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Pulse oximetry: method essence, indications and application, norm and deviations


Blood gasometry is done strictly as prescribed by the doctor. The reason for this appointment may be:

  1. Sleep apnea - respiratory arrest. This usually happens with people snoring in a dream. When powerful snoring temporarily stops, and after a few seconds it resumes with a terrible sob, characteristic of a lack of air. Most often, household members testify to this. The sleeper himself is rarely able to appreciate the seriousness of respiratory arrest.
  2. Heart failure, when even a slight load causes shortness of breath and lack of air.
  3. The so-called COPD is a chronic obstructive pulmonary disease.
  4. Asthma, which is accompanied by suffocation during a cough.
  5. Cystic fibrosis is a systemic hereditary disease characterized by severe impaired respiratory and gastrointestinal functions.
  6. Pneumonia is an acute and chronic form when weakness and shortness of breath occur even with the patient's banal movement around the room.
  7. Lungs' cancer.

This procedure is prescribed before the upcoming operation or temporary artificial lung ventilation.

How is blood gasometry

In fact, for the patient, this procedure looks like a normal blood sampling, but not from a vein, but from an artery. There may be two options:

  1. Wrist blood sampling,
  2. Blood collection from the inguinal artery.

In either case, the procedure itself is neither particularly painful nor dangerous. Possible consequences of blood sampling from an artery:

  1. A bruise on the wrist or groin. To avoid this, hold cotton wool with alcohol at the puncture site for at least 10 minutes, pinching this place.
  2. Minor bleeding from a punctured artery is possible, especially if the patient takes medications that change blood coagulation - Aspirin Cardio or Vefarin. In this case, it is necessary to warn the doctor in advance about taking all medications on the eve of blood gasometry.
  3. In order to prevent repeated bleeding from the puncture site, one should not load the arm from which the blood was taken for 2-3 days.
  4. As the blood is drawn from the artery, the patient may experience a feeling of slight dizziness or lightheadedness. This standing passes quickly and does not require any medical intervention. Most often, such sensations are absent.

The procedure itself takes several minutes. The puncture site is disinfected, in some cases local anesthesia is done when the patient has a high threshold for pain sensitivity. Usually, the tenderness of the procedure is within the permissible norm.

Blood taken from an artery is transferred to a laboratory for examination.

What does blood gasmetry show?

A laboratory study of the collected blood sample will show the following:

  • partial pressure of oxygen in the blood, which should normally be in the range of 75-100 mmHg,
  • partial pressure of carbon dioxide in the blood, the norm of which is from 38 to 42 mmHg.

However, the final conclusion about this study will be made by a doctor who will take into account:

  • patient age
  • body temperature
  • altitude above sea level
  • the presence of chronic diseases
  • whether the patient is a smoker.

Given all these features, the doctor will conclude: is the blood test indicator critical or is it not worth worrying?

Pulse Oximetry Principle

Depending on how saturated hemoglobin is with oxygen, the length of the light wave that it is able to absorb varies. This principle is based on the operation of a pulse oximeter consisting of a light source, sensors, a detector and an analyzing processor.

A light source emits waves in the red and infrared spectra, and blood absorbs them depending on the number of oxygen molecules bound by hemoglobin. Bound hemoglobin traps the infrared flux, while non-oxygenated traps red. Not absorbed light is detected by the detector, the device calculates the saturation and gives the result to the monitor. The method is non-invasive, painless, and its implementation takes only 10-20 seconds.

Today, two methods of pulse oximetry are used:

At transmissionpulse oximetry the light flux penetrates through the tissue, therefore, to obtain saturation indicators, the emitter and the sensing sensor must be placed on opposite sides, between them - the fabric. For the convenience of the study, sensors are applied to small areas of the body - finger, nose, auricle.

Reflected Pulse Oximetry involves the registration of light waves that are not absorbed by oxygenated hemoglobin and are reflected from the tissue. This method is convenient for use in various parts of the body where it is technically impossible to position the sensors opposite each other or the distance between them will be too large for recording light fluxes - stomach, face, shoulder, and forearm. The ability to choose a study site gives a great advantage of reflected pulse oximetry, although the accuracy and information content of both methods are approximately the same.

