Thermoregulation in newborns. Features of thermoregulation of newborns. Heat transfer in the body of a child, children

Many parents consider newborns to be smaller copies of adults, but this position is fundamentally wrong. The body of a newborn and a child in the first years of life differs from an adult in almost all respects. Therefore, they often experience diseases and conditions that almost never occur in adults. A special place in this issue is occupied by thermoregulation and the associated features of caring for the baby.

Thermoregulation system

For normal life, the human body temperature must remain constant, which is ensured by the thermoregulation system. During complex multi-stage physical and chemical processes, heat is generated and released. The balance between heat production and heat transfer is called temperature homeostasis, but in children this system is imperfect and requires external support.

How does a baby's thermoregulation system work?

The thermoregulation center is located in the hypothalamus, a special section located deep in the brain. It reacts to the temperature of the blood flowing to it and the concentration of special chemicals - hormones, pyrogens and mediators. In response to information from the periphery of the body, it sends impulses that regulate the processes of heat production and heat transfer. Thus, thermoregulation is carried out at the level of the autonomic nervous system - that is, autonomously (independent of our mind).

What is heat production

In humans, heat production occurs through voluntary muscle movements, involuntary contractions of muscle fibers (shivering when freezing), and through heat production by “nonmuscular thermogenesis.” In newborns, the main source of heat formation is the process of oxidation of brown fat reserves, which in newborns is approximately 7-8% (in adults there is none at all). It is located on the neck, near the shoulder blades, in the sternum area, near the kidneys. Reserves of brown fat gradually begin to form in a child from about 28 weeks of intrauterine existence. It is from this time that the baby will already try to generate heat and maintain body temperature if born ahead of time. The more of this fat in a child’s body, the better the baby is protected from hypothermia. The regulation of fat breakdown is regulated by the adrenal glands and the thyroid gland.

But the mechanisms of muscle tremors are less pronounced - newborns almost do not tremble when freezing, and the increase in oxidative processes with this mechanism is not so active. If children freeze, they begin to cry and actively wave their limbs, the mechanism of active heat production is activated.

What is heat transfer

To maintain the correct body temperature, it is necessary not only to produce heat, but also to release it into the environment to prevent overheating. Heat transfer is regulated by the nervous system by changing the tone of blood vessels - in order to release excess heat, skin vessels dilate and warm blood rushes to the surface. And when cooling, vascular spasm occurs, which allows heat to remain inside the body and heat loss decreases. But children do not have such a pronounced heat-insulating subcutaneous fat layer, so even if their skin vessels are spasmed, they can still lose heat from the surface of the body.

Heat transfer processes are carried out using four main mechanisms. The main one is convection - heat exchange between the baby’s body and air or water. That is why it is important for children to maintain a certain microclimate in the nursery or bathroom. It must be remembered that strong air currents can cause significant heat loss in newborns; it is important for them to avoid drafts in the house and strong winds when walking.

The second mechanism for heat release is its transfer from the surface of the body to other objects and surfaces. Avoid placing a naked child on metal scales without a warm diaper, try to prevent the child from coming into contact with cold surfaces - do not constantly touch the walls, metal parts of the crib or stroller with their handles.

Heat transfer is also carried out by radiation in the infrared range coming from deep within the body. If the environment is much cooler than the body, radiation is carried out quite actively into the external environment. When the ambient temperature rises to the child’s body temperature (for example, in the heat), it practically stops. But if there are cold walls or a window nearby, heat loss will be very strong, including in the center of the body. Swaddling and dressing the baby and warming him with the mother's body can help prevent such losses. In addition, in newborns, especially premature ones, heat loss is greatest in the head area - it requires wearing a hat or positioning in the crib with the head away from the wall.

The main type of heat loss in newborns is evaporation - they can lose moisture from their skin and lungs when they exhale. The baby is born wet, and its temperature decreases by 1-2 degrees due to the evaporation of amniotic fluid in the first minutes of life. This reflexively stimulates the first breath, but should not lead to hypothermia of the baby. In addition, due to active respiratory movements, quite a lot of heat evaporates from the surface of the lungs with liquid. But the process of sweating in children is not pronounced, so they overheat more easily than adults in the heat.

What is considered normal?

The temperature of children during the newborn period ranges from 36.4 to 37.5 ° C, but when screaming, crying, or anxiety, it can rise to 38 ° C or even higher. In the first days, due to fluid loss and labor stress, the temperature may rise to 38-38.5°C, but this quickly passes. To measure temperature, you must use a mercury or electric thermometer. This is done in the armpit, but today there are also ear thermometers that are fast and accurate.

Caring for the baby in the first days

Due to the evaporation of amniotic fluid, the newborn may suddenly become cold. Therefore, after birth, he is blotted with warm sterile diapers and placed on the mother’s chest, covered and wearing a cap. If the baby is full term, being naked at 25 degrees is equivalent to being a naked adult at zero temperature. The temperature of the mother's chest is 36-37°C, which warms the baby and allows thermoregulation processes to adjust and start. From the second or third day of life, the child’s thermoregulation gradually adjusts, although in the first months of life he still quickly overheats or becomes hypothermic.

How to create climatic comfort for your child

Now, knowing all the features of thermoregulation of newborn babies, it is necessary to properly organize their care. First of all, it is necessary to create the optimal temperature and humidity in the nursery - for newborns this is about 25°C and 60% humidity. During the first month of life, the temperature is reduced to 23-24°C, and in six months the optimal temperature in the house is 20°C, and for sleep 18-19°C.

This temperature regime will allow the child not to become hypothermic. At the same time, there will be no overheating if the baby is dressed correctly. At home, at 25°C, swaddling clothes or a long-sleeved cotton suit and socks are sufficient.

One of the important points in the formation of thermoregulation and the overall development of the baby is skin contact with the parents - during feeding, the mother is recommended to be naked and cuddle the naked baby, covering his body with a blanket on top. This is useful not only for the child’s thermal comfort, but also for the formation and maintenance of lactation, and the establishment of emotional connections. During colic, it is also useful to carry out similar activities - but then dad can also participate in them, pressing the baby to his warm belly. Contact with the parent's body balances the processes of heat production and heat transfer - the child feels comfort and falls asleep.

When bathing your baby, you need to choose the right temperature of water and air in the bathroom. Initially, the baby is bathed in water close to body temperature, and the temperature in the bath should be approximately 25-27 degrees, since heat loss occurs from direct contact with water and then wet skin evaporates more. As the baby grows, you can reduce the air and water temperatures - this will harden the baby and allow him to better adapt to changing weather.

Cold or overheated?

