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What Is A Pulse Oximeter?
A Pulse Oximeter is a versatile, mobile, non invasive medical instrument that indirectly measures the oxygen saturation in the blood. It is definitely a convenient replacement to the older procedure of Oximeter which constituted of the need to collect blood samples invasively to perform a list of tests in order to obtain the required results. The pulse oximeter basically shows us how much of oxygen is contained in the blood and is available for the use of the body as a decrease in Oxygen concentration in the body could be very fatal.
- For us to better understand what this interesting piece of equipment or the pulse oximeter does and how it helps us, let's take a minute or two to understand what oxygen saturation is And why it is of any importance to us.
- "Breathing in, breathing out... Breathing in, breathing out..." when would we last stopped to actually make an effort to breath in and breath out, this process has become so part of our everyday lives, that many a times we take this overwhelming mechanism granted which assists the very continuation of "Life" itself.
- Each time we gulp a mouthful of air, a vital substance called oxygen enters our body system via the lungs. When oxygen enters and mixes with the blood at the lungs it could then be transported all over the body to be used and metabolized for the proper functioning of the body, as lack of oxygen in the body could cause hypoxia and bring about a cascade of adverse reactions in the body.
- There are two mechanisms by which oxygen could be coalesced with blood. The first is when oxygen is dissolved in plasma due to the partial pressure difference of oxygen that is present in the surrounding atmosphere and the blood in the lungs. Partial pressure is the pressure exerted by a single component of a mixture of gases, commonly expressed in mm Hg, for a gas dissolved in a liquid, the partial pressure is that of a gas that would be in equilibrium with the dissolved gas. This causes oxygen to dissolve in the plasma of the blood, for each 1mmHg partial pressure of Oxygen 0.003ml dissolves in the plasma.
- The other is when oxygen binds with a compound called hemoglobin that is found in the red blood cells and forms oxyhemoglobin, which thereafter could be transported to all over the body, where the oxygen could be taken up, relieving the hemoglobin back to its original state. Here for every 1mg of hemoglobin. 1.34 ml of oxygen is carried.
- The dissolved fraction is available to tissues first and then, the fraction bound to hemoglobin. So as tissues metabolize oxygen or if oxygen becomes difficult to pick up through the lungs, the dissolved oxygen and the oxygen bound to hemoglobin will eventually become depleted. The dissolved oxygen can be measured by arterial blood gas analysis but this is not yet a practical field application. This fraction is not measured by pulse oximeter.
- The presence of available oxygen in form of oxyhaemoglobin in the blood could be simplified or rather related to what we call the oxygen saturation that is calculated by the pulse oximeter.
- The standard range for oxygen saturation is from 95-100% although a value up to 90% is accepted.
- How does a Pulse Oximeter work?
- The modern Pulse Oximeter contains a pair of small light-emitting diodes (LEDs) facing a photodiode or photo receiver, in between a translucent part of the individuals body is placed - either the earlobe, the toe or more commonly on the finger tip, a part with good blood flow. In infants the foot, the palms or the big toes are commonly used. One of the LED emits Red light at the wave length of 660nm and the other infrared LED emitting at a wavelength of about 920nm. The pulse Oximeter works on the principle that the oxygen saturated blood contained as oxyhaemoglobin absorbs more infrared light than red light contrasting to desaturated hemoglobin(or hemoglobin in its original state) which absorbs more red light than infrared. So the measured ratio of the received red light to Infrared light gives rise to the amount of oxygen saturation in the blood.
- There are two main modes of passing the light through measuring point that is commonly used by the pulse oximeter; namely TRANSMISSION method and REFLECTANCE method. Transmission method uses the concept of having the emitting diode and the photo receiver on opposite sides and passing the light source through the measuring point and the other method being having both diodes side by side and having the light source reflected back. Although both methods are used, the Transmission method is more commonly utilized by today's modern portable oximeter.
