Hypothermia, definition of the concept, classification. Mechanisms of compensation during physical hypothermia. Pathophysiological rationale for the use of artificial hypothermia in the clinic. Hypothermia symptoms and treatment

– a pathological condition of the human body caused by the action of low temperatures that exceed in intensity the internal reserves of the thermoregulation system. During hypothermia, the temperature of the body's core ( vessels and organs abdominal cavity ) decreases below optimal values. The metabolic rate decreases, and self-regulation of all body systems fails. In the absence of timely and proportionate care, the lesions progress and can ultimately lead to death.


Interesting Facts

• When the body temperature drops below 33 degrees, the victim ceases to realize that he is freezing and cannot help himself.
• Rapidly warming a hypothermic patient can lead to his death.
• When the skin temperature is less than 10 degrees, its cold receptors are blocked and stop alerting the brain about the danger of hypothermia.
• According to statistics, every third person who died from hypothermia was intoxicated.
• Any working skeletal muscle warms up by 2 – 2.5 degrees.
• The most active areas of the brain are warmer than passive ones, on average, by 0.3 - 0.5 degrees.
• Shivering increases heat production by 200%.
• The “point of no return” is considered to be a body temperature of less than 24 degrees, at which it is almost impossible to return a frostbite victim to life.
• In newborns, the thermoregulation center is underdeveloped.

How is body temperature regulated?

Regulation of body temperature is a complex multi-level process with a strict hierarchy. The main regulator of body temperature is the hypothalamus. This part of the brain receives information from thermoreceptors throughout the body, evaluates it and gives instructions to the intermediary organs for action to implement this or that change. The middle, medulla oblongata and spinal cord exercise secondary control of thermoregulation. There are many mechanisms by which the hypothalamus produces the desired effect. The main ones will be described below.

In addition to thermoregulation, the hypothalamus performs many other functions, no less important functions human body. However, to understand the causes of hypothermia, in the future, special attention will be paid only to its thermoregulatory function. To clearly explain the mechanisms of body temperature regulation, it is necessary to trace the development of the body’s response to low temperatures, starting with the excitation of cold receptors.

Receptors

Low Temperature Information environment perceived by special cold receptors. There are two types of cold receptors - peripheral ( located throughout the body) and central ( located in the hypothalamus).

Peripheral receptors
There are approximately 250 thousand receptors in the thickness of the skin. Approximately the same number of receptors are found in other tissues of the body - in the liver, gall bladder, kidneys, blood vessels, pleura, etc. Skin receptors are most densely located on the face. With the help of peripheral thermoreceptors, information is collected about the temperature of the environment in which they are located, and a shift in the temperature of the “core” of the body is prevented.

Central receptors
There are significantly fewer central receptors - on the order of several thousand. They are located exclusively in the hypothalamus and are responsible for measuring the temperature of the blood flowing to it. When central receptors are activated, more intense heat generation reactions are triggered than when peripheral receptors are activated.

Both central and peripheral receptors respond to changes in environmental temperature in the range from 10 to 41 degrees. At temperatures outside these limits, the receptors are blocked and stop functioning. An environmental temperature of 52 degrees leads to the destruction of receptors. The transmission of information from receptors to the hypothalamus is carried out through nerve fibers. When the temperature of the environment decreases, the frequency of impulses sent to the brain increases, and when the temperature rises, it decreases.

Hypothalamus

The hypothalamus is a relatively small part of the brain, but it performs exclusively important role in the regulation of the constancy of the internal environment of the body. Regarding its thermoregulatory function, it should be said that it is conventionally divided into two sections - anterior and posterior. The anterior part of the hypothalamus is responsible for activating heat transfer mechanisms, and the posterior part is responsible for activating heat generation mechanisms. There is also a special group in the hypothalamus nerve cells, which summarizes all received thermoreceptor signals and calculates the force of the necessary impact on the body systems to maintain the required body temperature.

When hypothermia occurs, the hypothalamus activates heat production reactions and stops heat loss processes through the following mechanisms.

Heat generation mechanisms

Heat formation, on the scale of the entire organism, is subject to a single rule - the higher the metabolic rate in any organ, the more heat it produces. Accordingly, in order to increase heat generation, the hypothalamus accelerates the work of all organs and tissues. Thus, the working muscle warms up by 2 - 2.5 degrees, the parotid gland - by 0.8 - 1 degree, and actively working areas of the brain - by 0.3 - 0.5 degrees. Acceleration of metabolic processes is carried out by influencing the autonomic nervous system.

The following heat generation mechanisms are distinguished:

• strengthening muscle work;
• increase in basal metabolism;
• specific dynamic effect of food;
• acceleration of hepatic metabolism;
• increased heart rate;
• increase in circulating blood volume;
• acceleration of the functioning of other organs and structures.

Strengthening muscle work
At rest, striated muscles produce on average 800–1000 kcal per day, which is 65–70% of the heat generated by the body. The body's response to cold is shivering or chills, in which muscles involuntarily contract at a high frequency and low amplitude. Shivering increases heat production by 200%. Walking increases heat generation by 50 - 80%, and heavy walking physical labor– by 400 – 500%.

Increase in basal metabolism
Basic metabolism is a value corresponding to the average rate of all chemical reactions body. The body's response to hypothermia is to increase basal metabolism. Basic metabolism is not synonymous with metabolism, since the term “metabolism” is characteristic of a single structure or system. In some diseases, the basal metabolic rate may decrease, which ultimately leads to a decrease in comfortable body temperature. The rate of heat generation in such patients is much lower than in other people, which makes them more susceptible to hypothermia.

Specific dynamic action of food
Eating food and digesting it require the body to release some additional amount of energy. Part of it is converted into thermal energy and is included in the general process of heat generation, although only slightly.

Acceleration of liver metabolism
The liver is compared to the chemical factory of the body. Thousands of reactions occur in it every second, accompanied by the release of heat. For this reason, the liver is the “hottest” internal organ. The liver produces an average of 350–500 kcal of heat per day.

Increased heart rate
Being a muscular organ, the heart, like other muscles of the body, generates heat when working. It produces 70–90 kcal of heat per day. When hypothermia occurs, the heart rate increases, which is accompanied by an increase in the amount of heat produced by the heart to 130 - 150 kcal per day.

Increased circulating blood volume
The human body circulates from 4 to 7 liters of blood, depending on body weight. 65 - 70% of the blood is constantly in motion, and the remaining 30 - 35% is in the so-called blood depot ( unused blood reserve needed for emergency situations, such as heavy physical work, lack of oxygen in the air, bleeding, etc.). The main blood depots are veins, spleen, liver, skin and lungs. With hypothermia, as indicated above, the basal metabolism increases. An increase in basal metabolism requires more oxygen and nutrients. Since blood is their carrier, its quantity should increase in proportion to the increase in basal metabolism. Thus, blood from the depot enters the bloodstream, increasing its volume.

Acceleration of the functioning of other organs and structures
The kidneys produce 70 kcal of heat per day, the brain - 30 kcal. The breathing muscles of the diaphragm, working continuously, supply the body with an additional 150 kcal of heat. In hypothermia frequency breathing movements increases from one and a half to two times. Such an increase will lead to an increase in the amount of thermal energy released by the respiratory muscles to 250 - 300 kcal per day.

Mechanisms of heat loss

In conditions of low temperatures, the body's adaptive reaction is to minimize the volume of heat loss. To accomplish this task, the hypothalamus, as in the previous case, acts by influencing the autonomic nervous system.

Mechanisms for reducing heat loss:

• centralization of blood circulation;
• increase in subcutaneous fat;
• reduction of open body area;
• reduction of heat loss by evaporation;
• skin muscle reaction.

Centralization of blood circulation
The body is conventionally divided into “core” and “shell”. The “core” of the body is all the organs and vessels of the abdominal cavity. The core temperature practically does not change, since maintaining its constancy is necessary for the correct functioning of vital organs. The “shell” refers to the tissues of the limbs and the entire skin covering the body. Passing through the “shell,” the blood cools, giving energy to the tissues through which it flows. The farther a part of the body is from the “core,” the colder it is. The rate of heat loss directly depends on the amount of blood passing through the “shell”. Accordingly, during hypothermia, to reduce heat loss, the body reduces blood flow to the “shell”, directing it to circulate only through the “core”. For example, at a temperature of 15 degrees, the blood flow in the hand decreases by 6 times.

With further cooling of the peripheral tissue, the blood flow in it may stop completely due to spasm blood vessels. This reflex is certainly beneficial for the body as a whole, as it is aimed at preserving life. However, for parts of the body deprived of the necessary blood supply, it is negative, since with prolonged spasm of blood vessels combined with low temperature, frostbite can occur.

