What is spo2 in medicine. What is oxygen saturation? Errors when performing pulse oximetry

One of the most important needs of the human body is a continuous supply of oxygen. And this applies not only to the air entering the lungs by inhalation through the nose or mouth, but also to the supply of oxygen to all organs and tissues of the body. If oxygen stops flowing into every cell of the body, a person will live only a few minutes.

What is saturation

The protein responsible for transporting oxygen throughout the body is hemoglobin, which is found in red blood cells - erythrocytes. One molecule of hemoglobin can carry 4 molecules of oxygen, if this happens in the human body, then the saturation level is 100%, but this practically never happens. To put it in a more understandable language, the saturation of a liquid, that is, blood, with gases, that is, oxygen, is saturation.

In medicine, saturation is measured using the so-called saturation index - an average percentage determined using pulse oximetry. A special saturation sensor is a pulse oximeter, which is available in every hospital, and today it can be purchased for use at home. The saturation - Spo2 and pulse rate - HR are shown on his monitor. If the saturation indicators are normal, they simply appear on the screen and are accompanied by a smooth sound signal, and when the patient has a decrease in saturation, no pulse, or vice versa - tachycardia, the saturation measuring device will sound an alarm signal. Most often, low respiratory saturation or respiratory failure occurs with pneumonia (severe), chronic obstructive pulmonary disease, coma, apnea, and also in extremely premature babies.

Determination of saturation is necessary in order to timely identify deviations of this indicator from the norm and avoid complications that may result from insufficient saturation of hemoglobin with oxygen.

How to determine the degree of respiratory failure by saturation

Normal lung saturation is the same in the elderly, adults, children and newborns, and it is 95% - 98%. Lung saturation below 90% is an indication for oxygen therapy. You can determine saturation with two types of pulse oximeter - transmission or refractive. The first one measures oxygen saturation using a sensor that is attached to the pad of the finger, earlobe, etc., the second one can determine this indicator in almost any part of the body. The accuracy of both devices is the same, but reflected pulse oximetry is more convenient to use. Saturation can be compared with partial pressure:

• SpO2 from 95% to 98% corresponds to PaO2 at the level of 80-100 Hg;
• SpO2 from 90% to 95% corresponds to PaO2 at the level of 60-80 Hg;
• SpO2 from 75% to 90% corresponds to PaO2 at the level of 40-60 Hg;

Very often the saturation drops in premature babies. As medical practice has shown, the mortality rate among premature babies with low saturation is higher than the mortality rate among children with saturation levels that are within the normal range.

In many diseases and emergencies, oxygen saturation in the blood is measured; the norm is 96-99%. In the general sense, saturation is the saturation of any liquid with gases. The medical concept includes the saturation of blood with oxygen. When it decreases, the human condition worsens, since this element is involved in all metabolic processes. An integral part of the treatment of such diseases is to increase its level through the use of an oxygen mask or pillow.

More about saturation

Using scientific data, we can say that the determination of blood oxygen saturation occurs by the ratio of bound hemoglobin to its total amount.

Providing the body with various substances and elements occurs thanks to a complex system of absorption of the necessary components. The delivery of necessary substances and the removal of unnecessary substances is organized through the circulatory system, in the small and large circles.

The process of saturating the blood with oxygen is ensured by the lungs, which conduct air through the respiratory system. It contains 18% oxygen, warms up in the nasal cavity, then passes through the pharynx, trachea, bronchi, and later enters the lungs. The structure of the organ includes alveoli, where gas exchange occurs.

The saturation process occurs according to the following chain:

1. A complex system of capillaries and venules surrounding the alveoli transfers gases from the air into the bubbles (alveoli).
2. The venous blood that comes here, poor in oxygen, goes in a large circle, diverging to organs and tissues. Carbon dioxide from the alveoli passes back into the respiratory organs and is released out.
3. The transfer of oxygen molecules occurs with the help of hemoglobin, which is contained in red blood cells.

Hemoglobin contains iron (4 atoms), so one protein molecule is capable of attaching 4 oxygens.

Reasons for the decline

If the oxygen saturation in the blood differs from the norm (the normal value is 96-99%), this may occur for the following reasons:

• the number of oxygen-carrying cells (erythrocytes, hemoglobin) decreases;
• the process of oxygen transfer to the alveoli is disrupted;
• the ability of the heart to pump blood into the vessels or transport it through the circulation changes.

People may experience similar difficulties due to a global environmental problem. In large cities where there are operating industrial enterprises, the issue of increasing the level of exhaust gases in the air is often raised.

Because of this, the oxygen concentration decreases, hemoglobin carries molecules of poisonous gases, causing slow intoxication.

In practice, these disorders manifest themselves as the following diseases:

• anemia;
• autoimmune diseases;
• chronic respiratory tract processes (pneumonia, bronchitis);
• obstructive diseases (cystic fibrosis, bronchial asthma);
• heart failure (heart defects, chronic congestion).

Saturation measurement occurs during operations and during the administration of anesthesia, as well as if monitoring the condition of premature newborns is necessary.

Lack of oxygen has certain signs; they are associated with a violation of its proportion with carbon dioxide. The opposite situation may also occur when the gas supply is excessive. This is also bad for the body because it causes intoxication. This situation occurs in the case of a long stay in the fresh air after prolonged oxygen starvation.

The likelihood of getting a decrease in saturation depends on a person’s lifestyle. The less time he spends in the fresh air, the greater the chance of pathology.

Parameter Definition

Determining oxygen content is a simple procedure; it can be carried out using several methods, after blood sampling or without it at all:

1. A non-invasive research method involves using a device whose electrode is placed on a finger or belt, and within a minute the result is recorded. The instrument is called a pulse oximeter, and allows you to quickly conduct a test in a safe way.
2. If you use an invasive method, arterial blood is collected, but in this case it takes a lot of time to get results.

The principle of operation of a pulse oximeter is that the liquid medium of the body with varying degrees of oxygen saturation differs not only in color, but also in the level of absorption of infrared waves. In arterial, that is, saturated blood, infrared waves are absorbed, and in venous blood, red waves are absorbed. Therefore, the pulse oximeter records data from both blood flows and, based on them, calculates the saturation indicator.

Devices can be stationary or portable, and if older devices are available in a hospital, then in an emergency setting it was not previously possible to determine oxygen saturation. They had a lot of positive aspects: a large number of sensors, memory capacity, and the ability to print results. The invention of a portable device made it possible to quickly navigate an emergency situation. Modern devices can record results around the clock, turning on when the patient is active.

An overnight pulse oximeter takes measurements when a person wakes up. Almost all types of pulse oximeters are available in various price categories, depending on the capabilities and needs of the buyer.

