Oxygen enters the lungs and then is passed on into blood. The blood carries the oxygen to the various organs in our body. The main way oxygen is carried in our blood is by means of hemoglobin. The oxygen molecules get into these cars and travel around the body till they reach their destination. The hemoglobin without oxygen we will call de oxygenated hemoglobin deoxy Hb.
The hemoglobin with oxygen, we will call oxygenated hemoglobin oxy Hb. Oxygen saturation simply refers to the percentage of the available hemoglobin that carries oxygen. Take the situations below. There are 16 hemoglobin units and none of the 16 have oxygen. So in summary, oxygen saturation tells you the percentage of the total hemoglobin that is carrying oxygen.
Pulse oximetry uses light to work out oxygen saturation. Light is emitted from light sources which goes across the pulse oximeter probe and reaches the light detector.
If a finger is placed in between the light source and the light detector, the light will now have to pass through the finger to reach the detector. Part of the light will be absorbed by the finger and the part not absorbed reaches the light detector.
The amount of light that is absorbed by the finger depends on many physical properties and these properties are used by the pulse oximeter to calculate the oxygen saturation. The physical properties that a pulse oximeter employs will be explained using the probe shown below. A finger is shown inserted into the probe. Above the finger are the light sources that emit light.
In the finger is an artery which carries the blood the pulse oximeter is interested in and a vein through which the blood leaves the finger. Below the finger is the light detector. Hemoglobin Hb absorbs light. The amount of light absorbed is proportional to the concentration of Hb in the blood vessel. In the diagram below, the blood vessels in both fingers have the same diameter.
However, one blood vessel has a low Hb concentration i. Each single Hb absorbs some of the light, so more the Hb per unit area, more is the light is absorbed. By measuring how much light reaches the light detector, the pulse oximeter knows how much light has been absorbed.
More the Hb in the finger , more is the light absorbed. Look at the two fingers shown below. Both arteries have the same concentration same Hb per unit area, blue square However, the artery on right is wider than the one on the left.
The light emitted from the source has to travel through the artery. The light travels in a shorter path in the narrow artery and travels through a longer path in the wider artery paths are shown as green lines below. Though the concentration of Hb is the same in both arteries, the light meets more Hb in the wider artery, since it travels in a longer path.
Therefore, longer the path the light has to travel, more is the light absorbed. We have seen how concentration and light path affect the absorbance of light.
In addition to these, the pulse oximeter makes use of another important property to calculate oxygen saturation. That is, oxy hemoglobin and deoxy hemoglobin absorb light of different wavelengths in a specific way.
Before we go further, we need to remember what wavelength is. All light is composed of waves. For an example, the wave on the left has a wavelength of nm and the wave on the right has a longer wavelength of nm. The pulse oximeter uses the property that oxyhemoglobin and deoxyhemoglobin absorb light of different wavelengths in a specific way. This property can be demonstrated in a laboratory as will be now described.
We can first demonstrate how oxyhemoglobin absorbs light of different wavelengths in a specific way. We use a special light source of which we can adjust the wavelength of the light it emits. This light source sequentially passes light of different wavelengths through a sample of oxy Hb.
The detector notes how much light, at each wavelength, has been absorbed. A graph for the absorbance of oxy hemoglobin at different wavelengths will look like this. Again notice , how like oxy Hb, Deoxy Hb absorbs different amount of light at different wavelengths. Now let us see the absorbance graph of oxy Hb and the absorbance graph of deoxy Hb together so you can compare them.
Note how each of them absorbs light of different wavelengths very differently. One is a red light, which has a wavelength of approximately nm. The other is an infrared light, which has a wavelength of nm. Throughout our description, we will show the infrared light in light blue. In reality, infrared light is invisible to the human eye. Now look at the oxy Hb absorbance graph again, but this time paying attention to the wavelengths of light used in pulse oximeters. You will see that oxy Hb absorbs more infrared light than red light.
Below is the graph that shows the absorbance of deoxy Hb. It is seen from the graph that deoxy Hb absorbs more Red light than Infrared light. To make the comparison of absorbance of oxy Hb and deoxy Hb easier, here is a composite graph showing the absorbance of both. You will see that :. You might find the memory aide below useful to remember the wavelengths absorbed by oxy Hb and deoxy Hb. The pulse oximeter works out the oxygen saturation by comparing how much red light and infra red light is absorbed by the blood.
Depending on the amounts of oxy Hb and deoxy Hb present, the ratio of the amount of red light absorbed compared to the amount of infrared light absorbed changes. The absorbance ratio i. The blood has both , oxy Hb and deoxy Hb. The absorbance pattern is now somewhere in between the oxy Hb curve and deoxy Hb curve both shown in grey. The animation below shows what you have seen before. As the amount of oxy Hb and deoxy Hb changes, the light ratio comparing red and infrared light also changes.
The pulse oximeter uses the ratio to work out the oxygen saturation. Unfortunately, there is a problem. In physics, the Beer and Lambert law have very strict criteria to be accurate.
For an example, the light that goes through the sample should go straight through like the lights rays in the image below. However, in real life , this does not happen. Blood is not a neat red liquid. Instead, it is full of various irregular objects such as red cells etc.