Non-invasive pulse oximetry has some drawbacks, including a change in operation in bright light, moving objects, the presence of dyes (nail polish), the need for accurate positioning of the sensors. Errors in the readings can be associated with improper application of the device, shock, hypovolemia in the patient, when the device can not catch the pulse wave. Carbon monoxide poisoning can even show one hundred percent saturation, while hemoglobin is not saturated with oxygen, but with CO.

Areas of application and indications for pulse oximetry

The human body provides for “reserves” of food and water, but oxygen is not stored in it, so in a few minutes after the cessation of its intake irreversible processes begin, leading to death. All organs suffer, and to a greater extent - vital ones.

Chronic oxygenation disorders contribute to deep trophic disorders, which affects well-being. Headaches, dizziness, drowsiness appear, memory and mental activity weaken, prerequisites for arrhythmias, heart attacks, and hypertension appear.

The doctor at the reception or at the examination of the patient at home is always “armed” with a stethoscope and tonometer, but it would be nice to have a portable pulse oximeter with you, because the definition of saturation is of great importance for a wide range of patients with pathologies of the heart, lungs, and blood system. In developed countries, these devices are used not only in clinics: general practitioners, cardiologists, pulmonologists actively use them in everyday work.

Unfortunately, in Russia and other countries of the post-Soviet space, pulse oximetry is carried out exclusively in intensive care units, in the treatment of patients one step away from death. This is due not only to the high cost of the devices, but also to the lack of awareness of the doctors themselves about the importance of measuring saturation.

Determination of blood oxygenation serves as an important criterion for the patient’s condition during anesthesia, transportation of seriously ill patients, during surgical operations, therefore it is widely used in the practice of anesthetists and resuscitators.

Premature newborns, who, due to hypoxia, have a high risk of damage to the retina of the eye and lungs, also need pulse oximetry and constant monitoring of blood saturation.

In therapeutic practice, pulse oximetry is used for pathology of the respiratory system with their insufficiency, sleep disturbances with respiratory arrest, presumed cyanosis of various etiologies, in order to control the treatment of chronic pathology.

Indications for pulse oximetry consider:

  • Respiratory failure, regardless of its causes,
  • Oxygen therapy
  • Anesthetic aid for operations,
  • The postoperative period, especially in vascular surgery, orthopedics,
  • Deep hypoxia in the pathology of internal organs, blood system, congenital anomalies of red blood cells, etc.,
  • Probable syndrome of nocturnal apnea (respiratory arrest), chronic nocturnal hypoxemia.

Pulse oximetry at night

In some cases, there is a need to measure saturation at night. Some conditions are accompanied by respiratory arrest when the patient is sleeping, which is very dangerous and even threatens death. Such nightly attacks of apnea are not uncommon in individuals with a high degree of obesity, pathology of the thyroid gland, lungs, and hypertension.

Patients suffering from respiratory disorders in a dream complain of night snoring, poor sleep, daytime sleepiness and a feeling of lack of sleep, heart failure, headache. These symptoms suggest thoughts of probable hypoxia during sleep, which can only be confirmed with a special study.

Computer pulse oximetry performed at night takes many hours, during which saturation, pulse, and the nature of the pulse wave are controlled. The device determines the oxygen concentration per night up to 30 thousand times, storing each indicator in memory. It is not necessary for the patient to be in the hospital at this time, although often his condition requires it. In the absence of risk to life from the underlying disease, pulse oximetry is performed at home.

The pulse oximetry algorithm in a dream includes:

  1. Fixing the sensor on the finger and the sensing device on the wrist of one of the hands. The device turns on automatically.
  2. Throughout the night, the pulse oximeter remains on the arm, and each time the patient wakes up, this is recorded in a special diary.
  3. In the morning, waking up, the patient removes the device, and gives the diary to the attending physician to analyze the data.

Analysis of the results is carried out for the interval from ten in the evening until eight in the morning. At this time, the patient should sleep in comfortable conditions, with an air temperature of about 20-23 degrees. Before going to bed, sleeping pills, coffee and tea are excluded. Any action - awakening, taking medication, a headache attack - is recorded in the diary. If during sleep a decrease in saturation is established to 88% or lower, then the patient needs prolonged oxygen therapy at night.

Indications for night pulse oximetry:

  • Obesity, starting from the second degree,
  • Chronic obstructive pulmonary disease with respiratory failure,
  • Hypertension and heart failure, starting from the second degree,
  • Myxedema.