If the baby is cold, he turns pale, blueness appears in the area of ​​the nasolabial triangle, he is restless or inhibited. However, cool legs or arms are not a sign of freezing - they are always lower than body temperature due to more active sweating and the characteristics of blood circulation and nervous regulation. If the baby is cold, it is necessary to create skin contact - your body will warm him faster and better than any diapers; after all, its heat production is still slowed down, and from you it will receive living warmth. Only cases of hypothermia are rare - parents (and grandmothers are especially guilty of this) try to wrap the baby warmly and heat the room more, leading to overheating.

If, when freezing, a child begins to cry and move actively, if he overheats, he rarely lets you know about it in time - usually overheating is noticed by parents already in a severely painful condition. This is an increase in temperature to 38-39°C, a sharp attack of anxiety or excessive apathy, red and sharply moist skin, and refusal to breastfeed. The danger of overheating is a decrease in immunity and the ability to cool down faster due to sweating (remember the process of evaporation).

But how can you determine whether your baby is dressed correctly? it's simple - touch the back of your neck, it should be dry and warm. If it is wet and hot, you have overdone the diapers or clothes, and if it is dry and cool, then the baby is cool.

On walks

Walking is beneficial for any child, starting from the first days of life. But in order not to harm the baby, it is necessary to dress him correctly and walk in comfortable conditions. We start going for walks from the moment we return from the maternity hospital in the summer and on the 10th day in the winter. The air temperature for walking is selected from - 10 to + 30 degrees.

For your first walks, choose windless and non-rainy days; as you adapt, from the second or third month you can walk in almost any weather (except for hail, ice and storms). Gradually, walks should take at least 2 hours a day - an hour in the morning and in the evening.

If the baby is in a stroller, make sure that the sun does not overheat the air inside it; it is better to choose shade or fold back the canopy, allowing the baby to enjoy the sun. If the baby is walking in a stroller and does not move, you need to put on one more layer than you put on yourself. Take a blanket with you in the stroller; if there is wind, you can lightly cover (but not wrap) the baby.

On a walk, checking the comfort of his clothes is also easy - touch his neck. Many mothers feel the nose, which, like the legs and arms, is usually colder than the body and is not an indicator of freezing.

Maintaining body temperature for a child is one of the important tasks in life. It largely depends on the parents how correctly the thermoregulation system is formed and functions. It, like the entire body, can be trained through hardening; These procedures should be started from birth - then the child will be better able to tolerate fluctuations in temperature and humidity and will get sick less.

Thermoregulation is a complex process that reflects the manifestations of the subtle interaction of the human body with the external environment. Various parts of the nervous and humoral systems take part in its implementation.

Physiological mechanisms that determine the constancy of body temperature, i.e., carry out thermoregulation, are divided into chemical and physical. Chemical thermoregulation ensures an increase in heat production when the body is cooled (decrease in ambient temperature, increased heat consumption). The main source of heat production in humans is skeletal muscles (contraction of muscle fibers or increase in their tone). The second important source of heat production is the liver, along with the rest of the digestive organs. Physical thermoregulation carries out the processes of heat transfer from the body through convection, radiation and evaporation, with the main role played by the blood vessels of the skin. The division of thermoregulation into chemical and physical is to a certain extent arbitrary, since they are closely related to each other and mutually determined.

It is believed that heat production and retention of heat in the body are regulated mainly by the posterior nuclei of the hypothalamus, and heat loss and a decrease in heat production are carried out through the regulatory influence of predominantly the anterior nuclei of the hypothalamus. Removal of the hypothalamus leads to loss of the ability to regulate body temperature, making the animal poikilothermic.

The endocrine glands also play an important role in thermoregulation, especially the thyroid gland, adrenal glands and pituitary gland, the hormonal activity of which is regulated by the nervous system. The role of these glands is reduced mainly to the influence on heat production. Their impact on heat transfer is much less.

Thermoregulation in newborns has a number of features associated with the morphological and functional immaturity of central and peripheral mechanisms. In premature infants, the immaturity of the cerebral cortex is more pronounced than in full-term newborns. One of the reasons for the imperfection of thermoregulation in prematurely born children, apparently, is the deep functional immaturity of the interstitial brain. In the fetus, all the nuclei of the hypothalamus are formed at the time of birth and are similar in topography, structure and shape to the nuclei of an adult. However, the structural differentiation of hypothalamic formations is not yet complete and occurs much later.

Numerous studies by domestic and foreign authors have shown that the mechanism of chemical thermoregulation in newborns is quite well developed. Already in the first hours after birth, even in premature babies who have been cooled, heat production increases. Improvement of chemical thermoregulation in full-term newborns, according to O. V. Bepevskaya, occurs by the end of the 1st month, and in premature infants - at the 3-4th month of life. Inferiority of thermoregulation in the newborn period is associated with underdevelopment of the physical component of thermoregulation.

An interesting question is about the source of heat production in full-term and premature newborns. As is known, children of this age period do not have a tremor reaction when the ambient temperature drops, i.e., they are capable of generating heat production without engaging muscle activity. The processes of pesocortic inhibition are carried out by activating the sympathetic nervous system - the specific mediator is norepinephrine.

Recent studies have shown that brown adipose tissue is a powerful source of heat production. Brown adipose tissue, developing from mesenchymal cells, in children is located in the interscapular and axillary areas, in the thyroid and thymus glands, pericardium, around the esophagus, kidneys and adrenal glands, trachea, in the mesentery of the small intestines, in the groin and along the large vessels. It is believed that during cold exposure in newborns, oxidation of fatty acids in brown adipose tissue occurs, as a result of which a large amount of heat is released, tissue and blood are heated in nearby vessels.

Our observations of rectal and skin temperature in newborns exposed to cooling, carried out at the Institute of Pediatrics of the USSR Academy of Medical Sciences together with I. A. Kornienko, V. N. Bogachev, Yu. M. Pavlov and V. N. Tsukanov, showed that the average temperature ; the interscapular region is always higher; than the average skin temperature of the rest of the body. Our results are consistent with the opinion of Silverman, who also associates the rise in temperature in the interscapular region in children with an increase in heat production in brown adipose tissue. Examination of children using a thermal imager, which allows measuring the intensity of infrared radiation of tissues, confirmed the data obtained using conventional research methods. In healthy full-term and premature newborns, the response to cooling at a temperature of 21-23°, despite various individual characteristics, is always associated with activation of heat production in brown adipose tissue.

The formation of heat as a result of an increase in metabolic rate under the influence of cooling occurs, of course, not only in the cells of brown adipose tissue. These processes also occur in other tissues, but the role of heat formation in brown adipose tissue during the newborn period is very significant.

Before the birth of a child, “training” of thermoreceptors and, in general, the entire heat production system is reduced to a minimum due to the fairly high stability of the body temperature of a pregnant woman. The transition of a child to extrauterine existence is accompanied, first of all, by a powerful load on thermoreception, since the temperature of the air around him is 10-14° lower than the temperature at which the fetus develops.