The following manifestations are characteristic of a saturation disorder:

1. Decreased human activity, increased fatigue.
2. Dizziness, weakness, drowsiness.
3. The appearance of shortness of breath.
4. Reduced blood pressure.

If there is excessive saturation of the blood with oxygen, then signs of this phenomenon include headache and heaviness. At the same time, symptoms similar to low blood oxygen saturation may occur.

Treatment

If the blood cannot be saturated with oxygen, then it is necessary to find the cause of this phenomenon and eliminate it, and then enrich the liquid medium with gas. You need to start worrying already when the oxygen content is below 95%.

Here is the sequence of the treatment plan:

1. Many conditions in which saturation decreases are complex and advanced, so treatment of the underlying disease is a difficult task.
2. In this regard, increasing the ability of the blood to be saturated with oxygen in a natural way is difficult. Treatment of low saturation occurs by prescribing its inhalation through a mask or inhalation of an oxygen cushion.
3. As a rule, this happens in a hospital setting, so oxygen therapy is performed during the period of exacerbation of the pathology.

If the oxygen level is slightly reduced, then correction of the condition is possible by increasing walks in the fresh air.

Thank you

The site provides reference information for informational purposes only. Diagnosis and treatment of diseases must be carried out under the supervision of a specialist. All drugs have contraindications. Consultation with a specialist is required!

What is pulse oximetry?

• Under anesthesia. During the operation, the patient is unconscious and cannot complain about the deterioration of his condition. Pulse oximetry provides objective data without his participation. The anesthesiologist can monitor the depth of anesthesia and, if necessary, support vital processes. This is especially important during complex and risky operations.
• During operations on the limbs. Surgeries on the extremities are often accompanied by temporary blockage of blood vessels to prevent severe bleeding. A pulse oximeter is attached to your finger and allows you to monitor blood circulation. Too little oxygen saturation can lead to tissue death, causing complications.
• When transporting patients. A regular pulse oximeter is portable and does not take up much space, so it is convenient to use for monitoring the condition of patients during their transportation. Many ambulances, airplanes and medical helicopters are equipped with pulse oximeters.
• In reanimation. In the postoperative period and in case of severe life-threatening illnesses, patients are in intensive care. Pulse oximetry in these departments is carried out continuously ( for several days or more). In addition, devices are used to alert medical personnel when a patient's vital signs decrease.
• For some diseases of the lungs and heart. In a number of lung pathologies and heart diseases, problems arise with oxygen saturation in the body. Pulse oximetry helps determine the severity of the disease and choose the right treatment tactics. In addition, it can be used to quickly diagnose attacks of bronchial asthma, sleep apnea ( respiratory arrest) and other pathologies that manifest themselves in the form of attacks.
• For carbon monoxide poisoning and treatment with oxygen. For a number of diseases, patients are prescribed treatment with a mixture of gases with a high oxygen content ( the mixture is inhaled through a mask). This allows you to quickly increase the concentration of oxygen in the blood. Pulse oximetry determines the effectiveness of such treatment and allows you to understand when the patient's condition will return to normal.
• When preparing athletes. In this case, pulse oximetry is not performed for medical reasons. Professional athletes are healthy, but this study allows us to improve the quality of their training. Trainers and doctors monitor blood oxygen saturation during extreme loads and make the necessary adjustments in training methods.

What indicators does pulse oximetry reflect? ( saturation, SpO2, etc.)

The indicators recorded by pulse oximeters have the following features:

• Blood oxygen saturation. The saturation of peripheral blood with oxygen is also called saturation and is designated SpO2. This indicator is very important, as it indicates problems with breathing and cardiac activity almost immediately ( in the process of verification), before indirect signs of oxygen deficiency appear - turning blue ( cyanosis) skin and mucous membranes, changes in heart rate, subjective discomfort in the patient.
• Pulse rate. The pulse rate reflects the heart rate, but does not always coincide with it one hundred percent ( that is, electrocardiography and pulse oximetry data may differ). This is explained by the different elasticity of the vessels, the ability of their walls to partially absorb pulsation, and possible blockage of the lumen of the vessel. However, a pulse oximeter in any case indirectly reflects the work of the heart and helps to suspect certain disorders. To reliably determine the pulse rate during pulse oximetry, the device must correctly read the data for at least 15 to 20 seconds.

Pulse oximeters used in hospital settings ( intensive care unit, operating room, etc.) are often “built-in” into more complex devices and equipped with a wider range of functions. They record the same indicators, but in combination with other devices, computers provide more complete information about the patient’s condition ( pulse filling, breathing rate, etc.).

Norm of pulse oximetry in adults, children and newborns

Normal heart rate at different ages:

• newborns and children under 2 years old - 110 - 180 beats per minute;
• children 2 – 10 years old – 70 – 140 beats per minute;
• teenagers ( over 10 years old) and adults – 60 – 90 beats per minute.

Normal arterial blood oxygen saturation should always be above 95%. Lower rates are typical for various diseases, and the lower the rate, the more severe the patient’s condition. Blood oxygen saturation of less than 90% is considered life-threatening and such patients require urgent medical attention.

Oxygen saturation of venous blood is measured much less frequently and does not have such great practical significance. Its norm is 75% and above.

Which doctor prescribes and performs pulse oximetry?

The following doctors usually prescribe pulse oximetry:

• anesthesiologists ( sign up) ;
• resuscitators;
• pulmonologists ( sign up) ;
• phthisiatricians ( sign up) ;
• surgeons ( sign up) ;
• therapists ( sign up) and etc.

Carrying out pulse oximetry does not require special skills or special training. Typically, nurses and nursing staff are familiar with the instructions and prepare the patient and equipment. The doctor can conduct the study independently if there is a risk of rapid deterioration of the condition. For example, in the operating room, an anesthesiologist monitors the pulse oximeter readings.

Do I need special patient preparation before pulse oximetry?

The conditional preparation of a patient for pulse oximetry includes the following recommendations:

• Do not use stimulants. Any stimulants ( narcotic drugs, caffeine, energy drinks) affect the functioning of the nervous system and internal organs. If taken before the procedure, pulse oximetry will provide objective information, but the body's condition will change as the effect of the stimulants wears off.
• To give up smoking. Smoking immediately before the procedure can affect the depth of inspiration, heart rate, and vascular tone. These changes will lead to a decrease in blood oxygen saturation, which will be reflected by pulse oximetry.
• Quitting alcohol. A single dose of alcohol will not significantly distort pulse oximetry data. But if the patient regularly drank alcohol a few days before the procedure, this will affect liver function. The liver is responsible for producing many blood components and enzymes. Thus, the pulse oximetry result will be somewhat distorted.
• Do not use hand creams or nail polish. In most cases, the pulse oximeter sensor is attached to the finger. Using different hand creams can affect the "transparency" of the skin. The light waves that are supposed to detect oxygen saturation in the blood may encounter an obstacle, which will affect the test result. Nail polishes ( especially blue and purple colors) and completely make the finger impenetrable to light, and the device will not work.
• Eat as usual. Overeating or fasting on the eve of the test may somewhat distort the results, as more of certain substances will appear in the blood. It is best to eat as usual before the test so that the result can be interpreted as the normal state of the body.