If a specific diagnosis has not yet been established, then signs indicating possible hypoxia, and, therefore, an occasion for pulse oximetry, will be: night snoring and respiratory arrest during sleep, shortness of breath at night, sweating, sleep disturbances with frequent awakenings, headache and feeling fatigue.

Saturation and deviation rates

Pulse oximetry is aimed at establishing the oxygen concentration in hemoglobin and pulse rate. The norm of saturation is the same for an adult and a child and is 95-98%in venous blood - usually within 75%. A decrease in this indicator indicates developing hypoxia, an increase is usually observed during oxygen therapy.

Upon reaching the figure of 94%, the doctor must take urgent measures to combat hypoxia, and saturation of 90% and below is considered critical when the patient needs emergency care. Most pulse oximeters emit sound signals at dysfunctional indicators. They respond to a decrease in oxygen saturation below 90%, the disappearance or slowdown of the pulse, tachycardia.

The measurement of saturation refers to arterial blood, because it carries oxygen to the tissues, so the analysis of the venous bed from this position does not seem to be diagnostically valuable or advisable. With a decrease in total blood volume, arterial spasm, pulse oximetry indicators may change, not always showing the actual saturation figures.

The pulse at rest in an adult varies between 60 and 90 beats per minute, in children, heart rate depends on age, so the values ​​will be different for each age category. In newborn babies, it reaches 140 beats per minute, gradually decreasing as it grows to adolescence to the norm of an adult.

Depending on the proposed location for performing pulse oximetry, the devices can be stationary, with sensors on the hands, for night monitoring, and waist zones. Stationary pulse oximeters are used in clinics, have many different sensors and store a huge amount of information.

As portable devices, the most popular are those in which the sensors are fixed on the finger. They are easy to use, do not take up much space, can be used at home.

Chronic respiratory failure against the background of pathology of the lungs or heart appears in the diagnoses of many patients, but close attention is not given to the problem of blood oxygenation. The patient is prescribed all kinds of drugs to combat the underlying disease, and the question of the need for long-term oxygen therapy remains outside the discussion.

The main method for diagnosing hypoxia in case of severe respiratory failure is to determine the concentration of gases in the blood. At home and even in the clinic, these studies are usually not carried out, not only because of the possible lack of laboratory conditions, but also because doctors do not prescribe them to the "chronicles" that are observed on an outpatient basis and maintain a stable state.

On the other hand, having fixed the fact of the presence of hypoxemia with the help of a simple pulse oximeter device, the therapist or cardiologist could well have sent the patient to oxygen therapy. This is not a panacea for respiratory failure, but the ability to extend life and reduce the risk of nocturnal apnea with death. The tonometer is known to all, and patients themselves actively use it, but if the prevalence of the tonometer was the same as the pulse oximeter, then the frequency of detecting hypertension would be many times lower.

Timely prescribed oxygen therapy improves the patient’s well-being and prognosis of the disease, prolongs life and reduces the risks of dangerous complications, therefore, pulse oximetry is the same necessary procedure as measuring pressure or pulse rate.

Pulse oximetry in obese subjects occupies a special place. Already in the second stage of the disease, when a person is still called a “chubby” or simply very well-fed, serious respiratory disorders are possible. Stopping him in a dream contributes to sudden death, and relatives will be perplexed, because the patient could be young, well-fed, rosy, and quite healthy. Determining sleep saturation in obesity is a common practice in foreign clinics, and the timely use of oxygen prevents the death of overweight people.

The development of modern medical technologies and the appearance of devices accessible to a wide range of patients help in the early diagnosis of many dangerous diseases, and the use of portable pulse oximeters is already a reality in developed countries, which is gradually coming to us, so I hope that soon the pulse oximetry method will be the same common, like using a tonometer, glucometer or thermometer.

What blood oxygen levels show

Blood oxygen levels are a measure of how much oxygen your red blood cells carry. Your body closely regulates the level of oxygen in the blood. Maintaining an accurate balance of oxygenated blood is vital to your health.

Most children and adults should not control blood oxygen levels. In fact, many doctors will not check this unless you have signs of a problem, such as shortness of breath or chest pain.

However, for people with chronic health conditions, many need to control the level of oxygen in the blood. This includes asthma, heart disease, and chronic obstructive pulmonary disease (COPD). In these cases, monitoring oxygen levels in the blood can help determine if the procedures are working, or if they need to be adjusted.