In a newly born child, the temperature measured in the rectum ranges from 37.7 to 38.2°. According to A.V. Tokareva, in the first hours of life, the body temperature of a newborn corresponds to the mother’s body temperature. At the age of 3 hours of life, the temperature drops to 35.2°, and then rises again. In the first 5 days of life, body temperature undergoes significant fluctuations; from the 6th day it is established at a relatively constant level (36.2°), although complete stabilization occurs only at the beginning of the 2nd month of life.

In premature babies, according to Yu. A. Mucheidze, who carried out his observations at the clinic for premature babies at the Institute of Pediatrics of the USSR Academy of Medical Sciences, the level of rectal temperature, despite special warming measures, in the first 10 days of life is quite low (35.3 °). This means that the function of heat generation in a physiologically immature organism, such as a premature baby, is not able to provide the level of thermal energy at which normal life activities are carried out. There were sharp fluctuations in body temperature during the day, which were more pronounced the greater the degree of prematurity of the child. In children aged 1 month, the temperature becomes relatively stable (its average level is 37.2°).

The skin and its vascular system play a major role in maintaining body temperature. Full-term infants are characterized by a high level of skin temperature compared to an adult, which is explained by a high level of metabolism, the prevalence of vasodilatory reactions, and structural features of the blood supply to the skin. The skin temperature of the central areas of the body in full-term newborns is higher than in the peripheral areas. In the first days of life, the skin temperature on the left half of the body is higher than on the right, according to 11. Koeva-Slavkova, by 0.17°. A.V. Tokareva also noted the asymmetry of skin temperature in children throughout the entire neonatal period. According to her data, the highest level of skin temperature on the first day of life was noted in the hypochondrium (35.2°), on the skin of the chest (34.9°), on the hands (34.5°), and the lowest on the fingers stop (31.7°).

Premature babies, according to 10. A. Muchaidze, are characterized by higher skin temperatures than full-term babies and adults. The more premature the baby, the higher his skin temperature. Thus, the insufficiency of heat generation function in premature infants is aggravated by heat dissipation through skin radiation. In premature infants, the skin temperature of the proximal limbs did not always exceed the skin temperature of the distal limbs, sometimes it was equal to it or lower. The maximum difference in skin temperature in different parts of the body in premature infants during the first 10 days of life was 2.5°, at the age of 1 month - 1.4°.

A decrease in skin temperature in the absence of changes in rectal temperature begins only in the 3rd month of life, which can be considered an external manifestation of the beginning of vascular regulation of skin radiation in these children.

A study of the Shcherbak reflex in premature infants conducted by Yu. A. Muchaidze made it possible to obtain a more in-depth characteristic of the level of maturity of thermoregulation mechanisms. When a child's hand was immersed for 15 minutes in a bath of warm water, instead of the expected rise in body temperature that occurs in adults, the rectal temperature in premature infants during the first 10 days of life dropped by 0.4-1.2°. An increase in temperature to the initial level was not observed within 4-5 hours. In children weighing more than 1500 g at birth, fluctuations in skin temperature were similar to rectal temperature. In very low birth weight infants, skin temperature produced greater changes in the arm opposite the thermal stimulus. One might think that the described type of reactions in children during the first 10 days of life to a heat test indicates an inability to urgently stabilize the temperature of the internal environment of the body. Only from the end of the 2nd - beginning of the 3rd month of life does some normalization of response data occur during the Shcherbak test.

Inconsistency in the system of mechanisms ensuring heat production and heat transfer indicates that by 6-7 months of intrauterine development, the functional thermoregulation system has not yet formed as a unit of physiological integration.

The establishment of a daily periodicity of body temperature may indicate the time of improvement of the thermoregulation function on the part of higher central mechanisms. There is no clear information about this process in the literature. N.A. Arkhangelskaya believes that from the first days after birth, children experience a daily periodicity of body temperature that is the opposite in value to that of the mother. N. Koeva-Slavkova observed a daytime increase in temperature and a decrease at night, i.e., a daily periodicity in full-term newborns already on the 4-5th day of life.

V.N. Bogachev, who studied the function of thermoregulation in newborns and infants, noted the appearance of a daily rhythm of body temperature in full-term children at the age of 1 month. However, he believes that the periodicity of body temperature that has emerged is still significantly different from that observed in adults. The daily rhythm of heart rate and breathing in these children begins to correlate with body temperature from the beginning of the 2nd month of life.

Hellbrugge, who has extensively studied the formation of circadian rhythms in newborns, believes that the daily periodicity of body temperature is established in the 2-3rd week of life.

The temperature analyzer in premature infants develops more slowly and matures structurally and functionally at a later date. According to Yu. A. Muchaidze, in premature babies during the first 3 months of life there is no daily periodicity of body temperature, and only at the end of the 3rd - at the beginning of the 4th month in some children who weighed 2000 g at birth, a tendency to daily increase appears temperature and some decrease at night. This, according to the author, may indicate that the cortical section of the temperature analyzer is turned on.

Due to the morphological and functional immaturity of a premature baby, their heat generation reserves are extremely limited. Even with inflammatory diseases, in which an increase in temperature is specific, hyperthermia in premature infants, as a rule, does not occur.

Research by Yu. A. Muchaidze showed that nursing extremely premature babies in closed incubators (i.e., in conditions that protected their body from excessive energy losses) accelerated the maturation of the thermoregulation function.

Since in early ontogenesis the improvement of chemical thermoregulation precedes physical thermoregulation, due to this, overheating easily occurs in newborns. The reason for this lies not only in insufficient regulation of heat release by convection and radiation, but also in the characteristics of sweating. Sweat glands in newborns are still underdeveloped and their sweat secretion is limited. The onset of sweating was registered in some children on the 4th day; this reaction was most clearly detected in children at the end of the 3rd - beginning of the 4th week. There was no correlation between the child's weight and the onset of sweating. Children in the first 7-10 days of life do not tolerate cooling well. A.V. Tokareva showed that a newborn child left without clothes at a temperature of 26° and even 28° experiences a drop in skin temperature, restlessness, hiccups, acrocyanosis, and urination.

The imperfection of thermoregulation in newborns, which in general terms consists of reduced heat production and increased heat transfer, should be taken into account when organizing their temperature regime. This is directly related to full-term newborns, in whom in the first 7-10 days of life there is an improvement in chemical regulation, metabolism and relative stabilization of body temperature. Daily heat production, which, according to V.P. Spirina, in full-term newborns on the first day of life is 45 cal, increases in subsequent days and on the 7th day is 58 cal. The optimal temperature regime for full-term and premature newborns should be considered one in which the child maintains a constant body temperature with the least amount of thermoregulation stress.

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The body of a newborn, accustomed for 9 months to a temperature of 38°C in the mother’s womb, when faced with new conditions where the temperature is 10-15° lower, does not yet have adaptation mechanisms. This can lead to hypothermia of the body and the development of diseases against this background. On the other hand, cooling an infant is sometimes necessary for medical reasons.