Is it painful to do pulse oximetry?

Thus, the patient is in a comfortable position and does not experience pain or any discomfort. This allows pulse oximetry to be performed even on small children and newborns. For them, there are special designs of sensors with soft pads so that the sensor does not rub delicate skin even during long-term examination.

How long does pulse oximetry take?

Monitoring is more often used ( observation) the patient's condition over a long period of time. The pulse oximeter records data on how the patient's vital signs changed during the night, day or under certain conditions.

The procedure may last several hours or more in the following cases:

• during surgery;
• during patient transportation;
• in the postoperative period or in critically ill patients in intensive care;
• all night if necessary to detect attacks of sleep apnea ( respiratory arrest);
• during an attack of bronchial asthma to objectively determine the severity of the disease;
• for 24 hours or more to record attacks of other diseases ( at the discretion of the attending physician).

Is it possible to perform pulse oximetry yourself at home?

To obtain reliable data, the patient only needs to follow the instructions in the instructions for the device. If the patient has additional questions regarding the interpretation of the results, it is better to consult a specialist. If the pulse oximeter at home gives saturation ( oxygen saturation) less than 95%, you should immediately consult a doctor.

What kind of device is a pulse oximeter?

To obtain reliable results when using a pulse oximeter, you must adhere to the following recommendations:

• Correct choice of study site. It is advisable to perform pulse oximetry in a room with moderate lighting. Then the bright light will not affect the operation of the light-sensitive sensors. Intense light ( especially red, blue and other colors) can significantly distort the results of the study.

• Correct positioning of the patient. The main requirement during pulse oximetry is the patient's static position. It is advisable to carry out the procedure while lying on the couch with a minimum amount of movement. Fast and sudden movements can lead to displacement of the sensor, deterioration of its contact with the body and distortion of the result.
• Turning on and powering the device. Some modern pulse oximeters turn on automatically after putting on the sensor. In other models, the device must be turned on independently. In any case, before using the pulse oximeter, you need to check the charge level ( for rechargeable or battery-powered models). The study can take quite a long time, depending on the information the doctor wants to obtain. If the device is discharged before the procedure is completed, it will have to be repeated.
• Attaching the sensor. The pulse oximeter sensor is attached to the part of the body specified in the instructions. In any case, it must hold well so as not to accidentally fall when the patient moves. Also, the sensor should not pinch your finger or tighten your wrist too much.
• Correct interpretation of results. The pulse oximeter provides results in a form that is understandable to the patient. This is usually your heart rate and blood oxygen saturation level. However, only the attending physician can correctly interpret the result. He compares the results with the results of other studies and the patient's condition.

Currently, almost every patient can purchase portable pulse oximeters at home. It is better to coordinate this purchase with your doctor. It is not always necessary. More often, these devices are purchased for treating or caring for seriously ill people at home. A pulse oximeter may also be needed if there are difficulties in transporting the patient. Most modern ambulances are equipped with special models.

What types of pulse oximeters are there?

The main advantages that are found in different models of pulse oximeters are:

• Indication of normal limits. Most modern pulse oximeters themselves can determine the normal limit. It is reflected on the screen next to the patient’s indicators. In some cases, the numbers on the screen may turn red if your vital signs are falling.
• Sound signal. Some devices are equipped with a special sensor that reacts to a decrease in blood oxygen saturation and notifies about this by giving a sound signal. This allows doctors to quickly respond to the problem.
• Portability. Pulse oximeters can be stationary ( for hospitals) and portable ( for home use and ambulances).
• Data processing. Most pulse oximeters display data in the form of numbers on the monitor. However, some can print out a graph of changes over time, which is very useful in the case of a long study.
• Compatible with other devices. Pulse oximeters used in critical care settings in hospitals are built into or can be connected to more complex life support machines. “Home” portable devices do not have such a function.

Pulse oximeter sensors ( finger, adult, child, etc.)

All pulse oximeter sensors are connected by a flexible wire to the pulse oximeter itself. Here the data is processed and presented in a convenient form ( usually on the screen in the form of numbers or a graph).

There are the following types of sensors for pulse oximetry:

• Clips. Such sensors resemble a clothespin in shape, which is usually fixed on the patient’s index finger or earlobe. This type is well suited for adults and adolescents when the patient is observed for a short time. Wear the clip if you need long-term measurements ( several hours or more) is inconvenient, since it can move during movements, distorting the results of the study.
• Flexible silicone sensors. Such sensors are more often used when performing procedures in newborns. They are usually attached to the side of the leg, since the toes are too small for testing and it is difficult to fix the sensor well on them. In addition, silicone attachments do not cause discomfort to the child.
• Silicone sensors for adults. Such sensors are used when long-term monitoring is required ( more than 3 – 4 hours). They fit well and do not cause inconvenience or discomfort. Depending on the model, the sensor may be designed for a certain finger diameter ( for example, the instructions indicate - with a finger thickness from 9 to 12 mm). This parameter cannot be neglected, since otherwise the device will not illuminate the thickness of the tissue of the finger, and the result of the study will be distorted.
• Ear clip. Such sensors differ in shape from finger clips. As a rule, they have convenient latches ( like an earphone), allowing them to be firmly attached to the auricle. The light elements are positioned so as to illuminate the earlobe. Ear clips are used for long-term studies when the patient is engaged in everyday activities, and it is simply not possible to attach the clip to a finger.

Some clinics use disposable pulse oximetry sensors, which is more hygienic for patients. There is no fundamental difference in obtaining results. Disposable sensors are manufactured separately for each device model.

Where can I attach the pulse oximeter sensor?

In the case of reflected pulse oximetry, there are more possibilities, since the sensors can be attached to a flat area of ​​​​the skin. Doctors often place such sensors on the extremities where there are difficulties with blood circulation. In other words, the site of attachment can be almost anywhere, provided that there is a good vascular network there.

