Overview of Oxygen Saturation
Oxygen saturation is a crucial measurement in taking care of patients. This is because oxygen levels need to be closely watched in the body. If the oxygen level, or hypoxemia, drops too low, it can negatively affect important organs like the brain, heart, and kidneys.
What exactly is oxygen saturation? It’s a measure of how much oxygen is attached to a protein in our blood cells called hemoglobin, in comparison to the amount of hemoglobin that does not have oxygen attached to it. Each hemoglobin protein has four parts, each of which can bind with an oxygen molecule. So, every hemoglobin protein can carry up to four molecules of oxygen when it’s moving around the bloodstream.
Given how important it is for our tissues to have enough oxygen, we have to keep tabs on our current oxygen saturation. To do that, we can use a tool called a pulse oximeter. This is a simple, painless device that you can clip onto your finger. It measures the light wavelengths that pass through your finger to figure out the ratio of oxygen-filled hemoglobin to hemoglobin without oxygen. This device has become so crucial in medicine that many consider it as important as checking your temperature, pulse, respiration, and blood pressure, the four vital signs.
So, healthcare professionals have to be familiar with how pulse oximetry works, and its strengths and limitations. They also should understand the fundamentals of oxygen saturation, as these measurements play a key role in patient care.
Anatomy and Physiology of Oxygen Saturation
The body’s use of oxygen is partly measured by how much oxygen is in the blood entering the body (arterial) compared to the amount in the blood leaving the body (venous), plus how fast the blood is flowing. Oxygen is necessary for the body to change glucose (a type of sugar) into pyruvate, a process which releases an energy source the body needs called ATP.
In the bloodstream, a protein called hemoglobin quickly grabs free oxygen to create a combined substance known as oxyhemoglobin. This only leaves a tiny amount of free oxygen in the plasma, the liquid part of blood. This relationship can be shown in a graph called the oxygen-hemoglobin dissociation curve. This curve shows how much of the hemoglobin is saturated, or filled up, with oxygen based on the pressure of the oxygen.
Hemoglobin can get completely saturated, with every part able to hold onto oxygen, when the oxygen pressure is at 100 mmHg. Every gram of hemoglobin can carry 1.34 mL of oxygen. The dissolved oxygen is such a small part of the total oxygen in the blood that you could consider the oxygen content of blood to be just the oxyhemoglobin levels.
When the oxygen pressure gets lower, so does the percentage of saturated hemoglobin. The curve showing this connection is a special kind of curve called a sigmoidal curve. Basically, each time an oxygen molecule binds, or attaches itself to hemoglobin, the hemoglobin changes shape to make room for more oxygen to bind. And each time an oxygen attaches, it becomes easier for the next oxygen to attach. So, the fourth oxygen molecule will have the easiest time attaching.
In the lungs, oxygen pressure is 100 mmHg due to the high amount of oxygen available there. However, since it’s so easy for the fourth oxygen molecule to attach to hemoglobin, oxygen saturation can stay high even when the pressure is lower, like 60 mmHg. But if the pressure falls far enough, like down to 40 mmHg or 25 mmHg, then hemoglobin saturation will start to fall rapidly. There’s a specific term, P50, used to refer to the level where half of the oxygen-holding parts of each hemoglobin have one molecule of oxygen attached.
Different factors can cause shifts in the oxygen-hemoglobin dissociation curve. A “right shift” means that hemoglobin is less attracted to oxygen, which allows more oxygen to be available to the body’s tissues. A helpful way to remember what causes a right shift is “CADET, face Right!” This acronym stands for: PCO2, Acid, 2,3-diphosphoglycerate, Exercise, and Temperature. The dissociation curve shifts to the right if any of these factors increase.
On the other hand, a “left shift” means that hemoglobin’s attraction to oxygen has increased, which in turn reduces the amount of oxygen available to body tissues. A left shift can be caused by decreases in temperature, PCO2, acidity, and 2,3-bisphosphoglyceric acid, formerly called 2,3-diphosphoglycerate.
Why do People Need Oxygen Saturation
Pulse oximetry is a quick, non-invasive method used to measure the amount of oxygen in your blood. It is useful in many situations because it provides an accurate reading of how well your body is absorbing oxygen. This tool is especially invaluable in emergency situations when symptoms of low oxygen levels might not be physically noticeable.
Low oxygen levels, also known as hypoxemia, can occur for numerous reasons and in many different settings. In such situations, pulse oximetry can help. Places where pulse oximetry is often used include emergency departments, operation theaters, post-surgery recovery rooms, oral surgery suites, labor and delivery units, and even at home.
Other areas where its use could be beneficial include facilities where sleep and exercise studies are conducted, units that cater to patient transfers between facilities, places used for conscious sedation procedures, heart-related procedure suites, and facilities designed for high-altitude conditions or aerospace medicine.
No matter where it is employed, pulse oximetry serves as a reliable method for checking oxygen levels, playing an essential role in maintaining patient health and wellbeing.
When a Person Should Avoid Oxygen Saturation
Using a pulse oximeter, a device that checks the level of oxygen in your blood, doesn’t usually pose problems. However, it’s important to know what it can and can’t do. For instance, if there’s a need to measure other aspects of your blood like pH, PaCO2 (a measure of carbon dioxide), total hemoglobin (the protein that carries oxygen), and abnormal hemoglobin (like in cases of carbon monoxide poisoning), a pulse oximeter might not be the best choice.
Another vital thing is to monitor where the pulse oximeter is placed for any changes, such as skin blisters or damage to the area underneath your nails. In case of patients with burns, it’s necessary to move the pulse oximeter around every 2 to 4 hours.