Symptoms of hypothermia in a newborn

Parents of a newborn child should carefully monitor his condition, avoiding hypothermia, and at the same time train the baby’s body, develop the mechanism of thermoregulation in it. This should be done very gently and gradually, avoiding sudden changes in the temperature of the environment surrounding the newborn.

And yet, it often happens that the baby gets cold. Since he is not yet able to report this, parents need to be very careful and know how hypothermia in the infant manifests itself.

Signs of hypothermia in a newborn:

• Change in skin color: it acquires a bluish tint, may have a spotted “marbled” appearance, cyanosis is characteristic of the upper lip;
• The skin in natural folds (armpits, groin, elbow and popliteal fossae) is cool to the touch;
• Hiccups;
• Trembling in the body;
• Dry cough;
• Decrease in body temperature to 35-34°C.

Important: a cold nose, fingers and toes are not symptoms of hypothermia, but are associated with blood circulation characteristics.

Treatment of hypothermia in a newborn

What to do if an infant shows signs of hypothermia? Tactics depend on how long the newborn has been in conditions of low temperature, but his condition is more important.

If the newborn is active, mobile, reacts quickly to communication with him, if the temperature is not lower than 35.5 ° C, he just needs to be warmed and fed.

The best option for natural warming is to attach the baby to the mother’s body, wrap in a warm blanket, breastfeed or, if he is bottle-fed, with a warm (37-39°C) nutritional formula. If these measures are not enough, you need to give the child a warm bath.

It is important to observe the temperature regime: at first the water should be 32°C, then gradually increase the temperature to 37°C, adding hot water after removing the baby from the bath.

In the water, you need to give a light massage to the child’s body, such as stroking and weak kneading between two fingers, make gentle movements with the arms and legs, turn him over on his side, stomach, and back again.

If the baby relaxes and begins to actively move in the bath, the skin acquires a normal pink color - the warming effect has been achieved. The duration of the bath is 10-15 minutes.

After a bath, wipe the newborn dry with a soft towel, put on cotton and warm underwear, warm socks, a cap, and cover with a blanket. After half an hour, you need to measure the baby’s body temperature.

If the baby has trembling, bluish skin, lethargy, refusal to eat, cough, runny nose, or body temperature has dropped to 35°C or lower, you should immediately consult a doctor.

It is impossible to give such a newborn a bath, much less put him to bed. Sleeping during severe hypothermia is dangerous; it can mask developing complications.

Consequences and complications

Hypothermia in a newborn is very dangerous. It leads to impaired blood circulation and, as a consequence, hypoxia (oxygen starvation) of all organs and tissues. The brain is most affected. This is precisely what explains the excessive calmness of a child when he is cold.

Hypothermia of a newborn in the absence of timely measures to warm the baby’s body can lead to a number of inflammatory complications:

• Upper respiratory tract (rhinitis, laryngitis, tracheitis);
• Tonsils (tonsillitis);
• Paranasal sinuses (sinusitis);
• Bronchos (bronchitis);
• Lungs (pneumonia);
• Kidney (glomerulonephritis, pyelonephritis).

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More severe consequences include frostbite, cerebral coma and death..

Frostbite of the extremities in this case is not associated with exposure to the cold, but with prolonged circulatory impairment due to vascular spasm and tissue hypoxia. The same is the reason for pathological changes in the brain.

Prevention of hypothermia in newborns

Since ancient times, the most important warming factor for a baby is maternal warmth. It has been established that if a newborn up to 2-3 weeks does not have contact with the mother’s body for 20 minutes or more, his temperature begins to decrease. This should be remembered, especially for young mothers, despite modern views, raising children in a Spartan spirit and “not teaching them to use their hands” is a delusion.

Important: you should not wrap your newborn too much. Overheating leads to sweating, and wet underwear will certainly lead to hypothermia and a cold. A sweaty baby should be wiped dry with a towel and changed.

The newborn needs help to adapt to new, harsher living conditions.. This process inevitably occurs when changing linen, washing, and daily bathing of the baby. You need to keep the child naked for 2-3 minutes 2 times a day, gradually increasing the time to 10 minutes.

From 2 weeks of age they begin to walk in the fresh air. In this case, the child must be warmly dressed and protected from the wind. It is useful to gradually increase the duration of bathing, to create conditions for the baby to swim in the bath.

You should also not use extreme methods - steam room, cold water, rubbing with snow and the like. All questions regarding the hardening of a child must be agreed with the pediatrician.

Indications for the use of artificial hypothermia in infants

Hypothermia or hypothermia of the newborn's body can also serve a good purpose when it is carried out for medical reasons.

• With asphyxia of the newborn;
• For encephalopathy;
• With metabolic acidosis;
• With convulsive syndrome;
• If the Apgar score is less than 5 points.

All of the above conditions are accompanied by oxygen starvation, which ultimately leads to organ failure.

According to statistics, every year 1 million children are born in the world with hypoxia of various origins, and, as a result, 20% of them develop cerebral palsy (CP).

The role of artificial hypothermia in newborns is to reduce the overall metabolism and, accordingly, the need of body cells for oxygen. Under hypoxic conditions, cooling prevents the death of cells, in particular the brain, and preserves their viability.

Therapeutic hypothermia of newborns

A newborn who is indicated for artificial cooling is placed immediately in the intensive care unit, connected to an artificial lung ventilation device (ALV), and a catheter is installed in the veins for constant supportive drug therapy.

Sensors of basic functions are connected, including body temperature, all information from which is constantly visible on the monitor (pulse, pressure, cardiography, encephalography, body thermography).

After all the necessary studies and emergency drug therapy, the child is connected to an artificial hypothermia apparatus no later than 6 hours from the moment of birth. The newborn hypothermia device has 2 sensors: one is applied to the skin, the other is inserted into the rectum. Cooling of the body lasts for an hour to a temperature of 34–33°C.

The duration of the procedure is 3.5 days (84 hours), it is carried out in 2 stages:

Craniocerebral hypothermia of an infant

Neonatal head cooling is a very important life-saving procedure for infants born with encephalopathy. It develops as a result of asphyxia and oxygen starvation of the brain when entangled in the umbilical cord, difficult childbirth with compression of the head and other reasons.

As a result of oxygen starvation, a newborn develops cerebral edema, metabolic processes in the nervous tissue are disrupted and damage occurs. These changes are usually irreversible. The most common outcome is various kinds of paralysis and other disorders of the central nervous system.

Craniocerebral hypothermia of newborns during asphyxia allows to reduce the activity of vital processes in the brain, thereby reducing its need for oxygen by 6–7% for each reduced degree of temperature. As a result, hypoxia is eliminated.

Cooling is carried out from above - from the bones of the skull, membranes and cortex of the brain to its deeper structures. At the same time, the flow of blood into the brain, passing through the arteries from below, remains normal. Most of the brain's neurons, even in severe encephalopathy, are preserved.