Increase in subcutaneous fat
When staying in cold climates for a long time human body rebuilt in such a way as to reduce heat loss. The total mass of adipose tissue increases and is redistributed throughout the body more evenly. Its main part is deposited under the skin, forming a layer 1.5 - 2 cm thick. A smaller part is distributed throughout the body and settles between the muscle fascia in the greater and lesser omentum, etc. The essence of this change is that adipose tissue conducts heat poorly, ensuring its preservation inside the body. In addition, adipose tissue does not require such high oxygen consumption. This provides it with an advantage over other tissues in conditions of oxygen deficiency due to prolonged spasm of the vessels feeding it.

Reducing exposed body area
The rate of heat loss depends on the temperature difference and the area of ​​contact of the body with the environment. If it is not possible to influence the temperature difference, then you can change the contact area by taking a more closed position. For example, in cold weather animals curl up into a ball, reducing the area of ​​contact with the environment, and in hot weather, on the contrary, they strive to increase it, straightening up as much as possible. Likewise, a person, falling asleep in a cold room, subconsciously pulls his knees to his chest, taking a more energy-efficient pose.

Reducing heat loss by evaporation
The body loses heat when water evaporates from the surface of the skin or mucous membranes. Scientists have calculated that the evaporation of 1 ml of water from the human body leads to a loss of 0.58 kcal of heat. An adult loses an average of 1400–1800 ml of moisture per day through evaporation during normal physical activity. Of these, 400 - 500 ml evaporates through Airways, 700 – 800 ml by perspiration ( imperceptible seepage) and 300 – 500 ml - through sweat. In conditions of hypothermia, sweating stops, breathing slows down and vaporization in the lungs decreases. Thus, heat loss is reduced by 10 - 15%.

Skin muscle response goose pimples )
In nature, this mechanism occurs very often and consists of tension in the muscles that lift the hair follicles. As a result, the undercoat and cellularity of the coat increase, and the layer of warm air around the body thickens. This results in improved thermal insulation, since air is a poor conductor of heat. In humans, during evolution, this reaction has been preserved in a rudimentary form and has no practical value.

Causes of hypothermia

Factors influencing the likelihood of hypothermia:

• weather;
• quality of clothes and shoes;
• diseases and pathological conditions of the body.

Weather

Parameters that influence the rate of heat loss by the body are:

• ambient temperature;
• air humidity;
• wind power.

Ambient temperature
Ambient temperature is the most significant factor in hypothermia. In physics, in the section of thermodynamics, there is a pattern that describes the rate of decrease in body temperature depending on the temperature of the environment. In essence, it comes down to the fact that the greater the temperature difference between the body and the environment, the more intense the heat exchange occurs. In the context of hypothermia, this rule would sound like this: the rate of heat loss by the body will increase as the ambient temperature decreases. However, the above rule will only work if a person is in the cold without clothes. Clothing greatly reduces heat loss from the body.

Air humidity
Atmospheric humidity affects the rate of heat loss in the following way. As humidity increases, the rate of heat loss increases. The mechanism of this pattern is that at high humidity, a layer of water invisible to the eye forms on all surfaces. The rate of heat loss in water is 14 times higher than in air. Thus, water, being a better conductor of heat than dry air, will transfer body heat to the environment faster.

Wind power
Wind is nothing more than the unidirectional movement of air. In a windless environment, a thin layer of heated and relatively still air forms around the human body. Under such conditions, the body spends a minimum of energy to maintain a constant temperature of this air shell. In windy conditions, the air, barely warmed up, moves away from the skin and is replaced by colder air. To maintain optimal body temperature, the body has to speed up the basal metabolism and activate additional heat generation reactions, which ultimately requires large amounts of energy. At a wind speed of 5 meters per second, the rate of heat transfer increases approximately twofold, at 10 meters per second - fourfold. Further growth occurs in geometric progression.

Quality of clothes and shoes

As mentioned above, clothing can greatly reduce heat loss from the body. However, not all clothing protects against the cold equally effectively. The main influence on the ability of clothing to retain heat is the material from which it is made, and correct selection size of item or shoe.

The most preferred material in the cold season of the year is natural wool and fur. In second place are their artificial analogues. The advantage of these materials is that they have high cellularity, in other words, they contain a lot of air. Being a poor conductor of heat, air prevents unnecessary energy loss. The difference between natural and faux fur is that the cellularity of natural material is several times higher due to the porosity of the fur fibers themselves. A significant disadvantage of synthetic materials is that they contribute to the accumulation of moisture under clothing. As stated earlier, high humidity increases the rate of heat loss, promoting hypothermia.

The size of shoes and clothes should always correspond to body parameters. Tight clothing stretches over the body and reduces the thickness of the layer of warm air. Tight shoes cause compression of the blood vessels that feed the skin, subsequently leading to frostbite. Patients with swollen feet are advised to wear shoes made of soft material that can stretch without compressing the limbs. The sole must be at least 1 cm thick. Big sizes clothes and shoes, on the contrary, do not fit tightly enough to the body, form folds and crevices through which warm air escapes, not to mention the fact that they are simply uncomfortable to wear.

Diseases and pathological conditions of the body

Diseases and pathological conditions that contribute to the development of hypothermia:

• cirrhosis of the liver;
• cachexia;
• state of alcoholic intoxication;
• bleeding;
• traumatic brain injury.

Heart failure
Heart failure is a serious disease in which the pumping function of the heart muscle is affected. The rate of blood flow throughout the body decreases. As a result, the time the blood stays at the periphery increases, which leads to stronger cooling. With heart failure, swelling often forms, starting from the feet and eventually rising higher, up to chest. Swelling further worsens blood circulation in the extremities and leads to even greater cooling of the blood. To maintain the required body temperature, the body is forced to constantly use heat generation mechanisms, even at normal ambient temperatures. However, when it decreases, the mechanisms of thermogenesis are depleted, and the rate of drop in body temperature increases sharply, introducing the patient into a state of hypothermia.

Cirrhosis of the liver
This disease is the result of long-term replacement of functional liver tissue with non-functional connective tissue. With a long course of the disease, free fluid accumulates in the abdominal cavity, the volume of which can reach 15–20 liters. Since this fluid is located within the body, additional resources must be constantly expended to maintain its temperature and some of the heat generation mechanisms must be involved. The abdomen of such patients is tense. Internal organs and blood vessels are subject to compression. When the inferior vena cava is compressed, swelling rapidly develops lower limbs. As mentioned earlier, edema leads to additional cooling of the blood, requiring additional efforts of the heat generation system. As the ambient temperature decreases, the heat generation mechanisms will no longer cope with their task, and the patient’s temperature will begin to drop steadily.

Addison's disease
Addison's disease is adrenal insufficiency. Normally, the adrenal cortex produces three types of hormones - crystalloids ( aldosterone), glucocorticoids ( cortisol) and androgens ( androsterone). If there is insufficient amount of two of them in the blood ( aldosterone and cortisol) blood pressure decreases. A decrease in blood pressure leads to a slowdown in the speed of blood flow throughout the body. Blood passes one circle through the human body over a longer period of time, cooling more strongly. In addition to the above, a lack of glucocorticoids leads to a decrease in the body's basal metabolism, a decrease in the rate of chemical reactions accompanied by the release of energy. As a result, the core produces less heat, which, coupled with greater cooling of the blood, leads to a significant risk of hypothermia, even at moderately low temperatures.

Hypothyroidism
Hypothyroidism is an endocrine disease caused by insufficient production of thyroid hormones. Like glucocorticoids, hormones thyroid gland (triiodothyronine and thyroxine) are responsible for the regulation of many biological processes in the human body. One of the functions of these hormones is to maintain a uniform rate of reactions accompanied by the release of heat. When thyroxine levels decrease, body temperature decreases. The more pronounced the hormone deficiency, the lower constant temperature bodies. Such patients are not afraid of high temperatures, but in the cold they quickly become hypothermic.

Cachexia
Cachexia is a state of extreme exhaustion of the body. It develops over a relatively long time ( weeks and even months). The causes of cachexia are oncological diseases, AIDS, tuberculosis, cholera, long-term malnutrition, extremely high physical exercise etc. With cachexia, the patient’s weight is greatly reduced, mainly due to fat and muscle tissue. This is what determines the mechanism for the development of hypothermia in this pathological condition. Adipose tissue is a kind of thermal insulator of the body. With its deficiency, the rate of loss of body temperature increases. In addition, adipose tissue, when broken down, produces 2 times more energy than any other tissue. In its absence, the body has to use proteins for its own heating - the “building blocks” from which our body is built.