Technique, principle and algorithm of pulse oximetry

The amount of oxygen in the blood is measured as follows. In red blood cells ( red blood cells) contains hemoglobin, a substance capable of attaching oxygen atoms.
In a healthy body, one hemoglobin molecule is capable of attaching 4 oxygen molecules. In this form, it spreads to organs and tissues with arterial blood. In venous blood, the amount of dissolved oxygen is less, since some of the hemoglobin molecules are “busy” transferring carbon dioxide from the tissues to the lungs.

Pulse oximetry uses the method of selective absorption of light waves to determine the amount of oxygen attached to hemoglobin in arterial blood ( in the form of oxyhemoglobin). To do this, the tissues are “translucent” so that the waves are absorbed by capillaries. The most accurate data, accordingly, will be in those areas where the circulatory network is denser.

The pulse oximetry technique includes the following steps:

• the patient is “prepared” for the procedure, explaining what will happen and how;
• on a finger, earlobe or other part of the body ( of necessity) install the sensor;
• the device is turned on, and the measurement process itself begins, which lasts at least 20 - 30 seconds;
• The device displays the measurement result on the monitor in a form convenient for the doctor or patient.

What is fetal pulse oximetry?

This research method is used in neonatology and obstetrics. To carry it out, special equipment is required, which not all clinics have. Fetal pulse oximetry may be needed for some pregnancy complications, birth defects and other problems.

Errors when performing pulse oximetry

The most common mistakes made when performing pulse oximetry are:

• presence of nail polish;
• incorrect sensor attachment ( weak fixation, poor contact with tissues);
• some blood diseases ( which were not known before the start of the study);
• patient movements during the study;
• using sensors of the wrong model ( by age, weight, etc.).

Interpretation and interpretation of pulse oximetry results

Types and methods of pulse oximetry

Computer pulse oximetry

• Ability to save data. The computer is able to store in memory information about measurements over a certain period of time. This is necessary, for example, for daily pulse oximetry. In addition, the computer can build graphs based on the stored data.
• Removing artifacts. Artifacts in pulse oximetry are distortions that can appear when the sensor is improperly secured and a number of other errors. Some devices can distinguish such distortions and automatically make adjustments to the received data.
• Alarm function. The computer stores data on the normal saturation and heart rate. If the patient’s indicators decrease significantly, the pulse oximeter will notify you with a special signal. Such models are very convenient for intensive care units or operating rooms where patients are in serious condition.
• Compatible with other devices. The computer allows you to connect the pulse oximeter to other medical devices, which may be necessary for more complex diagnostic tests.

Transmission pulse oximetry

Transmission pulse oximetry has become widespread, primarily due to the relatively low cost of the device and the ease of conducting the study. All models of pulse oximeters intended for home use are based on the principle of transmission pulse oximetry.

Reflected pulse oximetry

It is most convenient to resort to reflected pulse oximetry in the following cases:

• with long-term observation of the patient;
• in pediatrics and neonatology ( since it is difficult to explain to children that they should not move suddenly);
• in the diagnosis of diseases of certain organs ( the sensor is fixed in the area of ​​the organ and indirect data on blood circulation is obtained);
• in fitness centers and in the training of professional athletes.

Reflected pulse oximetry has several disadvantages:

• Possibility of allergy to the adhesive ( sometimes the sensor is glued to the skin during the procedure);
• poor contact with skin if the sensor was poorly secured;
• the appearance of significant distortions in case of severe tissue swelling;
• The sensor cannot be attached to the skin in case of some dermatological diseases.

Overnight pulse oximetry ( respiratory night monitoring)

Night pulse oximetry is almost always carried out in specialized departments by somnologists. They not only monitor the correct execution of the procedure ( correct position of the sensor on the finger), but also provide the necessary assistance if there is a threat to the patient’s health.

Daily pulse oximetry

Daily pulse oximetry can detect disturbances in the functioning of the following organs and systems:

• respiratory system ( lungs, trachea, etc.);
• the cardiovascular system ( heart, vessels of the pulmonary and systemic circulation);
• hematopoietic system ( low level of red blood cells, their pathological changes);
• some metabolic diseases.

Non-invasive pulse oximetry

Non-invasive pulse oximetry has the following undoubted advantages over invasive:

• the procedure does not require special training or even medical education;
• quickly gives results in real time ( monitoring takes place);
• the procedure is cheap and accessible, as it does not require expensive equipment;
• The patient can be observed at home or during transportation;
• the procedure can continuously last for several hours or even days;
• there is no risk of complications or infection of the patient, since there is no direct contact with blood;
• the procedure does not require special preparation of the patient.

Invasive pulse oximetry

Sensor installation location ( vessel) may be different. The limiting factor is the diameter of the artery, since even with the sensor inserted, blood must circulate freely through this vessel. Also, the injection site is chosen depending on the specific pathology or problem ( for example, in an area where, for one reason or another, blood oxygen saturation is reduced). In some cases, sensors are also inserted into large veins.

Most often, sensors for invasive pulse oximetry are placed in the following vessels:

• radial artery;
• femoral artery;
• the veins of the arms and legs are quite large in diameter.

Currently, invasive pulse oximetry is used exclusively in intensive care or surgical settings ( of necessity). Sometimes this method is used in research institutes to obtain more accurate data. In ordinary hospital settings, minor errors in non-invasive pulse oximetry do not play a significant role, and the use of an invasive method is simply not justified.

Indications and contraindications for pulse oximetry

What diseases require pulse oximetry?

However, there is a certain range of diseases for which pulse oximetry is a very important diagnostic method. We are talking about pathologies of the cardiovascular and respiratory systems. The fact is that these systems are mainly responsible for saturating the body with oxygen. Accordingly, problems with the heart or lungs more often and faster than other diseases lead to a decrease in the concentration of oxygen in the blood.

Most often, pulse oximetry is performed for the following pathologies:

• respiratory failure ( against the background of various diseases);
• bronchial asthma;
• sleep apnea syndrome;
• carbon monoxide poisoning.

During respiratory ( respiratory) insufficiency

Depending on the degree of oxygen saturation of the blood, the following types of respiratory failure are distinguished:

• Compensated. In case of compensated respiratory failure, pulse oximetry readings will be within normal limits. Other organs are coping with minor breathing problems, and blood oxygen levels will drop slightly.
• Decompensated. In decompensated respiratory failure, pulse oximetry will detect a significant decrease in blood oxygen levels. This is an indication for a more intensive treatment regimen ( artificial ventilation, etc.).

For COPD ( chronic obstructive pulmonary disease)

For pneumonia ( pneumonia)

For bronchial asthma

For carbon monoxide poisoning

For sleep apnea

Contraindications to pulse oximetry

The only significant contraindication is psychomotor agitation, when, due to nervous or mental disorders, the patient is not aware of what is happening. In this case, it is simply not possible to secure the sensor, because the patient himself tears it off. However, the use of tranquilizers helps to calm the patient and carry out the procedure. A similar situation may occur during convulsions, when, due to severe trembling in the limbs, the sensor will move, and it is more difficult to obtain reliable data.