Equipment used for Oxygen Saturation
A pulse oximeter is a device that helps measure how much oxygen is in your blood. It has a part called a probe, which contains light-emitting tools (LEDs) and a light detector. The LEDs shine light at controlled, chosen wavelengths. This light then goes through the blood vessels in parts of the body such as your fingertip or earlobe.
The way the pulse oximeter works is based on a scientific law called the Beer-Lambert law of light absorption. This law explains how light is absorbed as it goes through a clear substance, like plasma in our blood, that has something in it, like hemoglobin, that takes in light at a certain wavelength. Hemoglobin is a protein in our blood that carries oxygen.
The amount of light absorbed by oxygen-rich and oxygen-poor hemoglobin is different. This is why blood with lots of oxygen (arterial blood) looks red, while blood with less oxygen (venous blood) looks blue. But, because our body tissues also take in some light, it’s hard to figure out the exact amount of oxygen-rich hemoglobin in the body by just shining light into the skin.
To solve this problem, the pulse oximeter’s probe sends out quick light pulses—one red and one infrared—through the skin where it is attached. On the other side of the skin, the detector measures how much of this light gets through. The differences in the amount of transmitted light, as they switch between red and infrared, are recorded. These measurements are then processed using a formula in a tiny computer. This gives us the final reading of how saturated our blood is with oxygen, which is then shown on the device’s screen.
Who is needed to perform Oxygen Saturation?
Everyone in the medical field should learn about a tool called a pulse oximeter, which measures the oxygen level in your blood. This basic knowledge is very important for them to properly use and understand the device.
The people who more frequently use pulse oximeters, like doctors or nurses, find it particularly useful to understand how this tool’s readings relate to the amount of hemoglobin (a protein in your red blood cells that carries oxygen) in your blood.
They also need to understand how these readings can change due to the oxygen-hemoglobin dissociation curve. This curve simply describes how easily oxygen leaves the hemoglobin and goes into the body’s tissues which need it. Understanding this can help them interpret the readings from the pulse oximeter more effectively.
Preparing for Oxygen Saturation
When using a pulse oximeter, the most important step is to place the device in a position where its light can easily reach the sensor. There are several factors to consider before using the pulse oximeter. Nail polish should be removed and the finger should be cleaned with alcohol. Check the finger for anything that might block the light, such as a tattoo. Bright, natural light can sometimes affect the accuracy of the pulse oximeter’s readings. To prevent this, make sure the rubber cover on the pulse oximeter is in place as it helps reduce the input of light from the environment.
How is Oxygen Saturation performed
To use a pulse oximeter, you should first make sure you’re placing it in the right spot. Put the device so the light it emits can go through your skin and reach the sensor on the other side. If you are placing the pulse oximeter on your finger, make sure it fits well – not too tight and not too loose. Be careful that it doesn’t cut off your blood circulation because that can lead to a wrong reading. There are also pulse oximeters that can be placed on the earlobe. During emergencies, you may put the pulse oximeter sideways on your finger, especially if you have nail polish or colored skin that may block the light.
Possible Complications of Oxygen Saturation
Pulse oximeters, the devices that check how well your blood carries oxygen, are usually safe to use. But in some rare cases, they can cause minor issues like blisters, nail damage, or, very rarely, electrical shocks or burns if the probe doesn’t fit well or is substituted.
These are a few ways to get more accurate readings from your pulse oximeter:
* Warm up and gently rub your skin before using it
* You could try applying a special medicine to your skin to increase blood flow (a topical vasodilator)
* Try using the oximeter on a different part of your body such as your ear
* Try a different probe or device
Certain factors might cause your pulse oximeter to give less accurate readings. These include wearing nail polish, having darker skin pigmentation, being in bright sunlight, moving around a lot when using it, having poor circulation, having abnormal forms of hemoglobin in your blood, using certain medical dyes, and low oxygen levels in the blood.
It’s important to remember that pulse oximeters don’t always give a perfect reading, and treating an inaccurate reading as though it’s accurate can cause problems. For example, getting a false normal oxygen reading when your oxygen is low (false negative), or a false abnormal reading when your oxygen levels are normal (false positive) can lead to inappropriate treatment.
Specific situations can lead to incorrect readings. For example, carbon monoxide can give a false normal reading because it absorbs light similarly to oxygen in the blood. Also, for people with type 2 diabetes, when a specific type of hemoglobin (glycohemoglobin A1c) is higher than 7%, oxygen levels might be overestimated. In these cases, a blood test to measure oxygen levels directly (arterial blood gas) might be needed to get accurate results.
In certain situations, the pulse oximeter might report lower oxygen levels than what’s true. Some of these situations include having different forms of hemoglobin in the blood caused by genetic differences or certain diseases, severe anemia, or blood congestion in the veins.
What Else Should I Know About Oxygen Saturation?
The human eye isn’t very good at recognizing low levels of oxygen in the blood, also called hypoxemia. A blue coloration in the tongue and the protective coating inside the body (mucous membranes) indicates this condition best. This usually happens when the oxygen saturation, or how full of oxygen the blood is, drops to around 75%.
A tool called a pulse oximeter is useful in this case. It non-invasively measures the oxygen saturation in the blood, giving ongoing readings. It can also help to prevent medical errors. On average, pulse oximetry has an accuracy rate of 92% in detecting oxygen deficiency when the saturation is 92%.
It’s hard to determine the exact oxygen saturation level at which hypoxemia sets in. However, the general agreement is that an oxygen saturation below 95% at rest is abnormal. Therefore, watching patients for signs of hypoxemia is crucial.
The brain is the organ most affected by hypoxemia. When oxygen saturation drops below 80% to 85%, changes may occur in vision, thinking, and brain activity (measured by electroencephalography). It is still unclear whether hypoxemia can cause long-term damage. Patients who experience nocturnal (night-time) hypoxemia do not seem to develop serious complications despite their low oxygen saturation levels.