The above situation can be compared with heating a residential building by oneself. Muscles are the main structure of the body that produces thermal energy. Their share in heating the body is 65–70% at rest, and up to 95% during intensive work. When decreasing muscle mass The level of heat production by the muscles also drops. Summarizing the effects obtained, it turns out that a decrease in the thermal insulating function of adipose tissue, its absence as the main source of heat generation reactions and a decrease in mass muscle tissue leads to an increased risk of hypothermia.

State of alcoholic intoxication
This condition is a consequence of the presence of a certain amount of alcohol in a person’s blood, which can cause a certain biological effect. According to scientists, the minimum amount alcoholic drink, necessary for the beginning of the development of inhibition processes of the cerebral cortex, ranges from 5 to 10 ml of pure alcohol ( 96% ), and for dilating the blood vessels of the skin and subcutaneous fat, it ranges from 15 to 30 ml. For the elderly and children this measure half as much. When peripheral vessels dilate, a deceptive sensation of warmth is created.

It is with this effect of alcohol that the myth is associated that alcohol helps to warm the body. By dilating blood vessels, alcohol prevents the manifestation of the centralization reflex of blood circulation, developed over millions of years of evolution, and designed to preserve human life in low temperatures. The catch is that the feeling of warmth is caused by the flow of warm blood from the torso to the cold skin. The incoming blood quickly cools and returning to the “core” greatly reduces the overall body temperature. If a person in a state of severe alcoholic intoxication falls asleep on the street at sub-zero temperatures, then most often he wakes up in a hospital room with frostbitten limbs and bilateral pneumonia, or does not wake up at all.

Bleeding
Bleeding is the flow of blood from the bloodstream into the external environment or into the body cavity. The mechanism of action of blood loss leading to hypothermia is simple. Blood is a liquid medium that, in addition to oxygen and nutrients, transfers thermal energy to organs and tissues. Accordingly, the body's loss of blood is directly proportional to the loss of heat. Slow or chronic bleeding is tolerated much better by humans than acute bleeding. With prolonged slow bleeding, the patient can survive even after losing half of his blood.

Acute blood loss is more dangerous, since it does not have time to activate compensatory mechanisms. The severity of the clinical picture of acute bleeding depends on the volume of blood loss. Blood loss of 300–500 ml is tolerated by the body almost imperceptibly. Blood reserves are released, and the deficiency is completely compensated. With blood loss of 500 to 700 ml, the victim experiences dizziness and nausea, strong feeling thirst. There is a need to take a horizontal position to alleviate the condition. Blood loss of 700 ml - 1 liter is manifested by a short-term loss of consciousness. When a victim falls, his body assumes a horizontal position, blood is directed to the brain, and the person comes to his senses on his own.

The most dangerous is acute blood loss of more than 1 liter, especially in conditions of negative temperatures. The patient may lose consciousness for a period of half an hour to several hours. While he is in unconscious, all thermoregulation mechanisms are turned off. Thus, the rate of drop in body temperature of an unconscious person is equal to the rate of drop in body temperature of a corpse, which on average equals one degree per hour ( in the absence of wind and normal air humidity). At this rate, a healthy person will reach the first degree of hypothermia in 3, the second in 6–7 and the third in 9–12 hours.

Traumatic brain injury
With a traumatic brain injury, as with heavy bleeding, there is a risk of loss of consciousness. The danger of hypothermia during loss of consciousness is described in detail above.

Degrees of hypothermia

Classification of stages of hypothermia depending on clinical manifestations

Stage	Development mechanism	External manifestations
Dynamic	Spasm of peripheral vessels. Compensatory activation of all heat generation mechanisms. Excessive stress activation of the sympathetic autonomic nervous system.	Pale skin, goose bumps. Strong muscle tremors. The ability to move independently is preserved. Lethargy and drowsiness, slow speech, slow reaction to stimuli. Rapid breathing and heart rate.
Stuporous	Depletion of the body's compensatory reactions. Deterioration of peripheral blood supply, up to its absence. Slowing down metabolic processes in the brain. Partial separation of the activity of the cortex and subcortical zone. Suppression of the brain centers of breathing and heartbeat.	Paleness of the skin. Ears, nose, cheeks, limbs become bluish in color. Associated frostbite of 1 – 2 degrees. No muscle tremors. Muscle stiffness, up to the inability to straighten the limb. Boxer pose. Superficial coma. The pupils are moderately dilated, the reaction to light is positive. Reaction only to strong painful stimuli. Breathing slows down and becomes shallow. Decrease in heart rate.
Convulsive	Complete depletion of compensatory mechanisms. Damage to peripheral tissues due to prolonged lack of blood supply. Extreme deterioration of metabolic processes in the brain. Complete separation of the work of different parts of the brain. The appearance of foci of convulsive activity. Severe depression of the brain centers of breathing and heartbeat. Slowdown of the conduction system of the heart.	Pale blue skin. Associated frostbite of 3 – 4 degrees of protruding parts of the body. Severe muscle rigor. Deep coma. The pupils are maximally dilated. The reaction to light is absent or extremely weak. There is no reaction to any stimuli. Attacks of generalized convulsions are repeated every 15 to 30 minutes. Lack of rhythmic breathing. Reducing heart rate to 20 - 30 per minute. Rhythm disturbances. At 20 degrees, breathing and heartbeat usually stop.

Due to the fact that the stages of clinical manifestations of hypothermia do not always correspond to certain temperature limits, there is a classification of degrees of hypothermia depending on body temperature that is of secondary clinical information value.

Classification of degrees of hypothermia, depending on body temperature

Symptoms of hypothermia

In this section, the symptoms of hypothermia are selected in such a way that the victim or first aid provider can roughly determine the severity of hypothermia without specialized equipment.

Symptoms of hypothermia in order of appearance

Symptom	Reason for appearance
Pale skin	Spasm of peripheral vessels to reduce heat transfer.
"Goose pimples	Vestigial defensive reaction in the form of tension in the muscles that lift the hair follicle. In animals it helps to increase the undercoat layer. It has no effect in humans.
Shiver	Rhythmic contractions of muscle fibers, characterized by high frequency and low amplitude. Lead to an increase in heat production up to 200%.
Tachycardia	A compensatory reaction of the body to a threat caused by excessive tone of the sympathetic nervous system and an increase in the level of adrenaline in the blood.
Rapid breathing	At low temperatures, the body is forced to speed up the basal metabolism and activate heat production systems. These processes require increased oxygen delivery, which is carried out through increased breathing.
Weakness, drowsiness	Cooling the blood leads to slow cooling of the brain. Cooling of the reticular formation, a special structure of the brain, leads to a decrease in the tone of the body, which is felt by a person as lethargy, weakness and a craving for sleep.
Rigor	Freezing of a muscle causes it to lose its ability to excite. In addition, the rate of metabolic processes in it drops to almost zero. Intracellular and intercellular fluid crystallize.
Pain	The appearance of pain is associated with the process of tissue hardening during freezing. When in contact with rough tissue, pain receptors are excited much more strongly than when in contact with soft cloth. Increased impulses of the excited nerve create a sensation of pain in the brain.
Slow reaction and speech	The slowing of speech is associated with a decrease in the activity of the speech center of the brain due to its cooling. The slowdown in reaction is caused by a decrease in the speed of transmission of the nerve impulse along reflex arc (the path from its formation to the effects caused by it).
Decreased heart rate	The cause of this symptom is a decrease in the activity of the heartbeat center located in the medulla oblongata.
Decreased respiratory rate	This phenomenon occurs due to a decrease in the activity of the respiratory center located in the medulla oblongata.
Spasm of the masticatory muscles (trismus)	This symptom The reason for its occurrence is similar to rigor of other muscles of the body, but it brings much more trouble. Trismus usually develops in the stuporous and convulsive stages of frostbite. Carrying out resuscitation measures involves inserting a plastic tube into the patient’s airway, but due to trismus, this manipulation cannot be performed.
Convulsions	When the temperature of the brain drops below 28 degrees, the synchronous functioning of all its departments is disrupted. Foci of asynchronous impulses are formed, characterized by high convulsive activity.
Pathological breathing	This type of breathing is represented by periods of increasing and decreasing depth of breathing, interrupted by long pauses. The effectiveness of such breathing is extremely low. This indicates cold damage to the respiratory center located in the brain stem and means a poor prognosis for the patient.
Heart rhythm disturbances	The first reason is the inhibition of the heartbeat center mentioned above. The second reason is disruption of the processes of excitation and conduction of nerve impulses in the heart itself. As a result, additional foci of excitation arise, leading to arrhythmias, and impulse conduction blocks leading to asynchronous contraction of the atria and ventricles. Any of these rhythm disturbances can lead to cardiac arrest.
Lack of breathing and heartbeat	This symptom develops when the body temperature is below 20 degrees. It is a consequence of extreme inhibition of the corresponding centers of the brain. Requires chest compressions and artificial respiration.