The human body is able to respond to any changes in the temperature regime of the environment, and our thermoregulation system is responsible for this, which, when the body cools, turns on the heating mechanism, and when the body temperature rises, it uses various methods of cooling it. There are suchtypes of thermoregulation, both chemical and physical. In this case, the constancy of body temperature in various environmental conditions is achieved through a balance between heat production and heat transfer. How does this happen?

At low external temperatures, the processes of chemical regulation of energy metabolism begin in the human body. Activation of metabolism with accelerated breakdown of carbohydrates and fats leads to the formation of additional portions of energy. At the same time, a number of physiological processes occur in the body, leading to a slowdown in heat dissipation. Methods of physical thermoregulation include constriction/dilation of skin blood vessels, sweating, the reaction of smooth muscle fibers of the skin, and even changing the posture in which a person is located. When we get cold, there is a sharp decrease in blood flow to the skin, causing the surface of the body to become cold, and the temperature difference between the skin and the environment is neutralized. In addition, contraction of the skin muscles leads to a change in the position of hairs on the skin, increasing its heat-protective properties. Also, when the temperature drops significantly, the muscle tremors mechanism is activated, helping a person to warm up better.

If the human body is exposed to high temperature, then chemical reactions inside the body lead to a slowdown in metabolism and a decrease in energy production. Physical regulation is adjusted to a cooling mode, which is achieved through blood flow to the vessels of the skin, which helps reduce its temperature. A person also experiences increased sweating, which not only helps remove heat through sweat, but also helps cool the skin with any air movement.

Thermoregulation in childrenmuch less developed than in adults. The large surface area of ​​the skin per kilogram of weight, as well as the dense network of skin vessels in infants, contributes to more active heat transfer. In addition, children sweat very little, and muscle tremors do not occur at all at low temperatures. Thermoregulation is carried out only through chemical mechanisms - accelerating or slowing down the production of internal heat. This imperfection of the heat exchange system leads to the fact that small children can easily freeze in a relatively warm room and quickly overheat at the slightest increase in temperature. Experience shows that most often children overheat. They get cold less often.

Violation of thermoregulation in a child

There are various pathologies of thermoregulation that are characteristic of both children and adults. However, in children they manifest themselves to a greater extent, due to the fact that they lead to more tangible consequences. One of the most common heat exchange disorders is the imperfection of the physical mechanism of heat regulation. In this case, when the temperature drops, the blood vessels in the skin narrow, and at the same time their tone decreases, which leads to bouts of sneezing and difficulty breathing. To avoid this, the body is forced to turn on the mechanism of chemical thermoregulation at sufficiently high temperatures, as a result of which a person begins to freeze and shiver even in warm weather.

The other extreme is when the chemical regulation mechanism turns on too late, and the person does not feel cold and trembling, but his body becomes severely hypothermic. This can lead to constant colds and exacerbations of chronic inflammatory processes in the ENT organs.

Some children develop a so-called cold allergy. Of course, cold air cannot be an allergen, but under the influence of low temperature, the baby’s own proteins can form a special structure that the child’s immune system perceives as foreign. As a result, some children develop skin rashes on their bodies. In order to avoid this, doctors recommend that parents do not dry out the child’s skin with soap, moisturize it with a special one after each bath, and also use a rich cream before going out for a walk in the cold. Apply the cream to the baby's face, neck and hands.

Thermoregulation disorders develop in almost all premature babies. Also at risk are children suffering from neurological and muscular diseases, diseases of the circulatory and respiratory systems. Therefore, if your child is weak, be sure to pay attention to, and use different ones at home.

Be sure to take everything into accountFeatures of thermoregulation in children, and try to avoid the most common mistakes in caring for a baby:

• Only in the first months of a child’s life the temperature in the room can be 24-25°C. Then it should decrease. And the optimal temperature for a children's room is considered to be 20-22 °C during wakefulness and about 18 °C during sleep.
• There is no need to put any hats or extra blouses on your child at home. It is ideal if you teach your child to sleep naked. If the room is cool, one diaper is enough.
• Pay attention to the first signs of overheating - breast refusal, restlessness, redness and increased body temperature of the baby. If you do not notice them, after some time the child will fall into a state of painful sleep and, with prolonged overheating, his temperature will rise to critical.
• Hypothermia in this sense is less dangerous, since the child will inform you about it by loud crying and active body movements. The fastest way to warm him up is to go into a warm room, put the baby to your chest, or give the baby warm tea.
• Learn to correctly determine your baby's body temperature. Often parents begin to feel the arms, forehead or nose. It is best to place your hand on the back of the baby’s head. If it is wet and hot, the baby is overheated. If the back of the head is cool, dress your baby warmer or cover him with a blanket.

FEATURES OF THERMOREGULATION IN CHILDREN. It is known that in a growing organism metabolic processes constantly occur with high intensity and various forms of metabolic energy received and expended are converted into heat. A significant contribution to the formation of heat in a child's body (heat production - TP) is made by the high levels of metabolism and physical activity characteristic of children. The accumulation of heat in the body contributes to an increase in body temperature. However, in accordance with the physical laws of heat transfer, if the temperature of any body, including the human body, becomes higher than the temperature of the environment of its existence, heat from the surface of the body begins to dissipate into this environment (heat transfer - TO), which helps to lower the body temperature. It is obvious that the temperature for a given body will be constant provided that the values ​​of TP and TO are equal. It is the maintenance of equality of heat production and heat transfer in conditions of changes in the intensity of metabolism, physical activity of the body and (or) the temperature of the living environment that is one of the most important functions of the thermoregulation system.

The value of body temperature, upon achieving equality between the values ​​of TP and TO, could be set at various arbitrary levels, but thanks to the function of the central - hypothalamic - thermoregulation centers, this temperature value is quite definite (“37 ° C). This is called the thermoregulation set point. Thus, the formation by the central neural structures of the hypothalamus of a certain temperature regulated in a given organism is the second most important function of the thermoregulation system. If both of these functions are performed successfully, then the thermoregulation system provides a solution to its main task - maintaining the temperature of the brain and other tissues of the “core” of the body at a relatively constant level. This temperature is maintained at a minimum voltage of the thermoregulatory mechanisms in conditions of slight fluctuations in the temperature of the external air environment or within the so-called thermoneutral, or thermally indifferent, zone - for a naked adult in the range of 28-30 ° C, for a newborn - 32-34 ° C, and for lightly dressed children aged 1 month - 22-25 °C, 6 months - 19-23 °C, 1 year - 17-21 °C.