What tests and examinations are done with pulse oximetry?

• capnometry;

Spirometry

Capnometry

Peak flowmetry

Where to do pulse oximetry?

Sign up for pulse oximetry

To make an appointment with a doctor or diagnostics, you just need to call a single phone number
+7 495 488-20-52 in Moscow

+7 812 416-38-96 in St. Petersburg

The operator will listen to you and redirect the call to the desired clinic, or accept an order for an appointment with the specialist you need.

In St. Petersburg

Slight fluctuations in blood oxygen saturation levels can occur in every person. For a more accurate analysis of changes in this indicator, it would be correct to carry out several measurements. Further in the article we will find out why fluctuations occur, how they are recorded and why they need to be controlled.

Decrease in O2 level in the blood: causes

Oxygen saturation of the blood occurs in the lungs. Then O2 is carried to the organs with the participation of hemoglobin. This compound is a special carrier protein. It is found in erythrocytes - red blood cells. By the level of oxygen saturation, you can determine the amount of hemoglobin that is present in the body in an oxygen-bound state. Ideally, the saturation level should be between 96-99%. With this indicator, almost all hemoglobin is associated with oxygen. The reason for its decrease may be severe forms of diseases of the respiratory and cardiovascular systems. With anemia it decreases significantly. In case of exacerbation of chronic heart and pulmonary diseases, a decrease in oxygen in the blood is also observed, so it is recommended to immediately consult a doctor.

Colds, flu, ARVI, pneumonia, chronic bronchitis affect this indicator and report a severe form of the disease. During the examination, it is necessary to take into account some extraneous factors that affect the decrease in oxygen saturation in the blood and change the indicators. These include movement of the hands or trembling of the fingers, manicure with dark-colored varnish, direct exposure to light. Factors that should also be noted are low room temperature and nearby objects with electromagnetic radiation, including a mobile phone. All this leads to errors in measurements during diagnosis.

Saturation - what is it?

This term refers to the state of saturation of liquids with gases. Saturation in medicine refers to the percentage of oxygen contained in the blood. This indicator is one of the most important and ensures the normal functioning of the body. Blood carries the oxygen necessary for proper functioning to all organs. How to determine what saturation is in the blood? What will it give?

Pulse oximeter

Blood oxygen saturation is determined by a method called pulse oximetry. The device used for this is called a pulse oximeter. For the first time, this technique was used in medical institutions in wards. The pulse oximeter became a publicly available tool for diagnosing human health. They began to use it even at home. The device is easy to use, so it measures some vital indicators, including pulse and saturation. What kind of device is this and how does it function?

Operating principle of the equipment

The circulation of a significant amount of oxygen in the body occurs in a state bound to hemoglobin. The rest of it is freely distributed by blood, which is capable of absorbing light and any other substances. What is the principle of operation of a pulse oximeter? To carry out the analysis, it is necessary to take a blood sample. As you know, many people do not tolerate this unpleasant procedure well. This is especially true for children. It is quite difficult for them to explain why saturation is determined, what it is and what the need is for it. But, fortunately, pulse oxometry eliminates such troubles. The examination is carried out completely painlessly, quickly and absolutely “bloodlessly”. An external sensor that is connected to the device is placed against the ear, fingertip, or other peripheral organs. The result is processed by the processor and the display shows whether the oxygen saturation is normal or not.

Peculiarities

However, there are a couple of nuances. In the human body, there are two types: reduced and oxyhemoglobin. The latter saturates tissues with oxygen. The job of a pulse oximeter is to distinguish between these types of oxygen. The peripheral sensor contains two LEDs. Red light rays, having a wavelength of 660 Nm, come from one, and infrared light rays, whose wavelength is 910 Nm and higher, come from the other. It is because of the absorption of these fluctuations that it becomes possible to determine the level of oxyhemoglobin. The peripheral sensor is equipped with a photodetector, which receives light rays. They pass through the tissue and send a signal to the process block. Next, the measurement result is displayed on the display, and here you can determine whether the oxygen saturation is normal or there are deviations. The second nuance is the absorption of light only from this. This occurs due to its ability to change its density, doing this simultaneously with changes in blood pressure. As a result, arterial blood fluctuates significantly more. A pulse oximeter detects light passing through the artery.

Determination of saturation (saturation) of venous blood with oxygen (SvO 2) is one of the modern areas of invasive monitoring. This parameter is compared to the “watchdog” of oxygen balance and is sometimes called the “fifth vital indicator”, which allows us to indirectly judge the global balance between oxygen delivery and consumption. It should be remembered that periodic or continuous measurement of DM and SaO 2 (SpO2 ) makes it possible to track delivery O 2 , but at the same time says nothing about the need in it, within the framework of the hierarchical feedback described by Pflüger E.F., “need - consumption - delivery”.
Oxygen consumption can be calculated according to Fick's principle:

VO 2 = CB × (CaO 2 – CvO 2)

By mathematically transforming this equation, it can be determined that for a given VO 2 value, SvO 2 is proportional to the relationship between oxygen supply and oxygen demand:

SvO 2 ~ SaO 2 – ~ SaO 2 – (VO 2 / SV),

Where SvO 2 – saturation (saturation) of venous blood with oxygen (%); SaO 2 – arterial blood oxygen saturation (%); Hb – hemoglobin concentration (g/l); VO 2 – oxygen consumption by tissues (ml/min); CO – cardiac output (l/min).

Thus, the saturation of hemoglobin in venous blood with oxygen will be proportional to the average value of O 2 extraction (VO 2 /DO 2, O 2 ER) and, if reduced, may be a consequence of a critical imbalance between oxygen delivery and the need for it. Studies have shown that, when compared with ADMV and HR values, SvO 2 shows the clearest relationship with O 2 ER.
Indeed, perfusion blood pressure, although the most frequently measured hemodynamic indicator, has the least significance in assessing the adequacy of oxygen transport and tissue oxygenation. Despite the normalization of blood pressure and CO, inadequate distribution of blood flow or blockade of O2 consumption may be accompanied by tissue hypoxia and progression of MODS.
The classic point for measuring venous saturation (SvO 2) is the pulmonary artery, which contains mixed venous blood from the basin of the inferior and superior vena cava, as well as the coronary sinus. Accordingly, the study of this parameter requires pulmonary artery catheterization. Normal values
indicators can vary in the range of 65–75%. In critical conditions, the interpretation of dynamic changes in SvO 2 is more important than a one-time assessment of its absolute value (Table 1).