First aid for hypothermia

It is extremely important, before starting first aid, to determine the severity of hypothermia and decide whether there is a need to call an ambulance.

Indications for hospitalization for hypothermia:

• stuporous or convulsive stage of general hypothermia;
• poor response to first aid even during the dynamic stage of hypothermia;
• concomitant frostbite of body parts of III and IV degrees;
• concomitant frostbite of body parts I and II degrees in combination with vascular diseases lower extremities or diabetes mellitus.

After assessing the severity of the victim and, if necessary, calling an ambulance, the patient should be given first aid.

Algorithm for action in case of hypothermia:

1. Stop the victim's contact with the cold environment. It is necessary to take him to a warm room, remove frozen and wet clothes and change into clean, dry clothes.
2. Offer the victim any warm drink ( tea, coffee, broth). It is important that the temperature of the drink does not exceed body temperature by more than 20 - 30 degrees, otherwise the risk of burns to the oral mucosa, esophagus and stomach increases.
3. Wrap the patient in any thermal insulating material. The most effective in this case will be special blankets made of thick foil. In their absence, you can use cotton blankets or any other.
4. Avoid excessive movement of the victim from place to place, as unnecessary movements can cause pain and contribute to heart rhythm disturbances.
5. Body massage in the form of light rubbing promotes heat generation through friction, and also accelerates the restoration processes of the skin and subcutaneous tissue. However, rough massage can provoke the heart rhythm disturbances mentioned above.
6. Good therapeutic effect bring warm baths. The water temperature at the beginning of the procedure should be equal to body temperature or exceed it by 2 - 3 degrees. Then you should slowly increase the water temperature. The temperature rise should not exceed 10 - 12 degrees per hour. It is extremely important to monitor the patient’s condition during active warming in a warm bath, since with rapid warming, there is a possibility of developing “Afterdrop” syndrome, in which the blood pressure drops sharply. arterial pressure, up to a state of shock.

First aid medications for hypothermia:

• Antispasmodics. This group of medications should be used only after the victim has begun to warm up. Prescribing them to a patient under the influence of cold will sharply worsen his condition. The rate of decrease in temperature will increase and an earlier decrease in respiratory rate will develop than would occur without the prescription of the drug. Papaverine 40 mg 3 – 4 times a day is used as antispasmodics; drotaverine ( no-shpa) 40 – 80 mg 2 – 3 times a day; mebeverine ( duspatalin) 200 mg 2 times a day.
• Painkillers. Pain is a factor that in itself contributes to the worsening of any disease. The presence of pain during hypothermia is a direct indication for the use of painkillers. Analgin 500 mg 2-3 times a day is used as an analgesic for hypothermia; dexketoprofen 25 mg 2 – 3 times a day; ibuprofen 400 mg 4 times a day.
• Nonsteroidal anti-inflammatory drugs (NSAIDs). This group of drugs is used to prevent inflammatory processes after warming up the victim, as well as to reduce the intensity of pain. For stomach and duodenal ulcers, this group of drugs is used with caution. The following non-steroidal anti-inflammatory drugs are used to treat hypothermia: acetylsalicylic acid ( aspirin) 250 – 500 mg 2 – 3 times a day; nimesulide 100 mg 2 times a day; ketorolac ( ketanov) 10 mg 2 – 3 times a day.
• Antihistamines. This group of drugs is actively used for allergic diseases. However, they are no less effective in fighting any inflammatory process of non-bacterial origin, and accordingly are suitable for reducing the symptoms of hypothermia. The most common antihistamines are: suprastin 25 mg 3 – 4 times a day; clemastine 1 mg 2 times a day; Zyrtec 10 mg once a day.
• Vitamins. Most effective drug in case of hypothermia is vitamin C. It positive action consists of strengthening the walls of blood vessels damaged by low temperatures. It is used 500 mg 1 – 2 times a day.

The above drugs are given in doses corresponding to an adult without significant impairment of the excretory function of the kidneys. When adverse reactions For any of the medications taken, you must immediately seek qualified medical help.

Treatment of hypothermia

Treatment of hypothermia is an extremely difficult task, as it requires a broad approach to the pathology. With hypothermia, disruptions in the functioning of all body systems occur, and assistance must be provided in a comprehensive manner, otherwise treatment will lead to nothing. It is also important to note that treatment of hypothermia at home is only permissible for the first ( dynamic) its stages. In case of stuporous and convulsive stages, treatment in a hospital department is necessary intensive care.

Attempts to treat a patient with hypothermia of the second and third stages at home are doomed to failure for at least three reasons. Firstly, at home there is no special equipment and laboratory in order to constantly monitor the dynamics of changes in the body’s vital signs. Secondly, the condition of such patients requires intensive supportive therapy, in the absence of which the patient cannot recover using only his own body. Thirdly, the hypothermic patient's condition tends to sharp deterioration, which in the absence of appropriate assistance will lead to his quick and inevitable death.

Once in the hospital emergency room, a victim of hypothermia is immediately sent to the intensive care unit ( resuscitation). Basic therapeutic measures are divided into two main areas - warming the patient and correcting vital signs of the body.

Warming the victim:

• Eliminate contact of frozen clothing with the victim’s body.
• Wrapping the victim in a thermal insulating material, such as a special “space” blanket, the main component of which is foil.
• Place the patient under a lamp with dosed infrared radiation.
• Covering the patient with heating pads with warm water. The water temperature in them should not exceed body temperature by more than 10 - 12 degrees.
• Immersion in a warm bath. The water temperature at the beginning of the procedure is 2–3 degrees higher than body temperature. Subsequently, the water temperature rises by 8 - 10 degrees per hour.
• Applying heat to the projections of large blood vessels.
• Intravenous administration of warm infusion solutions, the temperature of which should not exceed 40 - 42 degrees.
• Gastric lavage with warm water ( 40 – 42 degrees). If there is spasm of the masticatory muscles and it is impossible to insert the probe through the mouth, diazepam is injected into the muscles of the floor of the mouth, and then the probe is reinserted. If there is spasm in the masticatory muscles, you can insert a probe through the nose ( nasogastric tube), however with great caution, as the risk of vomiting and stomach contents entering the respiratory tract significantly increases.

Correction of vital signs:

• Oxygenation with humidified oxygen. The percentage of oxygen in the inspired air should be selected so that the saturation ( saturation) blood oxygen was more than 95%.
• Maintaining blood pressure within 80/60 – 120/80 mmHg. For low blood pressure, atropine 0.1% - 1 ml is administered intravenously ( diluted with 10 – 20 ml saline); prednisolone 30 – 60 mg; dexamethasone 4 – 8 mg.
• Correction of the electrolyte composition of the blood - Ringer-Lock solution, Ringer-lactate, dextran-40, dextran-70, etc.
• Correction of blood glucose levels - glucose 5, 10 and 40%; insulin.
• Artificial ventilation lungs is used for extremely severe hypothermia, when the victim is unable to breathe on his own.
• An external cardioverter and defibrillator are used when serious heart rhythm disturbances occur. The cardioverter artificially causes contraction of the heart muscle when an excessively long pause occurs. A defibrillator is used when ventricular fibrillation and pulseless tachycardia occur.
• An electrocardiograph is used continuously to monitor cardiac activity.

When the patient's condition improves and the threat to life disappears, he is transferred to the general therapy department or any other department at the discretion of the attending physician for further recovery.

Prevention of hypothermia

Practical recommendations:

• Clothes should be warm and dry, preferably made from natural materials.
• Open parts of clothing must be tightened as tightly as possible to prevent air from entering under them.
• A hood is an extremely useful piece of clothing, as it significantly improves head protection from wind, rain and snow.
• It is necessary to find natural shelter from the wind, for example, cliffs, caves, walls of buildings and entrances. Good protection from the wind can be achieved by constructing a canopy of branches, or simply burying yourself in a pile of leaves or a haystack. In order not to suffocate, it is necessary to provide a small hole for ventilation.
• Shoes must match your foot size. The sole must be at least 1 cm thick.
• Active movements such as squats and running in place increase heat production and reduce the chances of hypothermia.
• If possible, it is necessary to drink hot drinks as often as possible.
• Alcohol is contraindicated for consumption in cold weather as it increases heat transfer.
• In cold weather it is necessary to provide a diet big amount fats and carbohydrates, as well as introduce additional meals into the daily routine.
• An external heat source, such as a fire, greatly increases your chances of avoiding hypothermia.
• If necessary, it is necessary to ask passers-by for help and stop passing cars.

Content.

Introduction.
Basic concepts.
Etiology of cooling.
Risk factors for cooling the body
Pathogenesis of hypothermia, stages.
Vicious circles.
Treatment of hypothermia and first aid for frostbite and freezing.
Principles of hypothermia prevention.
Medical hibernation.
Conclusion.
Bibliography.