Heat production. The total heat production in the body consists of primary heat released during metabolic reactions that constantly occur in all organs and tissues, and secondary heat generated when the energy of high-energy compounds is spent to perform muscle work and other functions. TP in the child’s body depends on the value of the basal metabolic rate, the “specific dynamic action” of food intake, muscle activity and changes in metabolic rate associated with changes

ambient temperature (facultative thermogenesis). Metabolic processes are carried out with unequal intensity in different organs and tissues, and therefore the contribution to the overall TP of the body of individual organs and tissues is unequal. The greatest amount of heat is generated in the organs and tissues of the “core” of the body: liver, kidneys, brain, working muscles (with tonic tension and contraction - contractile thermogenesis).

The amount of heat necessary to maintain body temperature is produced in a full-term baby immediately after birth. TC in a newborn is about 1.5 kcal per 1 kg of body weight per 1 hour. An increase in heat production after birth is ensured by the activation of the oxidation of free fatty acids in the mitochondria of fat cells, the level of which increases with an increase in the tone of the sympathetic nervous system, stimulation of beta-adrenergic receptors by catecholamines and activation protein kinase A, which increases the activity of the enzyme brown adipose tissue lipase (BAT). A more powerful and long-lasting increase in heat production is achieved by the action of thyroid hormones on mitochondrial oxidation processes in fat cells. In this case, the enhancement of TP is achieved by accelerating basic metabolic processes (basal metabolism) and activating the mechanisms of facultative thermogenesis, which ensure increased heat generation under conditions of lowering the ambient temperature. Both the intensity of basal metabolism in the body and the thermogenic function of brown adipose tissue depend on the level of thyroid hormones. Oxidation of fatty acids in brown adipose tissue, the mass of which in a full-term newborn is about 2% of body weight (25-35 g), occurs without significant synthesis of macroergs and with the maximum possible formation of primary heat. White adipose tissue of a newborn is also capable of direct heat generation, but to a much lesser extent. Through the mechanism of non-contractile thermogenesis, the level of heat production can be increased several times compared to the level of basal metabolism. At the same time, even in full-term babies, the reserves of heat-forming adipose tissue, including brown, quickly decrease, reaching a minimum by the 3-4th week after birth. The higher the serum level of T4 and T3, the higher the level of gene expression in the nuclei of adipocytes of brown adipose tissue, which are responsible for the synthesis of the thermogenin protein, which uncouples the processes of respiration and phosphorylation, reduces ATP synthesis in mitochondria and increases heat generation. T3 influences thermogenesis in brown adipose tissue by modulating the activity of the enzyme deiodinase D2, which determines the rate of formation of other active forms of thyroid hormones from T4 and their metabolic breakdown in tissues. Maximum stimulation of thermogenin gene expression is achieved by the simultaneous action of thyroid hormones and catecholamines. By the time of birth, this action reaches its greatest severity and provides the conditions for maximum thermogenic activity of brown adipose tissue in the early postnatal period.

With a significant degree of prematurity, when newborns have varying degrees of hypothyroidism, and the mass of brown adipose tissue is less than 1% of body weight, heat production is reduced. This can contribute to the development of hypothermia if conditions are not created to limit heat loss.

Contractile thermogenesis is also an important mechanism for increasing TP in a newborn, who already from the first hours of life has an increase in muscle tone and motor activity, which sharply increases with the effect of Holdov on the skin. The role of contractile thermogenesis in increasing heat production increases as the child’s age increases and the mass of brown adipose tissue decreases. This is facilitated by an increase in muscle mass in children, the development of mechanisms of thermoregulatory muscle tone and cold shivering. The contribution of contractile thermogenesis to TP can change in a number of neurological and muscular diseases, as well as in the development of hypoxia caused by diseases of the circulatory and respiratory organs.

Heat production per 1 kg of body weight increases during the 1st year of life to 2.4 kcal per 1 hour. In children over 2 years of age, heat production per unit of body weight at rest gradually decreases, but at the same time their relative body surface area decreases, and by 15-17 years, heat exchange rates and the development of thermoregulation mechanisms approach those characteristic of adults, when TP and TO become balanced and amount to about 1 kcal per 1 hour.

The level of heat production is controlled by effector neurons of the posterior hypothalamus through somatic and sympathetic nerve fibers, as well as a number of hormones and biologically active substances (norepinephrine, adrenaline, thyroxine, triiodothyronine, etc.).

Heat dissipation. The following mechanisms of heat transfer by the body to the environment are distinguished: radiation, heat conduction, convection, moisture evaporation. TO in the first three ways can be carried out only under the condition when the temperature of the body surface is higher than the temperature of the environment of existence. Maintenance due to the evaporation of moisture can be carried out both in the presence of a positive temperature difference between the surface of the body and the environment, and in conditions of a higher ambient temperature. Maintenance by evaporation stops at 100% saturation of the external

air environment with water vapor or in water. All of the above methods of heat transfer are subject to physical laws.

Due to the occurrence of physiological reactions of the body to the effects of heat, cold or a significant change in heat production, it is possible to influence the value of the body surface temperature, and thereby the value of the temperature gradient between the body surface and the environment and the value of TO. These reactions are vascular reactions - narrowing or dilating of the superficial vessels of the skin. If vasodilation is not enough to increase heat transfer (in conditions of high external temperature), then sweating is stimulated, which creates additional opportunities to enhance heat by evaporating more moisture from the surface of the skin and lowering body temperature. In conditions where, under the influence of cold, vasoconstriction is insufficient to reduce heat loss and prevent cooling of the body, physiological reactions of increasing TP are stimulated (contractile and non-contractile thermogenesis). Thus, HT by any method is by its nature a passive physical process, and physiological thermo-regulatory reactions of blood vessels or sweating only contribute to changing the conditions for dissipating more or less heat into the environment and achieving a balance between the values ​​of TP and HT.

Radiation is a way of transferring heat from the surface of a body to the environment in the form of electromagnetic waves in the infrared range. The amount of heat dissipated by radiation into the environment is proportional to the surface area of ​​the skin of those parts of the body that come into contact with the air. At an air temperature of 30-34 "C and a relative air humidity of 40-60%, the surface of the body of a naked child of the 1st month of life dissipates by radiation about 40% of the total heat given off. This radiation increases with a decrease in ambient temperature and (or) an increase in skin temperature and decreases with an increase in the temperature of the external environment and (or) a decrease in the temperature of the skin. If the ambient temperature exceeds the average temperature of the skin, the human body, absorbing infrared rays emitted by objects, warms up. If the temperature of the surface of the skin and the environment is equalized, the transfer of heat stops.

The skin of newborns and young children is well vascularized, and due to the intense flow of heated blood to the surface of the body from the internal organs, the skin temperature in children is higher than in adults. In addition to the higher temperature gradient between the body surface and the external environment, children have a number of other factors that cause intense heat. This is 2 times the body surface area per 1 kg of body weight, small thickness of the skin and its low thermal insulation properties, especially if the subcutaneous fat layer is insufficient.