Keep reading to find out where your blood oxygen level should be, what symptoms you may experience if your level is off, and what happens next.

Measuring tools

Pulse Oximetry of Blood Oxygen

This method is considered less informative and accurate compared with gasometry in determining the level of oxygen in the blood, but less traumatic. Therefore, it is precisely this method that is used most often. Indications for this study are no different from gasometric studies. And the method itself is as follows:

  1. Infrared radiation is passed through body tissues. Hemoglobin, saturated with oxygen, absorbs infrared rays, and free hemoglobin only red rays.
  2. A special processor reads the sensor readings about the percentage of free and oxygen-rich hemoglobin and gives the result on the monitor - what is the level of oxygen in the blood.
  3. This procedure is carried out by a special device that is attached to the finger, earlobe or tip of the nose. С одной стороны закреплен излучатель инфракрасного света, с другой – датчик с процессором.

Метод не имеет противопоказаний, однако может потребоваться специальная подготовка – снять лак с ногтей, если датчик крепится к 3-й фаланге пальца, ограничить количество выкуриваемых накануне исследования сигарет. А перед самой процедурой не курить хотя бы 2 часа. The procedure itself takes several minutes and the result is known immediately. But in this case, the interpretation of this study is the prerogative of the doctor, not the patient.

Arterial blood

Arterial Blood Gas (ABG) - A blood test. It measures the level of oxygen in the blood. It can also detect the level of other gases in the blood, as well as the pH level (acid / base level). ABG is very accurate, but it is invasive.

To get an ABG measurement, your doctor will draw blood from an artery, not a vein. Unlike veins, arteries have a pulse that can be felt. In addition, blood drawn from arteries is oxidized. There is no blood in your veins.

An artery in your wrist is used because it is easily felt compared to others in your body.

The wrist is a sensitive area that makes bloodshed more uncomfortable compared to a vein near your elbow. The arteries are also deeper than the veins, which increases discomfort.

Pulse oximeter

A pulse oximeter (pulse ox) is a non-invasive device that measures the amount of oxygen in the blood. He does this by sending infrared light to the capillaries with his finger, toe or earlobe. Then it measures how much light is reflected from the gases.

Reading indicates what percentage of your blood is saturated. This test has a 2 percent error window. This means that the reading may be 2% higher or lower than your actual blood oxygen level. This test may be a little less accurate, but it’s very easy for doctors to do. Therefore, doctors rely on this for quick readings.

Things like dark nail polish or cold extremities can cause the ox pulse to read below normal. Your doctor may remove any nail polish before using the machine or if your reading seems abnormally low.

Since the ox pulse is non-invasive, you can do this test yourself. You can purchase pulse wolf devices at most stores that have health products or online. Before using your home device, talk with your doctor so that you understand how to interpret the results.

Where the blood oxygen level should drop

The measurement of oxygen in the blood is called the level of oxygen saturation. In medical abbreviated form you can hear what he called your PaO 2 on blood gas, and O 2 sat while using a pulse. These guidelines will help you understand what your outcome may mean:

Normal: Normal ABG oxygen levels for healthy lungs fall between 80 and 100 millimeters of mercury (mmHg). If ox pulse measures the level of oxygen in the blood, the normal reading is usually between 95 and 100 percent.

However, with COPD or other lung diseases, these ranges may not apply. Your doctor will tell you what is normal for your particular condition. For example, for people with severe COPD, it is often possible to maintain a blood pulse level of 88 to 92 percent.

Below normal: Below normal oxygen levels are called hypoxemia. Hypoxia is often a concern. The lower the oxygen level, the more severe hypoxemia. This can lead to complications in the tissues and organs of the body.

Usually PaO 2 below 80 mmHg. Art. Or pulse ox below 95 percent is considered low. It is important to know what is normal for you, especially if you have a chronic lung disease. Your doctor may recommend which ranges of oxygen levels are acceptable to you.

Above normal: If your breathing is not supported, it is too difficult for your oxygen level. In most cases, high oxygen levels are observed in people who use additional oxygen. This can be found on ABG.

What happens if your oxygen level is too low

When blood oxygen levels go beyond a typical range, you may begin to experience symptoms.

It includes:

  • dyspnea
  • chest pain
  • confusion
  • headache
  • fast heartbeat

If you have low levels of oxygen in the blood, you may show symptoms of cyanosis. A characteristic feature of this condition is the blue discoloration of your nail beds, skin and mucous membranes.