Introduction.
Doctors often encounter hypothermic conditions and it is important to know what it is.
It is important to understand the concepts: hypothermic state, hypothermia itself, controlled hypothermia, frostbite. Then it is necessary to consider the causes, stages of development of the hypothermic state, treatment, prevention and finally application in medicine. Without knowledge of the pathophysiology of the hypothermic state, it is impossible in the future to fully competently treat and apply body cooling in the doctor’s practice.

Basic concepts.
Hypothermic conditions are characterized by a decrease in body temperature below normal. Their development is based on a disorder of the thermoregulation mechanisms that ensure the optimal thermal regime of the body. A distinction is made between cooling the body (hypothermia itself) and controlled (artificial) hypothermia, or medical hibernation.
Hypothermia - standard form disorders of heat metabolism - occurs as a result of the effect on the body of low ambient temperature and a significant decrease in heat production. Hypothermia is characterized by a disruption (failure) of thermoregulation mechanisms and is manifested by a decrease in body temperature below normal.
Under the influence of low temperatures, local cooling (frostbite) and general cooling (freezing) occur.
Frostbite - a pathological condition caused by the local effect of cold on any part of the body.
Freezing - general hypothermia - occurs when the body temperature drops below 34 °C, and in the rectum - below 35 °C.

Etiology of cooling.
Reasons for development body cooling is diverse:

Low temperature external environment- the most common cause of hypothermia. The development of hypothermia is possible not only at negative (below 0 °C), but also at positive external temperatures. It has been shown that a decrease in body temperature (in the rectum) to 25 °C is already life-threatening; up to 17-18 °C - usually fatal.
Extensive muscle paralysis or reduction in muscle mass (for example, with muscle wasting or dystrophy).
Metabolic disorders and decreased efficiency of exothermic metabolic processes. Such conditions can develop with adrenal insufficiency, leading to a deficiency of catecholamines in the body; in severe hypothyroid conditions; for injuries and dystrophic processes in the centers of the sympathetic nervous system.
Extreme degree of exhaustion of the body.

Risk factors cooling the body.

Increased air humidity.
High air speed (strong wind).
Increased humidity of clothes or their getting wet.
Exposure to cold water. Water has approximately 4 times more heat capacity and 25 times more thermal conductivity than air. In this regard, freezing in water can occur at relatively high temperature: at a water temperature of +15 °C a person remains viable for no more than 6 hours, at +1 °C - approximately 0.5 hours.
Prolonged fasting, physical fatigue, alcohol intoxication, as well as various diseases, injuries and extreme conditions.

In addition, risk factors for frostbite include:

tight shoes,
use of a tourniquet for blood loss.

Pathogenesis of hypothermia.
The development of hypothermia is a staged process. Its formation is based on more or less prolonged overexertion and, ultimately, a breakdown of the body’s thermoregulation mechanisms. In this regard, with hypothermia (as with hyperthermia), two stages of its development are distinguished: compensation (adaptation) and decompensation (maladaptation).
Compensation stage
The compensation stage is characterized by the activation of emergency adaptive reactions aimed at reducing heat transfer and increasing heat production.

Changing an individual’s behavior (directed leaving a cold room, using warm clothes, heaters, etc.).
Reduced heat transfer (achieved by reducing and stopping sweating, narrowing arterial vessels skin and subcutaneous tissues).
Activation of heat production (due to increased blood flow in internal organs and increased muscle contractile thermogenesis).
Turning on the stress response (excited state of the victim, increased electrical activity of thermoregulation centers, increased secretion of liberins in the neurons of the hypothalamus, in the adenocytes of the pituitary gland - ACTH and TSH, in the adrenal medulla - catecholamines, and in their cortex - corticosteroids, in the thyroid gland - thyroid hormones) .

Thanks to the complex of these changes, body temperature, although it decreases, does not yet go beyond the lower limit of normal. If causative factor continues to act, compensatory reactions may become insufficient. At the same time, the temperature of not only the integumentary tissues, but also the internal organs, including the brain, decreases. The latter leads to disorders of the central mechanisms of thermoregulation, incoordination and ineffectiveness of heat production processes - their decompensation develops.
Stage of decompensation
The stage of decompensation (disadaptation) is the result of a breakdown of the central mechanisms of thermoregulation. At the stage of decompensation, body temperature drops below normal levels (in the rectum it drops to 35 °C and below). The body's temperature homeostasis is disrupted: the body becomes poikilothermic. Often formed vicious circles, potentiating the development of hypothermia and disorders of the body’s vital functions.
The deepening of hypothermia causes inhibition of functions, first cortical, and subsequently subcortical nerve centers. Physical inactivity, apathy and drowsiness develop, which can result in coma. In this regard, the stage of hypothermic “sleep” or coma is often distinguished.
As the effect of the cooling factor increases, freezing and death of the body occurs.

Pathogenesis of frostbite.
Exposure to cold leads to prolonged spasm of peripheral vessels, disruption of microcirculation with the subsequent development of thrombosis and tissue necrosis. Changes in the affected areas are detected some time after cooling, therefore, during frostbite, 2 periods are distinguished: a pre-reactive (hidden) period, or a period of hypothermia, lasting until the start of warming and the appearance of signs of restoration of blood circulation (from several hours to 1 day), and a reactive period, which occurs after warming the affected area and restoring blood circulation.
In the latent period, pallor of the skin and loss of sensitivity in the area of ​​frostbite are noted. In the reactive period, depending on the depth of tissue damage, 4 degrees of frostbite are distinguished:
- I degree: purplish-bluish coloration of the skin, slight hyperemia and swelling appear.
- II degree: blisters filled with transparent exudate form on the skin.
- III degree: the affected areas of the skin are covered with blisters with hemorrhagic exudate, which indicates necrosis of the skin and subcutaneous tissue, involving blood vessels.
- IV degree: necrosis occurs not only of all layers of soft tissues, but also of the underlying bones, followed by mummification of damaged tissues, the formation of a demarcation line and the development of gangrene.
Frostbite I degree(the mildest) usually occurs with short exposure to cold. The affected area of ​​the skin is pale, turns red after warming, and in some cases has a purplish-red tint; edema develops. There is no dead skin. By the end of the week after frostbite, slight peeling of the skin is sometimes observed. Full recovery occurs 5-7 days after frostbite. The first signs of such frostbite are a burning sensation, tingling sensation followed by numbness of the affected area. Then skin itching and pain appear, which can be either minor or severe.
Frostbite II degree occurs with prolonged exposure to cold. In the initial period there is pallor, coldness, loss of sensitivity, but these phenomena are observed with all degrees of frostbite. Therefore, most characteristic feature- formation in the first days after injury of blisters filled with transparent contents. Complete restoration of the integrity of the skin occurs within 1 - 2 weeks, granulations and scars are not formed. In case of frostbite of the second degree after warming up, the pain is more intense and lasting than with frostbite of the first degree, skin itching and burning are disturbing.
At frostbite III degree the duration of the period of cold exposure and decrease in temperature in tissues increases. The blisters that form in the initial period are filled with bloody contents, their bottom is blue-purple, insensitive to irritation. The death of all skin elements occurs with the development of granulations and scars as a result of frostbite. Fallen nails do not grow back or grow deformed. The rejection of dead tissue ends in the 2nd - 3rd week, after which scarring occurs, which lasts up to 1 month. The intensity and duration of pain is more pronounced than with frostbite of the second degree.
Frostbite IV degree occurs with prolonged exposure to cold; the decrease in temperature in the tissues is greatest. It is often combined with frostbite of the third and even second degree. All layers of soft tissue die, bones and joints are often affected.
The damaged area of ​​the limb is sharply bluish, sometimes with a marbled coloration. Swelling develops immediately after warming and increases rapidly. The skin temperature is significantly lower than the tissue surrounding the frostbite area. Bubbles develop in less frostbitten areas where there is frostbite of the III-II degree. The absence of blisters with significantly developed edema and loss of sensitivity indicate degree IV frostbite.
Frostbite of the first degree is characterized by skin damage in the form of reversible circulatory disorders. The victim's skin is pale in color, somewhat swollen, its sensitivity is sharply reduced or completely absent. After warming, the skin becomes blue-purple in color, swelling increases, and dull pain is often observed. Inflammation (swelling, redness, pain) lasts for several days, then gradually goes away. Later, peeling and itching of the skin occurs. The frostbitten area often remains very sensitive to cold.
Frostbite of the second degree is manifested by necrosis of the superficial layers of the skin. When warmed up, the pale skin of the victim acquires a purplish-blue color, and tissue swelling quickly develops, spreading beyond the frostbite. In the frostbite zone, blisters filled with transparent or white liquid. Blood circulation in the area of ​​damage is restored slowly. Impairment of skin sensitivity may persist for a long time, but at the same time significant pain is noted.
This degree of frostbite is characterized by general symptoms: increased body temperature, chills, poor appetite and sleep. If a secondary infection does not occur, a gradual rejection of dead skin layers occurs in the damaged area without the development of granulation and scars (15-30 days). The skin in this area remains bluish for a long time, with reduced sensitivity.
With third degree frostbite, a violation of the blood supply (vascular thrombosis) leads to necrosis of all layers of skin and soft tissue to varying depths. The depth of damage is revealed gradually. In the first days, skin necrosis is observed: blisters appear filled with dark red and dark brown liquid. An inflammatory shaft (demarcation line) develops around the dead area. Damage to deep tissues is detected after 3-5 days in the form of developing wet gangrene. The tissues are completely insensitive, but patients suffer from excruciating pain.
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As a result of exposure to cold, the body temperature can drop, causing hypothermia. Most often, hypothermia occurs if frosty weather is accompanied by strong winds or high humidity. The situation can be aggravated by alcohol consumption and work disturbances. immune system or depressive states. Hypothermia is facilitated by the presence of tight clothing or shoes.