Table 1. Mixed venous blood saturation: ranges of values

The SvO 2 indicator gives us the average value of SO 2 of blood flowing from various organs and tissues. However, at the level of a single organ or sector of the body, the saturation of venous blood with oxygen can vary significantly, which is determined by the nature and intensity of the organ’s work (Table 2).
For example, O2 consumption by muscles can increase significantly during physical activity due to an increase in its extraction, which leads to a decrease in SO2 flowing blood.
During physical activity, CvO 2 and SvO 2 values ​​decrease, despite an increase in DO 2 . The SvO 2 indicator for the kidneys is high and amounts to 90–92%. The relatively large volume of renal blood flow is not related to the organ’s own needs and reflects its excretory function.

Table 2. Relative volume of perfusion, oxygen consumption and saturation
oxygenation of venous blood flowing from various organs

It must be taken into account that in critical conditions accompanied by lung damage, there is a clear correlation between changes in SvO 2 (ΔSvO 2) and SaO 2 (ΔSaO 2). In addition to the state of external gas exchange, there are a large number of factors that determine the resulting SvO 2 value. Thus, a decrease in SvO2 can be caused not only by tissue hypoperfusion (decreased CO), but also by arterial desaturation, as well as a decrease in hemoglobin concentration, including as a result of hemodilution during infusion therapy (Table 3).
According to Ho K.M. et al.21 (2008), arterial blood oxygenation (PaO2) can have an even greater impact on the value of venous saturation than the cardiac output value. Thus, the assessment and interpretation of SvO 2 should be based on an integrated approach that takes into account such important determinants as SaO 2, heart rate, blood pressure, central venous pressure, CO, diuresis rate, as well as hemoglobin and lactate concentrations in venous blood. The presence of a large number of factors that determine the resulting SvO 2 value and their rapid change in critical conditions create the prerequisites for continuous monitoring of venous saturation in intensive care and anesthesiology.

Table 3. Reasons for changes in mixed and central venous blood saturation
ScvO 2 – central venous blood saturation; SvO 2 – saturation of mixed venous blood; SV – heart
ny ejection; Hb – hemoglobin concentration; SaO 2 – saturation of arterial blood with oxygen; OPL –
acute lung injury

Despite these limitations, SvO2 assessment remains a useful approach aimed at early detection of shock, in particular its “latent” forms (“cryptic shock”), not manifested by an increase in plasma lactate concentration and signs of extensive multiple organ failure. Diagnostic, prognostic and therapeutic
the poetic significance of a decrease in SvO 2 has been demonstrated in various groups of intensive care patients.28 However, a number of critical conditions can be accompanied by a heterogeneous distribution of perfusion, blood shunting at the precapillary level, disproportionate inhibition of circulation and mitochondrial activity (blockade of oxygen extraction). Against the background of such disorders, in particular with septic shock, an increase in SvO 2 may be observed, which is associated with the suppression of oxygen uptake by cells against the background of mitochondrial dysfunction and microcirculation disorders. It is no coincidence that septic shock is sometimes characterized as “microcirculatory and mitochondrial distress syndrome.”
“Supranormal” SvO2 values, observed in some cases against the background of MODS, should not be considered a sign of excessive oxygen delivery or “excellent perfusion.” On the contrary, an increase in SvO 2 may indicate suppression of mitochondria and “robbing” those areas where the need for oxygen is especially high, with all the ensuing consequences.7 A similar picture is observed when blocking the mitochondrial respiratory chain with cyanide. Often, an increase in SvO 2 can be a consequence of a hyperdynamic circulatory reaction against the background of sepsis, vasodilation and inotropic support.
According to Varpula M. et al.51 (2005), outcome in patients with septic shock was associated with SvO 2 in addition to other variables (ABV, lactate concentration, and central venous pressure), and SvO 2 >70% was associated with improved outcome. However, in the study by Dahn M.S. et al. indicates that in patients with sepsis the hour-
then it is not possible to register a significant decrease in SvO 2, which may be a consequence of regional disturbances in oxygen consumption. In this regard, some authors do not recommend using SvO2 as a marker of tissue hypoperfusion.
In a randomized study, Gattinoni L. et al. an increase in SvO 2 >70% within 5 days in patients with septic shock was not accompanied by a significant decrease in mortality. However, six years later, Rivers E.P. et al. 37 (2001) demonstrated a significant improvement in outcome using a targeted therapy protocol that included a functional analogue of SvO 2 - central venous blood saturation (ScvO 2).

Measurement of central venous blood saturation (ScvO2 )
To discretely measure the saturation of “central” venous blood (ScvO 2), blood sampling from the superior vena cava is required, followed by a study of the gas composition of the sample. Continuous measurement of ScvO 2 requires the installation of a fiber optic sensor and is based on the principle of reflectance photometry.
The main advantage of measuring SсvO 2 compared to SvO 2 is that pulmonary artery catheterization is not required. Indeed, early placement of a Swan-Ganz catheter for initial treatment of shock and MOF may be technically difficult and impractical, while
A venous catheter is placed in most patients admitted to the ICU. It is known that in addition to diagnostic purposes (measurement of central venous pressure and ScvO2), catheterization of the central venous bed is necessary for infusion and renal replacement therapy, parenteral nutrition, as well as the administration of vasopressor and inotropic drugs. It is noteworthy that, according to Bauer P. and Reinhart K., it is the need to measure ScvO 2 that can be considered as a decisive indication for catheterization of the central venous bed in critical conditions.
It should be noted that in 10–30% of cases the tip of the central venous catheter is located in the right atrium and, in particular, in its lower part. In this situation, the value of venous blood saturation will be close to that for mixed venous blood.
It is obvious that today ScvO 2 monitoring surpasses SvO 2 measurement in popularity. In addition, despite the possibility of periodic measurement of SvO 2 /ScvO 2 by laboratory analysis of blood gas composition, continuous monitoring of the indicator by photometry is of particular interest. The theoretical justification for the advisability of continuous measurement of ScvO 2 may be the fact that in an unstable patient’s condition, the VO 2 /DO 2 balance depends on a number of conditions (Table 3) and is subject to rapid changes requiring immediate correction. Noteworthy is the fact that the effectiveness of ScvO 2 monitoring was proven in the well-known study by Rivers E.P. et al. namely using the method of continuous venous oximetry.
According to the literature, up to 50% of patients with shock have persistent tissue hypoxia (increased lactate levels and decreased ScvO 2) even against the background of normalization of vital signs and central venous pressure. Moreover, due to stable values ​​of vital parameters (heart rate, blood pressure, diuresis rate, etc.), patients arriving at the emergency room are often not fully examined for tissue blood flow disorders and do not receive adequate therapy during the “golden hours” – the period when organ dysfunction is reversible. This confirms the need for adequate treatment of intensive care patients from the first minutes of their admission to the hospital. The choice of an initially erroneous tactic of early therapy, within the narrow limits of the “golden” 6 hours after admission to the hospital, has an extremely adverse effect on the outcome, even with subsequent correction of treatment measures. Thus, in a study of patients with severe sepsis, it was shown that the early (within the first 6 hours after admission) use of a goal-directed therapy (EGDT) protocol, aimed, among other things, at achieving the target ScvO 2 value, led to the following results:
1) reduction in mortality by 15% (from 46.5% to 30.5%; p= 0,009);
2) reduction in the length of stay in the ICU by 3.8 days;
3) reduction in therapy costs by $12,000.
Proposed by Rivers E.P. etal. EGDT protocol (EarlyGoal- DirectedTherapy– early targeted therapy)(Figure 9.4) establishes target criteria that allow early identification of high-risk patients, and determines the tactics of early infusion and/or transfusion and/or inotropic therapy
based on the following targets:
– CVP = 8–12 mm Hg. Art.;
– ADVERSE > 65 mm Hg. Art.;
– diuresis rate > 0.5 ml/kg/hour;
– ScvO2 > 70% (continuous oximetry).