Cyanosis is considered an emergency. If you experience symptoms, you should consult a doctor immediately. Cyanosis can lead to respiratory failure, which can be life threatening.

How to adjust the level of oxygen in the blood

If your blood oxygen level is too low, you may need to increase your oxygen saturation. This is often done with extra oxygen. Home-made supplemental oxygen is considered a medicine and should be prescribed by your doctor. It is important to follow your doctor's recommendations on how to use home oxygen to avoid complications. Your health insurance may cover the costs.

What causes blood oxygen levels to be low

Conditions that can negatively affect your blood oxygen levels include:

  • COPD (including chronic bronchitis and emphysema)
  • Acute Respiratory Distress Syndrome
  • asthma
  • destroyed lung
  • anemia
  • congenital heart defects
  • heart disease
  • pulmonary embolism

These conditions can prevent your lungs from adequately breathing in oxygen-containing air and exhaling carbon dioxide. Likewise, blood disorders and problems with your circulatory system can prevent your blood from collecting oxygen and transporting it throughout the body.

Any of these problems or disorders can lead to a decrease in oxygen saturation. As oxygen levels drop, you may begin to experience symptoms of hypoxemia.

People who smoke may have an inaccurately high heart rate. Smoking causes carbon monoxide to build up in the blood. The impulse ox cannot distinguish this other type of gas and oxygen. If you need to know your blood oxygen level and be a smoker, ABG may be the only way to get an accurate reading.

Check out: What are the first line treatments for treating COPD? "

Bottom line

Most people should not regularly monitor their blood oxygen levels. Only people with health problems that cause low oxygen levels are usually asked to check their levels. Even then, the less invasive pulse oximetry method is often as useful as the invasive ABG.

Despite the fact that it has an error, the readings of pulsed ox are usually quite accurate. If your doctor requires a more accurate measurement, they can take the ABG test.

How pulse oximetry works

Pulse oximetry is performed using a pulse oximeter. The pulse oximeter is a non-invasive means of measuring both the pulse rate and the saturation of arterial hemoglobin with oxygen at the peripheral capillary level. It consists of a portable monitor and a photoelectric probe that is mounted on the finger, finger or toe, or on the patient’s earlobe. The probe measures the amount of red in the capillary during systole and diastole. The monitor calculates the time between peaks and shows the pulse rate in beats per minute. The device also calculates the value based on the light absorption coefficient of systole and diastole and shows the peripheral percentage of oxygen saturation (SpO2).

If the pulse oximeter shows a saturation below 92%, then this is cause for concern. Its fall below 90% suggests hypoxemia. This means that the oxygen concentration in the bloodstream is lower than in the cells. This makes it difficult for oxygen to diffuse from the cells and back into the bloodstream, leading to tissue hypoxia and further to death. A saturation of 94-99% is ideal, but you should keep in mind the factors that can affect the readings of the pulse oximeter. Poor peripheral perfusion, including that caused by shock, vasoconstriction (narrowing of blood vessels), hypotension (low blood pressure), can be noted among the conditions that can make the instrument readings unreliable. Do not attach a sensitive probe to a damaged limb. Do not use the device on the same hand on which blood pressure is measured. It should be borne in mind that the readings of the pulse oximeter will go down at a time when the cuff of the tonometer is inflated. It will block the arterial blood flow, which affects the readings,

Changes in the field of medicine, as well as related electronic portable devices, can be called truly revolutionary. Instruments that used to be found only in hospitals are now available for home medical use. A good example is an oxygen concentrator for the home. Accordingly, pulse oximeters are used by nurses in hospitals, ambulatory patients at home, fitness enthusiasts in the gym, and even pilots on airplanes. Pulse oximetry is the most informative method for determining oxygen to blood levels.

Pulse oximetry. Degrees of oxygen deficiency relative to saturation (SpO2) - pulse oximeter readings

Power SpO2,% (Pulse oximetry readings)
Normmore than or equal to 95%
1 degree90-94%
2 degree75-89%
3 degreeless than 75%
Hypoxemic comaless than 60%

Recommendations, the necessary flow of oxygen, the regimen and duration of oxygen therapy, are prescribed by the attending physician! Oxygen therapy at home is carried out using oxygen concentrators under the control of a pulse oximeter.