In what case is hypothermia considered mild, how to determine the symptoms, classification of types, what first aid for hypothermia includes - you will learn about this and much more in this article.

Types of hypothermia

There are 3 degrees of hypothermia, which differ:

• Mild degree. In this case, body temperature can drop to 32 degrees. The person is conscious, his blood pressure remains normal. The patient has pale skin and goose bumps. As a result of rhythmic contractions of muscle fibers, trembling appears, which increases heat production by 200%. Breathing quickens and becomes shallow, weakness and drowsiness appear.
• With an average degree hypothermia, the patient’s body temperature drops to 29 degrees. The pulse and heart rate slow and blood pressure drops. The skin becomes cold to the touch, pale with a bluish tint. Since severe numbness of the muscles occurs, the person stops trembling. At this stage, the feeling of freezing disappears. The patient tries to lie down and fall asleep (which is absolutely forbidden to do). The victim's eyes react to light, but at the same time he stops moving. He can only react to strong painful sensations.
• Severe degree Hypothermia occurs when body temperature drops to 27 degrees. In this case, all processes in the body are disrupted, and coma may occur. The person does not respond to light or pain, his heartbeat is slow, his heart rhythm is disturbed. His skin turns blue, and frostbite of the 3rd - 4th degree often appears. Periodically, severe hypothermia may cause convulsions. Without timely medical assistance, the victim dies.

Stages depending on manifestations

Table of correspondence between the stage of hypothermia and characteristic signs:

Stage	Characteristic signs	Etiology
Dynamic	· Pallor of the skin; · "Goose pimples"; · Lethargy and slow reaction to external stimuli; · Slow speech and clumsiness; · Drowsiness and apathy; · Increased heart rate and breathing.	When hypothermia occurs, spasm of peripheral vessels is detected. All heat generation mechanisms are activated. The sympathetic and autonomic nervous systems begin to work actively.
Stuporous	· The skin remains pale; · Limbs and protruding parts of the face acquire a bluish tint; · There is no muscle tremors, since the muscles stiffen to such an extent that it is impossible to straighten the limbs; · A person assumes a “boxer” pose; · A superficial coma develops, in which a person reacts only to strong painful stimuli; · The pupils react to light and are moderately dilated; · Heartbeat slows down; · Breathing becomes shallow; · Frostbite of 1st – 2nd degree may occur.	At this stage, peripheral blood circulation worsens, metabolic processes in the brain slow down. There is a partial disconnection of the activity of the subcortical zone and the cerebral cortex. The brain's breathing centers are depressed.
Convulsive	· The patient's skin becomes pale blue, in some cases it may acquire a purple tint; · Severe muscle stiffness occurs, the patient cannot move; · There is a deep coma, in which the pupils do not react to light or the reaction becomes very weak; The patient does not respond to stimuli (including severe pain), is in an unconscious state; · There is no rhythmic breathing; · Heart rate does not exceed 30 per minute; · Attacks of generalized convulsions appear, which are repeated every half hour; · Frostbite of 3 – 4 degrees appears; · If body temperature drops to 23 degrees, death occurs.	Compensatory mechanisms cease to operate. Blood circulation at this stage is disrupted, resulting in damage to body tissues. As a result of disturbances in metabolic processes in the brain, its areas stop interacting, and foci of convulsive activity arise. This degree of hypothermia is marked by the slow functioning of the heart, namely the conduction system. The brain centers of heartbeat and breathing are depressed. Tissue necrosis occurs.

Hypothermia in water

If a person enters water at a temperature less than 33 degrees, the process of cooling the body begins. The lower this indicator, the faster the process occurs. The thermal conductivity of water is 20 times stronger than that of air, so human life expectancy depends on the rate at which the body cools. At temperatures from 4 to 15, it can live up to 5 hours. If this indicator drops below 4 degrees, then death can occur within 2 hours.

At the first stage of hypothermia, when suddenly entering cold water, breathing is impaired and vasospasm may occur, causing the person to lose consciousness and drown. Cold shock occurs as a result of massive irritation of the skin's cold receptors.

At the second stage of hypothermia in water, complications arise in the form of impaired coordination of movements and respiratory function. The victim may also experience convulsions and frostbite.

In case of cold injuries, it is necessary to pull the person out of the water, if necessary, give him artificial respiration and indirect massage hearts. If he feels satisfactory, then first of all they get rid of his wet clothes and try to warm him up.

First aid for hypothermia

In case of hypothermia, proceed as follows:

• The person needs to be brought into a warm room, wet and frozen clothes taken off, and changed into dry clothes;
• If this is not possible, they try to hide the person with hypothermia as much as possible from the wind and cold. Rub the affected areas of the body with a dry hand or mitten. You can also use alcohol for these purposes. In no case should you rub the damaged areas with snow, as this can increase heat transfer, as a result of which the patient’s condition will worsen;

• If there is frostbite, the damaged limbs should be immersed in water at a temperature not exceeding 18 degrees. Gradually over the course of an hour the temperature is raised to 36 degrees. Immersion of hands or feet in hot water can cause irreversible processes in tissues and provoke the development of complications. This can also cause a sharp drop in blood pressure and heart rhythm disturbances, leading to the development of a state of shock;
• After the bath, the patient is dried with a towel. If there is no damage to the skin, carry out light massage, which allows you to increase blood circulation and improve metabolic processes. Movements should be light, otherwise heart rhythm disturbances may occur;
• The patient should be laid down and covered with a warm blanket. He is given a warm drink (broth, tea, milk). In no case should you use alcohol, as it can cause a worsening of the condition;
• In the severe stage of hypothermia, the patient must be moved very carefully so as not to cause him unnecessary suffering and not cause cardiac arrhythmias;
• In case of severe hypothermia, a person should be immediately taken to medical institution to provide medical assistance, since trying to help him on your own will not be successful.

Lecture No. 8 Pathology of thermoregulation. Fever

1. Typical forms of thermoregulation disorders. Hyperthermia: types, stages and mechanisms of development. Structural and functional disorders in the body.

2. Heat stroke. Sunstroke. Adaptive reactions of the body during hyperthermia.

3. Hypothermia: types, stages and mechanisms of development. Structural and functional disorders in the body. Adaptive reactions during hypothermia.

4. Fever. Causes of febrile reactions; infectious and non-infectious fevers. Pyrogenic substances.

5. Stages of fever. Forms of fever depending on the degree of temperature rise and types of temperature

curves. Clinical significance fever.

Body temperature is one of the important parameters of homeostasis.

Optimum body temperature - necessary condition effective metabolism, plasticity and renewal of structures, functioning of organs, tissues, physiological systems and the whole organism.

Body temperature equal to 36.6 is one of the most important constants of the human body, on the preservation of which the vital activity of many cells depends.

Body temperature equal to 36.6 is called normothermia.

The action of various factors can lead to a change in the body’s heat balance, which manifests itself either hyperthermic, or hypothermic conditions :

Low body temperature is called hypothermia, increased – hyperthermia. During hypothermia, heat production mechanisms are activated in the body, and during hyperthermia, heat transfer mechanisms are activated.