The maturation of heat regulation mechanisms in a child lags behind the development of heat production regulation mechanisms and is actually completed only by the age of 7-8 years. Earlier (by 6 months-1 year), the mechanisms of regulation of TH through the reactions of superficial vessels mature, the nature of which can be judged at room temperature by the change in temperature difference on the chest and limbs of a naked child.

An increase in the functional activity of the sweat glands and the regulation of sweating develop in children at a later date. The delay in the development of mechanisms that control heat transfer, in comparison with the development of mechanisms for regulating heat production, means that if basic precautions are not observed or with the development of certain diseases, overheating of children in the first months and years of life is more likely than their hypothermia.

Conditions of overheating or hypothermia of a child's body are especially likely when the body comes into contact with an aqueous environment (baths) or with other physical bodies (cold operating table and other conditions), when heat is dissipated through heat conduction. The intensity of heat treatment also depends on the temperature gradient of the contacting bodies, the area of ​​the contacting surfaces, the time of thermal contact and the thermal conductivity of the contacting body. Dry air and adipose tissue are heat insulators, while wet clothing, humid air and water saturated with water vapor, on the contrary, are characterized by high thermal conductivity.

High rates of heat dissipation and overheating or hypothermia of the child's body are achieved when they transfer heat to convection currents of air or water. Naked children of the 1st month of life at an air temperature of 30-34 ° C give about 36% of their heat to convection air currents.

The high intensity of heat in children is also facilitated by the dissipation of heat through the evaporation of moisture from the surface of the body and from the mucous membrane of the respiratory tract. In children, a significant amount of moisture sweats through a thin layer of the epidermis of the skin and constantly evaporates from the surface of the skin (imperceptible perspiration). The total amount of heat dissipated by the naked body of a child due to the evaporation of water is, under normal conditions, about 24%. When the external temperature exceeds the average skin temperature, the body cannot release heat to the external environment by radiation, convection and conduction. Under these conditions, the body begins to absorb heat from the outside, and the only way to prevent

its overheating becomes an increase in heat dissipation through sweating and evaporation of moisture from the surface of the body. Sweating begins in newborns when the rectal temperature rises to 37.2 ° C (sweating threshold) and reaches its greatest intensity after 35-40 minutes. In newborns, the density of sweat glands is higher than in adults, but their functionality is lower. A child's sweat glands can produce up to 57 ml of sweat per 1 kg of body weight per day, and an adult - up to 500 ml. With age, the temperature threshold for sweating decreases and the functional activity of the sweat glands increases.

Evaporation of moisture is possible as long as the ambient air humidity remains less than 100%. With intense sweating, high humidity and low air speed, when droplets of sweat, without having time to evaporate, merge and flow from the surface of the body, heat transfer by evaporation becomes less effective and overheating of the body may occur.

Blood circulation plays a decisive role in removing heat from internal organs and tissues that produce it in large quantities and preventing their overheating. Blood has a high heat capacity, and by increasing or weakening the blood flow directed to the surface tissues, heat is transferred to the surface of the body, warming or cooling it, and creating conditions for greater or lesser heat transfer to the environment.

The level of regulated body temperature is established in the body by the hypothalamic thermoregulation centers. It is most likely that the preoptic area, whose neurons are sensitive to small changes in local temperature and control all types of thermoregulatory reactions that occur when the temperature deviates from the set point for regulation, is directly related to determining the value of the regulated temperature (set point). If the local temperature of the preoptic area deviates above the level set for regulation, for example, when the child’s physical activity increases, then thermoregulatory reactions will be initiated in the body, increasing heat transfer, contributing to a decrease in body temperature and returning the local temperature of the preoptic area to the value set for regulation (about 37 °C). If the local temperature of the preoptic area drops below a set value, for example, when cooling during swimming, then thermoregulatory reactions will be initiated, reducing heat loss, and, if necessary, increasing heat production and helping to increase body temperature and return the temperature of the preoptic area to a given level. The preoptic area of ​​the hypothalamus contains (about 30% of the total number) heat-sensitive neurons (TSN), which receive afferent signals through synaptic inputs from thermal receptors (TR) of the skin and other tissues, and heat-insensitive neurons (TIN) (about 60%), which receive afferent signals from Cold receptors (CRs).

In both full-term and premature babies, skin receptors are well developed. The most sensitive area of ​​thermoreception is the skin of the face, innervated by the trigeminal nerve. About 10% of neurons are classified as cold-sensitive (CSN), since their activity increases with decreasing temperature. Since the neurons of the preoptic area are sensitive to both changes in local temperature and signals coming from thermoreceptors about the nature of temperature changes in the periphery, they integrate both of these types of information and, depending on the obtained value of the integral body temperature, send one or another signal to effector neurons, triggering thermoregulatory reactions.

Thus, heat-sensitive neurons, under conditions of thermally indifferent ambient temperature and a slight (>0.011 °C) increase in the local temperature of the preoptic area above 37 °C, activate effector neurons through excitatory synapses, located in the posterior hypothalamus and triggering thermoregulatory reactions of heat transfer. At the same time, heat-sensitive neurons can, through inhibitory synapses, inhibit the activity of effector neurons that control the level of heat production in the body. But under conditions of high ambient temperature, when the TNs receive an activating afferent influx from thermal receptors, the heat transfer reaction can be triggered by them through the activation of effector neurons, when there has not yet been an increase in the local temperature in the preoptic area.

When exposed to cold, the afferent influx from the ChR enters heat-insensitive neurons, which, after their activation, can have an excitatory effect on effector neurons that trigger reactions to increase heat production, and at the same time can inhibit the activity of effector neurons that control the level of heat transfer, while reducing heat dissipation.

On effector neurons, the activity of which depends on the receipt of signals to them from both the TCN and the TNN of the preoptic area, there are both excitatory and inhibitory synaptic inputs. It is obvious that effector neurons will be activated if the input of signals through excitatory synapses predominates, and reduce their activity if the input of signals through inhibitory synapses prevails. It is assumed that the value of the regulated body temperature will be set at the temperature value (set point), at which the signal flows from the TPN will be equivalent to the flows of signals of the opposite sign from the TPN. Under normal conditions, in a healthy person, the temperature value, or set point value, is the one at which the equivalence of the receipt of excitatory and inhibitory signal flows to the effector neurons from the SC and TNN is achieved, and is about 37 ° C. At this temperature value, the activity of effector neurons is close to zero, but when the local temperature of the preoptic area changes or the afferent influx from peripheral thermoreceptors changes, such a change in the activity of effector neurons occurs, which is necessary to trigger thermoregulatory reactions and maintain body temperature at the level specified for a given organism .

The maturation of the central hypothalamic mechanisms of thermoregulation in children can be judged by the establishment of the correct daily rhythm of body temperature, which occurs by 1.5-2 months of age. Hypoxia, intracranial trauma, infections affecting the central nervous system, as well as its anomalies, can cause dysfunction of the central thermoregulatory apparatus.

