she's not gonna have adequate oxygen delivery to the tissues and her tissues can still be hypoxic because she doesn't have enough delivery and that is due to the content, but still may be 100% saturated. So one piece of technology does not replace respiratory rate as well as your other clinical assessments that go along with it. - And I talk about all of those concepts and more in the Academy. I have a whole section on oxygen delivery and content and consumption, et cetera, and give some clinical examples there. So if you wanna learn more about this or many other important concepts and high risk and critical care obstetrics, you can find our Academy online at clinicalconceptsinob.com. We're so grateful to you guys for listening and for supporting our podcast. Please subscribe and leave us a review. You can check out our website at clinicalconceptsinob.com. We're on Facebook at clinicalconceptsinobstetrics on X at OB Critical Care and on Instagram at criticalcareob. And as always, email us or send us a direct message for suggestions on future podcasts. (upbeat music) This podcast was produced by Austin Baird. Are you looking to create a podcast? Please email me at podcastnashville@gmail. That is [email protected].