Hypothermia. Mechanisms of heat production	Hyperthermia.Mechanisms of heat transfer
are switched on during body hypothermia, which occurs when the ambient temperature drops below 15°C.	are turned on during body hyperthermia, which occurs when the ambient temperature rises above 18-22.
1. Increased catabolism in cells with the release of energy; the process is regulated by the hypothalamic-pituitary system. Main source glycogen - liver.	1. Convection - conduction of heat from heated areas of the body to colder ones.
2. Muscle tremors: while mechanical work does not take place, but heat is released.	2. Heat radiation (radiation).
3. Lipolysis - breakdown of fats in adipose tissue cells.	3. Sweating.
4. Redistribution of blood from the skin to the internal organs.	4. Redistribution of blood from internal organs to the surface of the body.
5. Depression of the respiratory center and decreased evaporation of fluid through the lungs.	5. Increased respiratory rate (RR) and water evaporation through the lungs.
6. Change in behavior in search of warmth.	6. Change in behavior in search of coolness.

Hyperthermia (overheating)

Hyperthermia, or overheating of the body,- a typical form of heat exchange disorder, as a result of high ambient temperature or disturbance of heat transfer from the body.

Etiology: work in hot shops, in protective suits, in conditions of high air temperature.

Pathogenesis and symptoms: overheating (hyperthermia) develops from heat retention in the body due to the difficulty of heat transfer to the environment and thermoregulation disorders.
Heat production predominates over heat transfer .

Into the compensation stage overheating, physiological mechanisms of heat transfer are activated: heat conduction, heat radiation and sweating, peripheral vessels dilate, respiratory rate, which leads to heat transfer.
In the stage of decompensation- body temperature rises, agitation, a feeling of anxiety, respiratory rate, heart rate (130-140 beats per minute), metabolism, nitrogen content in urine appear, convulsive twitching is noted.

Complications: Acute overheating causes heat stroke

Exposure to scorching sun rays directly on the head leads to sunstroke, which is similar in course to heatstroke.
Outcomes: Further overheating causes a decrease in vegetative functions, development comatose state, which can lead to death from respiratory arrest during inspiration and cardiac activity during systole.

Heat and sunstroke

Heatstroke - a form of hyperthermia characterized by rapid development of vital signs dangerous level body temperature, which is 42-43 °C.

It is a consequence of rapid exhaustion and failure of adaptive processes characteristic of the stage of compensation for hyperthermia. Those, heatstroke is hyperthermia with a short stage of compensation, quickly turning into a stage of decompensation.

Causes of maladjustment :

Effect of high intensity thermal factor;

Low efficiency of the body's adaptation mechanisms to elevated environmental temperatures. Characterized by central nervous system disorder, anxiety, feeling very hot, shortness of breath, palpitations, low blood pressure, sometimes vomiting, convulsions, confusion, loss of consciousness, increased body temperature to 42’-43’ and above.
Death of a person heatstroke is usually the result:

Heart failure;

Stopping breathing;

Acute progressive intoxication developing in connection with renal failure and metabolic disorders.

Sunstroke.

Cause: direct impact of solar energy on the body, mainly on the head. Along with others, the greatest pathogenic effect is exerted by radiation heat, which simultaneously warms both the superficial and deep tissues of the body. Besides, infrared radiation It also intensively warms up the brain tissue, in which the neurons of the thermoregulation center are located. In this regard, sunstroke develops rapidly and is fraught with death.

Pathogenesis sunstroke is a combination of the mechanisms of hyperthermia and sunstroke itself, which includes:

Arterial and venous hyperemia of the brain;

Increase in education cerebrospinal fluid and excessive filling of the pia mater with it, which causes swelling and compression of the brain substance. Wherein venous hyperemia leads to plasmorrhagia, edema, hypoxia and multiple diapedetic hemorrhages in the brain tissue, including in the region of the nuclei of the thermoregulation center, which leads to disruption of its function in regulating heat transfer and generally maintaining temperature homeostasis.

Adaptive reactions of the body during hyperthermia

· vasodilation;

· sweating.

1. convection - thermal conduction of heat from heated areas of the body to colder ones.

2. heat radiation (radiation).

3.sweating.

4.redistribution of blood from internal organs to the surface of the body.

5.increase in breathing rate and evaporation of water through the lungs.

6.change in behavior in search of coolness.

Hypothermia

Definition. Hypothermia is a violation of heat balance with a decrease in core body temperature below 35 ° C.

Causes: 1. Low temperature of the external environment (water, air, surrounding objects, etc.) is the most common cause of hypothermia. 2. In warm weather, after a person has been lying motionless for a very long time on a cool surface in wet clothes in windy weather. 3. Painful conditions with loss of consciousness and a significant decrease in heat production in the body (for example, trauma, hypoglycemia, convulsions, stroke, intoxication with drugs or alcohol). 4. Lately common cause cooling is the breakdown of the air conditioner at night. 5. ↓ Resistance of the body to cooling under the influence of physical fatigue, prolonged fasting, extreme exhaustion of the body./

Types of hypothermia:

-endogenous hypothermia(depending on internal factors) - prolonged immobility, endocrine diseases (hypothyroidism, adrenal insufficiency);

-exogenous hypothermia(depending on external factors) - cold season, inappropriate clothing, low physical activity, introduction of blockers.

Stages of hypothermia:

1. compensation- consists of increasing heat production (increased muscle activity,

intensification of metabolic processes) and a decrease in heat transfer (spasm of peripheral vessels,

decreased breathing, bradycardia);

2. relative compensation- characterized by “breakdown” and distortion of thermoregulatory

mechanisms (dilation of skin vessels, rapid breathing, tachycardia, etc.) - body temperature

decreases;

3. decompensation- blood pressure drops, breathing takes on the characteristics of periodic, sharply

the level of metabolic processes decreases.

//Pathogenesis. Hypothermia is characterized by a disruption (failure) of thermoregulation mechanisms and is manifested by a decrease in body temperature below normal. Heat production mechanisms turn out to be ineffective.

Hypothermia occurs when heat loss exceeds heat production. Hypothermia slows down all physiological functions, including cardiovascular and respiratory system, nerve conduction, mental activity, neuromuscular reaction time and metabolic rate. Thermoregulation ceases at body temperature approximately below 30°C; further heating is possible only from an external source. - Renal cellular dysfunction and decreased levels of antidiuretic hormone lead to the production of large volumes of unconcentrated urine ( cold diuresis ). - Diuresis plus fluid leakage into the interstitial space causes hypovolemia . The vasoconstriction that occurs during hypothermia may mask hypovolemia, which in this case may manifest as sudden shock or cardiac arrest during rewarming (warm collapse) when peripheral vessels dilate. Getting into cold water is accompanied by rapid cooling of the body, since water has approximately 4 times more heat capacity and 25 times more thermal conductivity than air. In this regard, freezing in water can be observed at relatively high temperatures: at a water temperature of +15°C, a person remains viable for no more than 6 hours, at +1°C - approximately 0.5 hours. Intense heat loss occurs mainly through convection and carrying out. - Immersion in cold water may cause diver's reflex» with vasoconstriction in the visceral muscles; blood is shunted to vital important bodies(e.g. heart, brain). The reflex is especially pronounced in young children and can have a protective effect. Additionally, complete immersion in near-freezing water may protect the brain from hypoxia, reducing metabolic demands. This phenomenon probably underlies the reasons for survival after prolonged cardiac arrest due to critical hypothermia. Extensive muscle paralysis and/or reduction in muscle mass (for example, with muscle wasting or dystrophy). This may be caused by injury or destruction spinal cord, damage to the nerve trunks innervating the striated muscles, as well as some other factors (for example, Ca2+ deficiency in the muscles, muscle relaxants). Such conditions most often develop with adrenal insufficiency, leading (among other changes) to a deficiency of catecholamines in the body, with severe hypothyroid conditions, with injuries and degenerative processes in the area of ​​the centers of the sympathetic nervous system of the hypothalamus. In the last three cases, hypothermia develops under conditions of low external temperature. //

Adaptive reactions of the body during hypothermia.

1. Initially, due to the action of cold, a) peripheral vessels narrow, and b) heat transfer decreases. c) Heat production increases. These processes maintain normal body temperature for some time, which is also facilitated by increased blood pressure and muscle tremors (increases heat generation in the muscles).

2. If the cold continues to act, then due to increased heat loss and increased oxygen demand, hypoxia occurs ( oxygen starvation) and inhibition of peripheral vascular activity. Heat transfer increases, body temperature decreases. Metabolism slows down, functions are inhibited, blood pressure decreases, heart and breathing rhythms slow down, a feeling of fatigue and drowsiness appears. Death occurs from respiratory paralysis at a body temperature of 23-24 °C.

Symptoms of hypothermia:

First - intense trembling, which stops when body temperature drops below 31°C, which contributes to an even more rapid decrease in body temperature.

Further progressive dysfunction of the central nervous system; people don't feel cold. Drowsiness and stupor are followed by dazedness, irritability, sometimes hallucinations and, ultimately, coma. The pupils stop responding to light. Breathing and heartbeats slow and eventually stop. First, sinus bradycardia and slow atrial fibrillation develop, the terminal rhythm is ventricular fibrillation and asystole.