- The importance of the Pulse should not be forgotten in this system, because it should be noted that, light from the surrounding tissue will absorb red light and infrared light. The pulse in synchronization with the expansion and contraction of the vessels influenced by the heart beat causes a bouncing signal surge. The surge brings about a change in the amount of red light and infrared light absorbed. This is monitored giving rise to subsequent difference in wavelength absorption which gives the estimate of oxygen saturation in the individual's blood. Hence it has to be noted that a detection of a pulse is necessary for the function of the pulse oximeter.
- Do I need a Pulse Oximeter? And what are the various uses of Pulse Oximeter?
- Do remembering that the Pulse Oximeter measures a very important parameter of our body, that is important in ensuring our survival, the pulse oximeter take not only a prominent role for diagnosis in the medical field but also a great beneficial role for sports personals and pilots.
- With the development of the microprocessor and better sensor, the Pulse Oximeter has stepped into a whole new dimension and gained great acceptance in its clinical application may it be in the hospital institution or at home.
- If we are to break down the uses of a Pulse Oximeter from a clinical point of use, it could be stated that the any patient with unstable oxygenation has significant benefits from this device, this includes patients at the intensive care unit, at operations, recovery, and hospital ward setting. The general assessment of a patient's need for oxygen is the most essential part in maintaining life as life cannot continue in the absence of oxygen may in be gross or cellular. Therefore the pulse oximeter plays an important role as a general condition assessment device just like one that checks blood pressure, sugar levels and cholesterols.
- The pulse oximeter aids in other patient condition evaluation such as blood flow assessment, cardiopulmonary arrest, asthma and seizures. Because of its simplicity, versatility and speed, pulse oximeters are of critical importance in emergency medicine and more of a necessity for patients with respiratory and cardiac problems, for diagnosis of some sleep disorders such as apnea and hypopnea. It has definitely become a gold standard of use in ambulances, patients under anesthesia, neonates in the intensive care, newborn nurseries and delivery suites; the pulse oximeter serves an important role in transport internally within the hospitals and externally in the ambulance and Air transport.
- The function and role of the pulse oximeter could not be forgotten from a general diagnostic value as it is very useful in the initial staging of diagnosis as in PFT lab, exercise lab and the sleep lab. Finally it has a great use as an all-purpose assistant and aids in sub acute care centers and home care patients being an indicator when supplement oxygen should be administered to the patients.
- The use of the Pulse Oximeter is not constrained to the medical institution, the non-medical oximeters are rather sporty versions of the pulse oximeter designed specifically for high altitude performance sports and the aviator market. Often coming as finger tip pulse oximeters, they are designed to provide correct blood Oximetry and pulse rate measurement while in motion. At higher altitude, it should be noted that. Blood oxygen saturation decreases because of reduced amount of oxygen in the air; this makes the finger pulse oximeter a very versatile piece of instrument allowing you to accurately assess how well you are adapting to high altitude, by measuring your saturated blood oxygen content and heart rate.
- Portable, battery operated pulse oximeters are very useful for pilots operating in a non-pressurized aircraft above 10,000 feet where supplemental oxygen is required. Prior to the oximeter's invention, many complicated blood tests needed to be performed. Portable pulse oximeters are also useful for mountain climbers and athletes whose oxygen levels may decrease at high altitudes or with exercise.
- What are the different types of Pulse Oximeter?
- Today's market offers a wide range of Pulse Oximeters available from many well renowned companies specializing in DIGITAL MEDICAL INSTRUMENTS.
- If we are to look for the available models in circulation, it could be broken down into two large categories; one would be fingertip type and the other the handheld model.
- The handheld pulse oximeter has become a vital instrument in the care of infants, children and adults with cardiopulmonary diseases. It is an accurate, simple and non invasive method of measuring arterial oxygen saturation. The handheld pulse oximeter provides an easy and accurate way to monitor the blood oxygen saturation and pulse rate. The size, simplicity and convenience of this pulse oximeter are favorite features among many professionals. The handheld pulse oximeter makes use of a probe, which is placed in the person's finger or earlobe and the reading appears on an easy-to-read liquid crystal display (LCD). The hand-held pulse oximeter is designed for monitoring neonatal through adult patients in almost any setting, from hospital to home, although it is more appropriate in a clinical setting than in the home. It is ideal for spot checks or continuous monitoring.