Body temperature. The fetus, located in the mother's womb at a relatively constant body temperature, does not need its own thermoregulation. The heat that is generated by the fetal body is transferred through the placenta to the mother's blood, and the temperature of the blood flowing from the fetus to the placenta is 0.3-0.5 ° C higher than the blood flowing to the fetus. The value of fetal TP before birth is about 10-15% of the maternal TP.

Body temperature (rectal) in a healthy newborn is 37.7-38.2 °C, which is 0.1-0.6 "C higher than the mother's body temperature. In children born prematurely, born with asphyxia, or severely injured at birth, there is a significant decrease in body temperature, which can persist for several days. A decrease in temperature to 35 "C and below, later returning to normal -

This level and significant subsequent fluctuations in body temperature usually indicate a failure of thermoregulatory mechanisms.

Over the next few hours after birth, body temperature in healthy newborns drops by 1.5-2 °C. The degree of decrease in body temperature is influenced by the weight of the child, the size of his body, the amount of vernix, and the conditions for caring for the newborn. In healthy children, body temperature soon begins to rise and after 12-24 hours reaches 36-37 °C. Axillary temperature at birth is about 37.2 °C, after 2-3 hours it drops to 35.7 °C, by the 4th-5th hour it gradually rises to 36.5 °C, and by the 5th day of life - to 37 "C. Usually, in the first days of life, a healthy newborn experiences temperature instability and rapid changes during swaddling and after feeding. Over the following days, the body temperature in newborns remains unstable and only gradually (by 1.5-3 months) the temperature curve is established , characteristic of healthy infants. For a long time, the body temperature in children usually remains 0.3-0.4 "C higher than in adults, and only gradually reaches the level of adults. A decrease in temperature in the first hours after birth is called transient hypothermia of newborns. It is caused by the effect of a lower ambient temperature than in the womb and the immaturity of thermoregulation mechanisms. In children born physiologically immature and (or) premature, as well as in patients, more pronounced hypothermia is observed, which persists for several days.

Rectal temperature in children is usually 0.3-0.5 °C higher than skin temperature, measured in the armpit or groin area. After physical exercise, especially after running, long walks and other activities, the temporary increase in rectal temperature in children is greater than that in the axillary, and the temperature difference in these areas can reach 1 °C or more. In this case, in children there is a local rather than a general increase in body temperature. The higher rectal temperature is explained by abundant blood flow in this area, the proximity of large muscle masses that produce heat, and heat production by bacterial microflora.

The pattern of daily fluctuations in body temperature, or circadian rhythm, varies among children, but is relatively constant within an individual. The circadian rhythm is absent in newborns and young children and is established after the second year of life. In children it is more pronounced than in adults. The lowest body temperature is observed around 3 a.m., and the highest - from 5 to 6 p.m. The difference between the highest and lowest points of the temperature cycle in children is greater than in

adults. This difference in children can reach 1.4 °C. Daily temperature fluctuations are more significant in girls than in boys. The range of temperature fluctuations during the day at a stable ambient temperature in the first days of life is about 0.3 "C, by 2-3 months it increases to 0.6 °C and by 3-5 years - to 1 °C. The magnitude of temperature fluctuations body depends not only on age, but also on environmental temperature, physical activity, emotional state of the child, quality and quantity of food taken, functional state of the endocrine system, as well as other factors affecting basal metabolism, physical activity, vascular tone.Clinical significance The circadian rhythm is multifaceted. Knowledge of normal daily temperature changes helps the doctor to avoid misinterpreting the causes of a moderate physiological increase in evening temperature and perceiving it as a manifestation of hyperthermia or fever. The same applies to the current discussions about “subnormal temperature” in the early morning hours.

Cyclic daily fluctuations in body temperature in a healthy child are established by 1.5-2 months of life, which coincides in time with the formation of daily rhythms of heart rate and respiratory rate. In premature infants, the daily cycle of temperature is established much later than in full-term infants. The preservation of a normal circadian rhythm of temperature in children with brain diseases may indicate that the central mechanisms of thermoregulation are not damaged. At the same time, if no other reasons have been identified to explain the child’s lack of circadian rhythm, this allows one to suspect the presence of a false fever.

The relative insufficiency of heat production in newborns, and especially premature infants, requires the creation of an optimal temperature environment for them - a thermoneutral zone. Its boundaries are the range of air temperature surrounding the child, at which normal body temperature is maintained with minimal tension on the TP mechanisms. If for healthy naked newborns born at term, the boundaries of the thermoneutral zone are 32-35 ° C, then under these conditions for a very premature baby - 35-36 "C. For swaddled newborns, the temperature boundaries of this zone shift to 23-26 ° C and 30-33 ° C, respectively. By the age of one month, the temperature indicators of the thermoneutral zone shift down by 1.5-2 ° C, and the width of their range increases by 0.3-0.5 ° C.

In healthy newborn children, there is practically no decrease in body temperature below 36-36.1 °C. A decrease in temperature below this level usually reflects a failure of energy metabolism and is observed, as a rule, with malnutrition of the I-III degree, severe cardiac and vascular failure, insufficiency of liver and kidney function, decreased function of the thyroid gland, adrenal glands, hypoglycemia and other serious diseases. Body temperature drops sharply during anaphylactic shock and collapse of allergic origin.

Changes in body temperature in children can be caused by various reasons. Prolonged exposure to cold or heat may be uncompensated by insufficiently mature thermoregulation mechanisms and lead to a significant increase (exogenous hyperthermia) in body temperature or a decrease (exogenous hypothermia), which often occurs in premature and immature children.

Newborns easily overheat when the air temperature rises, which is due to their low body weight, the proximity of the temperature of the thermal indifferent zone and body temperature, and the low functional activity of the sweat glands. Overheating is also caused by excessively restricting heat transfer by clothing.

When exposed to low air temperatures in newborns, heat production increases, but the intensity of this reaction is often insufficient to maintain normal body temperature, especially with prolonged exposure to cold. The maximum increase in heat production in newborns does not exceed twice the value of the basal metabolism (in an adult, heat production during cooling can increase for a short time by 3-4 times).

Thus, among the most important features of thermoregulation in newborns we can highlight: a higher level of heat transfer in relation to heat production; limited ability to increase heat transfer during overheating, as well as to increase heat production during cooling; inability to respond with a feverish temperature reaction due to the weak sensitivity of hypothalamic neurons to the action of leukocyte and other endopyrogens and the high concentration of arginine vasopressin in the blood, which reduces body temperature. A feature of thermoregulation in newborns is the absence of reactions of increased thermoregulatory tone and cold shivering when body temperature decreases. When rapidly cooling, they exhibit a variety of uncoordinated movements, accompanied by screaming. This reaction serves as a signal to the mother to eliminate exposure to cold.