That is, symptoms progress from trembling and drowsiness to stupor, coma and death. Course and outcomes. - Lethal Exodus. A decrease in body temperature (in the rectum) to 25°C is life-threatening, to 20°C is usually irreversible, to 17-18°C is usually fatal. Mortality statistics from cooling: Hypothermia and death of a person during cooling is observed at air temperatures from +10°C to 0°C in approximately 18%; from 0°C to -4°C in 31%; from -5°С to -12°С in 30%; from -13°C to -25°C in 17%; from -26°С to -43°С in 4%. Maximum indicator mortality during hypothermia it is in the air temperature range from +10 °С to - 12 °С.

- Favorable Exodus.

There are cases where patients, after immersion in ice water for an hour or more (rarely) were successfully rewarmed without residual effects of brain damage, even when internal temperature body temperature was 13.7 °C and there was no reaction of the pupils to light. With the same degree and duration of hypothermia, recovery is more likely in children than in adults.

Fever

Definition: Fever – is a protective-adaptive reaction of the body to irritants of infectious and non-infectious nature, characterized by an increase in body temperature above normal, regardless on the ambient temperature.

Causes of fever: Fever is caused by the appearance of pyrogenic substances in the body.

There are fevers:

1. infectious (viruses, microorganisms);

2.non-infectious:

Exogenous (administration of vaccines, poisons);

Endogenous (formation in the body of substances as a result of disease, breakdown products of damaged

cells, altered serum proteins, etc.).

Three stages of fever:

Stage 1. - Temperature rise

Within a few hours, less often - within 2-3 days T.

Metabolism and heat production are enhanced,

A spasm of skin vessels occurs, which ↓ heat transfer. Heat accumulates and the body warms up. Vascular spasm causes a feeling of coldness and chills. How stronger spasm, the stronger the chill and the temperature rises faster;

Stage 2. - Relative temperature

Increased heat production and heat transfer.

Metabolism is significantly increased.

The breakdown of proteins is greatly increased, due to which the excretion of protein breakdown products in the urine is increased.

The patient is losing weight. Water and salts are retained in the body.

Urination is reduced, urine is dark, high density, concentrated;

Stage 3 - Temperature drop

Heat dissipation is enhanced.

The skin vessels are dilated, and the patient feels hot. Patients complain of high fever even when the temperature is normal or below normal. This is due to the fact that the impulses that give the sensation of heat arise as a result of vasodilation.

Distinguish a crisis (sharp drop in temperature and blood pressure), which has an unfavorable prognosis, and lysis , in which there is a gradual drop in body temperature and blood pressure, the prognosis is favorable.

When you have a fever, your metabolism changes. Due to the increasing demand for oxygen, breathing increases. For fever - tachycardia. When body temperature rises by 1 degree, the heartbeat increases by 10 beats. For fever blood pressure changes: First it increases and then decreases. From the side of the central nervous system General excitation occurs, and then inhibition of the nervous system occurs. Changed function of the digestive apparatus. Salivation decreases, which causes dry mouth and plaque on the tongue. The secretion of gastric juice and digestive gland juice decreases. Intestinal motility is impaired A. As a result, appetite disappears, digestion and absorption are disrupted. nutrients, diarrhea or constipation occurs. Dystrophic changes develop in many organs.

Forms of fevers depending on the degree of temperature rise:

· low-grade fever or weak: 37.1 - 38.0 °C;

· febrile fever or moderate: 38.1 - 39.0 °C;

· pyretic fever or high: 39.1 - 41.0 °C;

· hyperpyretic fever or very high: over 41.0 °C.

Types of temperature curves determined by the degree of daily temperature fluctuations. Has diagnostic value. Depends on the body's resistance.

1. Persistent fever(febris continua) - a long-term stable increase in body temperature, daily fluctuations do not exceed 1 °C (observed when lobar pneumonia, flu);

2. Relieving fever(febris remittens) - significant daily fluctuations in body temperature within 1-2 °C. But at the same time, the temperature does not drop to normal levels (observed with severe sore throat);

3. Intermittent fever(febris intermittis) - characterized by a rapid, significant increase in temperature, which lasts for several hours, and then is replaced by a rapid drop to normal values(observed in malaria);

4. Hectic, or debilitating fever(febris hectica) - daily fluctuations reach 3-5 °C, while temperature rises with a rapid decline can be repeated several times during the day (observed in sepsis);

5. Perverted Fever(febris inversa) - it is characterized by a change in the circadian rhythm with higher temperature rises in the morning;

6. Wrong fever(febris athypica) - which is characterized by temperature fluctuations throughout the day without a specific pattern;

7. Relapsing fever(febris recurrens) - characterized by alternating periods of increased temperature with periods of normal temperature, which last for several days.

Meaning of fever.

Considering that in evolution fever was formed as a typical, stereotypical reaction, in each person it is accompanied by both adaptive(mainly) and, under certain conditions, pathogenic effects.

The main adaptive effects of fever:

bacteriostatic and bactericidal effects;

Strengthening the mechanisms of the immunobiological surveillance system;

Activation of a nonspecific stress response as a component of the general adaptation process. At high temperatures, the production of antibodies accelerates, phagocytosis proceeds better, hematopoiesis increases, and the barrier and antitoxic functions of the liver increase. All this allows us to regard fever as adaptive reaction of the body.

/Most significant pathogenic effects fever:

1. Damaging effect on the body of high (especially excessive) temperature .

2. Pathogenic effects of the causes causing the development of fever(microbial endo- and exotoxins); foreign proteins and other compounds that can cause immunopathological processes (allergies, immunodeficiency, immune autoaggression diseases), etc.

3.Functional overload of organs and physiological systems, directly involved in the mechanism of development of fever (cardiovascular, respiratory, liver, etc.). For example, with a significant increase in body temperature, as well as with its critical drop, collapse, fainting or heart failure may develop.

4. Disorder of the functions of organs and systems not directly involved in the implementation of the febrile reaction, for example, the digestive system, which is characterized by decreased appetite, indigestion, and weight loss of the patient; nervous system, accompanied by headache, sometimes convulsions and hallucinations, impaired reflexes, etc./

Stage 1 - compensation.

Body temperature is maintained at a normal level, although the ambient temperature is low, which is achieved by limiting heat transfer, activating the sympathetic-adrenal system, causing spasm of skin microvessels, thereby limiting heat transfer. At the same time, there is an increase in heat production due to increased motor activity, contraction of smooth muscles of the skin (“goose bumps”), and an increase in oxidative processes in tissues.

Stage 2 - relative compensation.

Develops at very low ambient temperatures or disruption of the thermoregulation system. At this stage of the development of hypothermia, there is a combination of thermoregulation disorders and protective-adaptive reactions (increased oxidative processes in tissues). Heat transfer prevails over heat production, which causes a decrease in body temperature.

Stage 3 - decompensation.

Hypoxia develops due to weakening of external respiration, depression of cardiac activity, microcirculation disorders, and a decrease in oxidative processes in tissues. The patient becomes indifferent to the environment, immobilized, there is a strong physical weakness, bradycardia and drop in blood pressure, rare shallow breathing. A person develops deep dream. If he is not helped, he will die. Hypothermia reduces the body's need for oxygen and increases resistance to pathogenic influences, which are used during severe surgical operations (general and local hypothermia or “artificial hibernation”).

Fever.

Fever - general reaction body for damage the most important feature which is an increase in temperature. This is a typical pathological process that occurs under the action of a pyrogenic agent, which is based on an active restructuring of the functions of the thermoregulation center. Fever is one of the common manifestations of diseases; sometimes it can be the first and only symptom of the disease for a long time.

Etiology of fever:

Fever is polyetilogical. Based on etiology, fever is divided into non-infectious and infectious. There are a large number of non-communicable diseases accompanied by the development of fever. These include cerebral hemorrhages, traumatic tissue damage, burns, myocardial and other organ infarctions, allergic diseases, etc. To infectious factors include pathogenic viruses, microbes, fungi, and protozoa. Their components, waste products, are called pyrogenic substances (from the Greek Pyros - fire, pyr - heat), which are divided into exogenous and endogenous.

Exogenous pyrogens isolated from microbial cells, they are integral part endotoxins. Some microbial exotoxins, such as diphtheria toxin and hemolytic streptococcus toxin, also have pyrogenic properties. The action of exogenous pyrogenic substances is mediated through endogenous pyrogens, which are pilipeptides or proteins. The place of formation of endogenous pyrogens is all phagocytic cells (neutrophils, monocytes, macrophages, RES cells of the liver and spleen).