- The fingertip model is a small, cost effective pulse oximeter accurately measures blood oxygen saturation levels and heartbeat pulse rates on adult patients. It's a very compact and self-contained unit to which you need to simply slip the finger. Seconds afterward, it will display your data on high quality easy-to-read liquid crystal display (LCD). The finger tip pulse oximeter is very simple to use and since there is no special learning needed to use it without any setting up, calibration or adaptive devices, it is ideal for use in the hospital or clinical environment, during an emergency or patient transport, or for in-home use as well. The portability of the fingertip pulse oximeter makes it a very popular choice for home use, sports personals, aviators and for medical professionals who are always on the move, it brings a whole new cost effective solution for spot-checking and short term monitoring.
- A new addition to the fingertip model would be the Pediatric Finger pulse oximeter designed especially for children weighing 5-40kg used for spot-check of oxygen saturation and pulse rate. The pediatric finger pulse oximeter can be used to detect conditions such as hypoxemia, a deficiency in concentration of oxygen in arterial blood, whether due to an inadequate supply or poor circulation.
- What is Sleep Apnea?
- Sleep apnea is a sleeping disorder characterized by intermittent cessation of breathing through the nose and mouth during sleeping, where the term apnea refers to the episode of breathlessness. As a rule, apneas of at least 10 second duration are considered important clinically, but usually apneas last 20 - 30 s and may be as long as 2 to 3 minutes as well.
- Sleep apnea can be categorized as two types; one is Central sleep apnea which is due to neural dysfunction causing all respiratory muscles to cease to working properly. The second type is called obstructive sleep apnea where airflow ceases despite of proper respiratory function, which is due to occlusion or block in the oropharyngeal airway.
- The reason for sleep disorder in Obstructive sleep disorder is because sleep causes the muscle tone to relax and at the level of the throat, the human airway is composed of collapsible walls of soft tissue which can obstruct breathing during sleep. Mild sleep apnea which are experienced during any upper respiratory diseases are not so important, but chronic, severe obstructive sleep apnea requires treatment as it prevents sleep and is the causative agent to other complications, one of the most serious of them being severe forms of congestive heart failures.
- One of the most common symptoms being loud snoring associated with sleepless nights and sleepiness during the day times. The definite investigation for suspected obstructive sleep apnea is
- Polysomnography, which is a detailed overnight sleep study that includes recording of electrographic variables that permit the identification of sleep at various stages.
- Arterial oxygen saturation by ear or finger pulse oximeter.
- Heart rate
- And respiratory variables normally by spirometry that permit the identification of apneas and their classification as central or obstructive.
- Because polysomnography is a time-consuming and expensive test, an overnight recording of arterial oxygen saturation by Oximetry can be used to confirm the diagnosis and obviate the need for a full polysomnography, although a negative result doesn't eliminate the diagnosis but rather mandates that a patients' needs to do a polysomnography.
- Several approaches of treatment are available today, depending on the mechanism involved. In severe cases of obstructive Sleep Apnea (significant daytime sleepiness or >30 obstructive events and arousals per hour of sleep), Nasal continuous positive airway pressure (CPAP) is the treatment of choice. And if patients with obstructive sleep apnea cannot tolerate nasal CPAP, upper airway surgery could be considered.
- If we consider Central Sleep apnea there are many underlying causes for its development, ranging from the control of the respiratory muscles , lack of oxygen , increase of carbon dioxide and cardiovascular diseases to name a few. The symptoms of central sleep apnea are similar to obstructive sleep apnea but are dominated with a history of recurrent respiratory failure, pulmonary hypertension and right- sided heart failure. Complaints of sleeping poorly, morning headaches, morning and daytime fatigue and sleepiness are predominant. It could also be noted that obesity and hypertension are less prominent in central sleep apnea than in obstructive sleep apnea. Unlike in obstructive sleep apnea where a polysomnography is mandatory. Measurements of transcutaneous partial pressure of Carbon dioxide are particularly useful in the diagnosis of Central sleep apnea.