Picture 1. The protocol aims to
guided therapy Rivers E.P.
et al.(2001)
CVP – central venous pressure
laziness; ADSRED – middle arterial
no pressure; ScvO 2 – saturation
central venous blood
carbon; Mechanical ventilation
ventilation

Recommendations Surviving Sepsis Campaign 2008 include normalization of ScvO 2 (> 70%), which implies monitoring this indicator at the initial stage of treatment in patients with severe sepsis and septic shock.
However, in some situations, including septic shock, an increase in ScvO 2 may be observed, which is due to the “evasion” of blood flow from tissues as a result of shunting, a decrease in O 2 extraction and hyperdynamia, as well as other factors and their combination. In this context, the data is of interest
Bauer P. et al. (2008), who demonstrate that as a decrease (< 65%), так и повышение показателя ScvO 2 (>75%) during planned cardiothoracic interventions are accompanied by a significant increase in the incidence of complications and mortality in parallel with an increase in lactate concentration > 4 mmol/l. These results allowed the authors to conclude that for the ScvO 2 indicator the “safety corridor” lies
in the range between 65% and 75% (70 ± 5%).
However, a decrease in ScvO2 also does not necessarily indicate critical tissue hypoxia. Metabolic stress, observed during physical activity or a compensatory increase in O 2 ER against the background of chronic heart failure, will be accompanied by a compensatory decrease in SvO 2 / ScvO 2, which, however, is a relatively benign sign and is not accompanied by the development of MODS. It should be emphasized that the sensitivity of the ScvO 2 indicator is most likely not high enough to assess O 2 consumption by individual organs with isolated damage. According to Weinrich M. et al. (2008), during extensive abdominal interventions, the ScvO 2 indicator does not correlate with the oxygen saturation of venous blood flowing directly from the organ/area of ​​intervention.
However, several randomized trials suggest that the use of goal-directed therapy protocols based on ScvO2 targets in major surgery may be associated with a reduction in postoperative complications and mortality. According to our data, combined monitoring of ScvO 2 and intrathoracic blood volume (IHT) during coronary artery bypass grafting on a beating heart leads to an increase in intraoperative fluid balance, a decrease in the frequency of use of vasopressors and a decrease in the length of patient stay in the hospital. Car-
Diosurgery patients may experience multidirectional changes in ScvO 2 and SvO 2: Sander M. et al. (2007) argue that simultaneous monitoring of both indicators can increase the detection rate of global and local hypoperfusion. Monitoring venous saturation may also be useful in
patients with trauma, acute myocardial infarction and cardiogenic shock, facilitating early diagnosis of critical oxygen transport imbalances in these conditions. In addition, along with such indicators as hemoglobin concentration, hematocrit and base excess (BE), the ScvO 2 indicator in the case of adequate arterial oxygenation and normalization of CO can be considered as a convenient marker indicating the need for blood transfusion.

ScvO differences2 and SvO2
It should be recognized that applied clinical studies of central venous blood saturation began before the introduction of the Swan-Ganz catheter into widespread clinical practice, and, consequently, the possibility of measuring SvO 2. The question of the differences between the absolute values ​​of ScvO 2 and SvO 2 is mainly
academic interest. Unlike mixed venous blood, central venous blood gas composition reflects O 2 extraction by the brain and upper extremities/shoulder girdle. In clinical settings, ScvO 2 is regarded as a “functional analogue” (or “surrogate”) of mixed venous blood saturation. Central venous blood saturation less accurately reflects the global average O 2 ER, but is an accessible and convenient alternative to SvO 2 .
In a healthy person at rest, ScvO 2 is usually 2-4% lower than SvO 2, which is associated with higher extraction of O 2 in the organs of the upper half of the body, including the brain, which, with a weight of only 2% from body weight, can receive up to 20–22% of cardiac output. Despite
These differences, global changes in O 2 ER are accompanied by unidirectional and similar in amplitude shifts in the ScvO 2 and SvO 2 values.
As shock develops, the picture changes diametrically: ScvO 2 Always exceeds SvO 2 , with differences reaching 5–18%. According to Reinhart K. et al., with septic shock ScvO 2 exceeds SvO 2 by 8%. Cardiogenic and hypovolemic shock lead to suppression of splanchnic perfusion, which is accompanied by an increase in O 2 ER with
inevitable decrease in SvO 2. Thus, differences between ScvO 2 and SvO 2 may vary depending on a number of factors (Table 4). Thus, during anesthesia, ScvO 2 exceeds SvO 2 by 6%. Similar changes are observed with sedation and intracranial hypertension.

Table 4. Differences in saturation of central and mixed venous blood

Conclusions from clinical and experimental studies regarding the use of ScvO 2 as an alternative to SvO 2 vary. A number of researchers indicate the correspondence of changes in SvO 2 and ScvO 2 in various critical conditions. Some authors believe that ScvO 2 values ​​do not show close
correlation with SvO 2 , while monitoring the indicator does not allow the global VO 2 /DO 2 balance to be assessed with acceptable accuracy. The discrepancy between the values ​​of ScvO 2 and SvO 2 is especially acute in septic shock, which is accompanied by phenomena of mitochondrial distress. The severity of shunting and
the severity of mitochondrial dysfunction in the superior and inferior vena cava basins may differ; in such a situation, ScvO 2 cannot serve as an adequate substitute for SvO 2.50 Recent studies have shown that at the time of admission to the ICU, a decrease in ScvO 2 is observed only in a small proportion of patients with severe sepsis.
catfish In this regard, some experts consider the inclusion of ScvO 2 in standardized recommendations for the management of this category of patients to be premature.
However, a sharp decrease in ScvO 2 is almost always associated with a decrease in SvO 2 . Thus, ScvO 2 remains an important clinical parameter and can be considered as a reliable indicator of the imbalance between oxygen delivery and oxygen consumption.