This makes the light scatter, instead of going in a straight line. Therefore Beer and Lamberts Law cannot be applied strictly. Because Beer and Lamberts law cannot be applied strictly, there would be errors if they were used to directly calculate oxygen saturation. A test pulse oximeter is first calibrated using human volunteers. The test pulse oximeter is attached to the volunteer and then the volunteer is asked to breath lower and lower oxygen concentrations.
At intervals, arterial blood samples are taken. As the volunteers blood desaturates, direct measurements made on the arterial blood are compared simultaneously with the readings shown by the test pulse oximeter. In this way, the errors due to the inability of applying Beers and Lamberts law strictly are noted and a correction calibration graph is made.
A copy of this correction calibration graph is available inside the pulse oximeters in clinical use. When doing its calculations, the computer refers to the calibration graph and corrects the final reading displayed. For saturations below this, the calibration curve is mathematically estimated.
In a body part such as a finger, arterial blood is not the only thing that absorbs light. Skin and other tissues also absorb some light. This poses a problem , because the pulse oximeter should only analyse arterial blood while ignoring the absorbance of light by surrounding tissues. For an example of how tissues can interfere, take the two situations shown below.
One is a thin finger and the other is a fat finger. The tissues in the thin finger absorbs only a little extra light, while the fatter finger shown on the right absorbs much more light. Fortunately, there is a clever solution to the problem. The pulse oximeter wants to only analyse arterial blood, ignoring the other tissues around the blood.
Luckily, arterial blood is the only thing pulsating in the finger. Everything else is non pulsating. As shown below, the computer subtracts the non changing part of the absorbance signal from the total signal. In this way, the pulse oximeter is able to calculate the oxygen saturation in arterial blood while ignoring the effects of the surrounding tissues. The diagrams used so far have exaggerated the size of the pulsatile part to make it easy for you to see and understand. However, in reality, the pulsatile signal is very small.
However, if the nausea is severe, you may want to talk to your doctor about taking an anti-nausea drug for a few days. Nausea, vomiting and diarrhoea is often less severe for people who take fentanyl in comparison to other opioid drugs.
Therefore, if you experience severe gastrointestinal effects while taking a different opioid, switching to fentanyl may help. Constipation is a common side effect that occurs to almost everyone who takes fentanyl for chronic pain. Unfortunately, this doesn't get better with time and you usually need to do something to help with digestion in your body. It is helpful to:. If you are experiencing constipation while taking fentanyl, have a chat to your doctor or pharmacist about the best options for you.
In severe cases, this can lead to coma or death. Usually by the time you notice changes in breathing it's too late.
Instead, focus on how awake the person is. They should be easy to rouse and be able to stay awake. If they're not easy to rouse, a lower opioid dose is probably needed. Over time, your body can get used to taking fentanyl and begin to depend the medications.
This means that if you stop taking the drug, you may notice withdrawal symptoms such as:. This happens most often when people take fentanyl for a long time, such as if you are taking it for chronic pain. There are some people who may need special attention if they take oxycodone due to other medications or health conditions they have. For example, if you have the following conditions often you may need a lower dose than usual:.
Additionally, people with epilepsy are more likely to have a seizure while taking oxycodone, so this should be considered. People who are elderly often require a lower dose of oxycodone than other adults, particularly if they have poor kidney or liver function.
This is because their body takes longer to process the drug, so the concentration in the bloodstream builds up more quickly. As a result, elderly people are more likely to experience side effects, such as cognitive impairment, sedation and respiratory depression. They may also be at risk for having a fall. Taking oxycodone at the same time as another drug can sometimes change their effect on your body because of the way they interact. If you take it at the same time as rifampicin or St John's Wort , your body will metabolize oxycodone more quickly.
If you take it at the same time as ritonavir or voriconazole , your body will metabolize oxycodone more slowly. Any medication that blocks the action of opioids, such as buprenorphine , naloxone or naltrexone, can decrease the action of oxycodone. These drugs are not usually used together. All drugs that cause your breathing to slow down can increase the risk of a serious side effect of oxycodone: respiratory depression.
Many drugs to lower blood pressure, such as beta blockers, can have this effect. This combination can be used, but it's important that your doctor knows that you are taking oxycodone and checks that the dose is right for your body. Some drugs that are used in the treatment of depression called selective seretonin reuptake inhibitors SSRIs can cause a condition called seretonin toxicity.
The risk of this is higher if oxycodone is taken at the same time, so you need to be on the lookout for early signs. Instead, it is best for pregnant women to take other medications ato relieve pain while they are pregnant, such as paracetamol. For women who are breastfeeding, occasional doses of oxycodone may be used.
There may still be some risk to your baby if they are used everyday for an extended period of time, so it is best to keep the treatment time short, if possible. Yolanda is a passionate medical writer who loves to help people understand how health and different treatments work. After graduating in Pharmacy in Australia, she moved to Italy to study the Mediterranean way of life and continue learning about health and medicine.
Save my name, email, and website in this browser for the next time I comment.
0コメント