- Hypoxia and Pulse Oximeter#
- The body constantly requires oxygen, whether you are sleeping, thinking, active or inactive; every organ in the body requires more or less oxygen depending upon the degree of the activity taking place. Hypoxia is a condition where there is a deficiency of oxygen in blood or the inability to use the oxygen present in the blood. Although all body tissues are affected drastically due to hypoxia, the brain is by far the most sensitive to a mild oxygen deficit.
- Hypoxia can result from many, number of causes. If we are to look at the most common it could be simplified into a few types. Mechanical or stagnant hypoxia is caused by the restriction of the flow of blood to tissues and cells. The tingling sensation associated with a foot "falling asleep" after sitting in a cramped position results from stagnant hypoxia. Loss of consciousness called by the inability for oxygen to reach the brain due to high G-force is another example of Stagnant hypoxia.
- Another condition of hypoxia is due to Anemia where oxygen carrying ability/capacity of the blood is reduced due to various underlying reasons. This is also called "hyperemic hypoxia" and this situation can arise from drop in hemoglobin count. A very common cause would be severe internal or external bleeding. An alternative instance of hyperemic hypoxia would be when carbon monoxide is present in the blood, as hemoglobin has a higher affinity to carbon monoxide than oxygen. Not only does the carbon monoxide prevent the oxygen from reaching the cells, it is also a metabolic poison, compromising the cell's ability to transport oxygen, this condition is known as Histoxic hypoxia. Where someone affected by this condition may not recover quickly even if the carbon monoxide source is removed and oxygen is supplemented.
- Hypoxia could also be secondary to other underlying diseases such as poorly ventilated alveoli, pulmonary atelectasis and right to left extrapulmonary shunting.
- The final manifestation of hypoxia results from the decreasing amount of oxygen available on ascent in the atmosphere. This deficiency is called "hypoxic hypoxia or altitude hypoxia". It has particularly importance to aviators and sportsmen in high altitude.
- The pulse oximeter measures the oxygen saturation and therefore it has great benefit directly associated in diagnosing hypoxia as soon as possible, showing if supplement oxygen is necessary for administration.
- The Advantages and Disadvantages of the Pulse oximeter
- The advantages of the pulse oximeter could be listed as follows:
- Affordable Price: almost all pulse oximeter are at quite an affordable price in the market.
- Fast: Provides real-time, absolute measurement of oxygen levels without the use of empirical tables.
- Versatile: it can be used virtually anywhere - hospital or home - to determine oxygen levels.
- Accurate: the pulse oximeter provides a relatively accurate measure which could be taken into account for a proper diagnosis
- Extended use: The patient mobility makes this technology suitable for long-term patient monitoring.
- Noninvasive sampling: The accuracy of this technology allows doctors, clinics and hospitals to replace traditional invasive sampling procedures, such as arterial puncture or an indwelling arterial catheter, for obtaining absolute oxygen measurement.
- Ease of use: Does not require preliminary calibration.
- If the disadvantages or risks are to be considered, we could say there is no documented cases of genuine side effects that have been recorded by the pulse oximeter. But there are a few draw backs that could be noted.
- One of the greatest draw back would be although a pulse oximeter is used to monitor oxygenation, it cannot determine the metabolism of oxygen, or the amount of oxygen being used by a patient. For this purpose, it is necessary to also measure carbon dioxide (CO2) levels.
- The pulse oximeter also fails to function properly when there is a reduction of peripheral blood flow as in peripheral vasoconstriction, severe hypotension, cold, cardiac failure, some cardiac arrthymias and peripheral vascular diseases. This is due to inadequate signal for analysis.
- Venous congestion due to tricuspid regurgitation and various systemic abnormal pulsations can produce low reading.
- Bright overhead lights in surgical rooms and shivering can cause an error in the reading.
- Another huge problem would be the inability to distinguish between different forms of hemoglobin as in methemoglobin and carboxyhemoglobin. Where low saturations of hemoglobin with oxygen due to the presence of these other forms can bring about a false high saturation value.
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