Figure 2. Parallel due to
changes in mixed saturation
and central venous blood:
1 – normoxia; 2 – blood loss; 3 –
infusion therapy (HAES); 4 –
hypoxia; 5 – normoxia; 6 – hyper-
roxia; 7 - blood loss.
From: Reinhart K., Bloos F. Central Venous
Oxygen Saturation (ScvO 2).
Yearbook of Intensive Care Medicine
2002: Ed.: Vincent J.-L.:241–250

TECHNICAL SUPPORT FOR MONITORING VENOUS SATURATION

ScvO 2 and SvO 2 can be measured discretely by analyzing the gas composition of venous blood samples taken from a central venous catheter or the distal lumen of a Swan-Ganz catheter, respectively. However, for a number of reasons outlined above, continuous measurement of ScvO 2 /SvO 2 may have a number of advantages, in particular against the backdrop of rapid and difficult to predict changes in tissue blood flow and other determinants of oxygen delivery. Currently, there are several systems for continuous measurement of ScvO 2 /SvO 2, operating on the principle of venous photometry (oximetry). The continuous measurement method is based on the use of a small-diameter catheter into which fiber-optic conductors are integrated, one of which emits light of a certain wavelength into the venous blood flow, and the second transmits the reflected signal to the optical sensor of the monitor (Figure 3).

Figure 3. The principle
rupture reflective venous
no oximetry

1. CeVOX and PiCCO monitoring systems2 (Pulsion Medical Systems, Germany). The sensor for venous oximetry is installed through one of the lumens of the central venous catheter. Continuous ScvO 2 measurements require CeVOX (PC3000) or PiCCO 2 central units equipped with an optical module (PC3100) and a disposable fiber optic sensor (PV2022-XX, 2F (0.67 mm), 30–38 cm). To initially calibrate the monitor in vivo it is necessary to insert the sensor into the superior vena cava. After confirming a high-quality signal, a sample of venous blood is taken to determine its oxygen saturation and hemoglobin concentration. Entering these values ​​into the monitor menu completes the calibration procedure. The convenience of the system is that repositioning, removing or replacing the oximetry sensor does not require repositioning or removing the central venous catheter. According to a recent study by Baulig W. et al.6 (2008), ScvO 2 measured using the CeVOX system has acceptable sensitivity and specificity for predicting significant changes in the indicator. The PiCCO 2 system allows continuous monitoring of DO 2 and VO 2 values.

2. PreSep systemTM(Edwards Lifesciences, Irvine, USA) includes a triple-lumen central venous catheter with a pre-integrated fiberoptic guidewire for continuous ScvO 2 monitoring. The catheter can be connected to a number of Edwards Lifesciences systems, in particular Vigilance-I, Vigilance-II and VigileoTM. At 20 cm in length, the catheter diameter is 8.5F (2.8 mm). Calibration required before installation in vitro And in vivo. The quality of the ScvO 2 signal can be impaired by pulsation in the area of ​​the catheter tip, periodic contact with the vessel wall (catheter jamming), kinking and formation of a blood clot, and hemodilution. Updating the hemoglobin and hematocrit values ​​in the monitor menu is necessary when these values ​​change by 6% or more. Models with the “H” marker have traditional antibacterial and heparin protection
AMC Thromboshield cover. Currently, PreSepTM catheters are protected from bacterial contamination by a patented OligonTM complex (a complex coating including silver, platinum and carbon atoms), the action of which is based on the release of active silver ions.

3. CCOmbo system (Edwards Lifesciences, Irvine, USA) is a Swan-Ganz catheter with an integrated fiberoptic element. When connected to monitoring systems, Vigilance provides the ability to continuously measure SvO 2, CO, as well as end-diastolic volume and right ventricular ejection fraction. The cost of the catheter is relatively high.

INDICATIONS FOR MONITORING VENOUS SATURATION

According to a number of clinical studies, monitoring of central and/or mixed venous saturation may be indicated in the following situations:
– severe sepsis and septic shock;
– perioperative period of cardiothoracic interventions;
– myocardial infarction, cardiogenic shock and circulatory arrest;
– severe injury and blood loss.
Targeted therapy algorithms based on a specific SvO 2 /ScvO 2 value are in most cases aimed at increasing the determinants of oxygen delivery:
– increasing cardiac output (infusion therapy and inotropic support);
– normalization of hemoglobin concentration (hemotransfusion);
– normalization of external respiration (SaO 2) – methods of respiratory therapy.

At the same time, taking into account the nature of compensatory changes observed with inadequate distribution of tissue blood flow, methods that promote the redistribution of capillary blood flow (microcirculatory recruitment) and increase the extraction of O 2 by tissues (“metabolic therapy”) may be appropriate.
In conclusion, it is necessary to reiterate that maintaining adequate tissue perfusion and oxygenation is the main goal of therapy in intensive care patients. The feasibility of monitoring central venous blood saturation is that this method does not require additional invasive procedures.
interventions and has clear advantages in the early diagnosis of shock. In distributive shock, ScvO 2 does not always accurately reflect global oxygen extraction, however, changes in ScvO 2 as a result of treatment interventions significantly correlate with the dynamics of SvO 2. In such a situation, it seems rational to talk about a “corridor of safe values” for an indicator, and not just about its lower limit. Monitoring ScvO 2 may be useful during major surgical procedures, cardiogenic shock of various origins, blood loss and circulatory arrest.
Indicators of central and mixed venous saturation should be interpreted taking into account other hemodynamic indicators (heart rate, blood pressure, central venous pressure, CO, GKDO) and markers of metabolic activity of organs (diuresis rate, PvCO 2, gradient of tissue or gastric PCO 2 and PaCO 2, lactate concentration, etc. .). Measurement of venous saturation can be a useful “screening test” for further detailed assessment of hemodynamics, in particular the study of preload, cardiac output and other indicators. In critical conditions, the use of these indicators and early targeted therapy for disorders can help identify metabolic stress and tissue hypoxia and, consequently, select adequate treatment tactics. In addition, the venous saturation indicator, like other “metabolic markers,” can be used to assess the effectiveness and safety of a number of therapeutic measures, for example, weaning from mechanical ventilation or discontinuation of inotropic support.