Hypothermia is a decrease in the internal temperature of the body to 35 ° C and below as a result of the predominance of heat transfer over heat production. At the initial stage, there is trembling, increased breathing and palpitations, spasm of peripheral vessels, disorientation, drowsiness, apathy. Subsequently, the suppression of the activity of all organs and systems is noted, with the aggravation of the condition, coma and death occur. Hypothermia is diagnosed on the basis of clinical data, the results of measuring the base temperature, instrumental and laboratory tests are prescribed as additional methods. Treatment includes active and passive warming, drug therapy, resuscitation measures.
Hypothermia is a pathological condition that can pose a danger to the patient’s life. According to statistics, approximately 700 people die annually in the USA due to hypothermia, 300 in the UK, and 100 in Canada. Experts believe that the real number of deaths from hypothermia is higher, since this condition is not always diagnosed. Pathology is widespread everywhere, more common in northern and temperate latitudes, the number of cases increases in the cold season. The risk of developing hypothermia increases in representatives of extreme age groups – infants and young children, the elderly and the elderly. In sparsely populated areas, hypothermia usually occurs due to insufficient preparedness to stay in existing weather conditions. In cities, homeless people and people who are intoxicated after drinking alcohol are more likely to become victims of hypothermia.
Hypothermia develops due to increased heat loss, which cannot be compensated due to increased heat production by the body. Heat loss occurs as a result of conduction, convection and evaporation. Conduction is the direct transfer of heat from the body to the environment, convection is the loss of heat when water or air moves in close proximity to the surface of the body, evaporation is the release of heat with water during sweating, breathing. There are four main causes of hypothermia:
- Lack of heat production. It is observed in premature infants, elderly people, patients with alimentary dystrophy, exhaustion against the background of severe injuries, acute and chronic diseases. It is found in some hormonal disorders – hypocorticism, hypopituitarism and hypofunction of the thyroid gland.
- Increased heat loss. It is noted with vasodilation due to intoxication (most often alcohol), taking medications. Develops with prolonged stay in dry cold, immersion in cold or cool water. It is determined in some skin pathologies, for example, ichthyosis, psoriasis and exfoliative dermatitis. Sometimes it becomes the result of medical actions (during prolonged surgical interventions, massive transfusion of cold solutions).
- Violations of thermal regulation. They are detected in some diseases and traumatic injuries of the central and peripheral nervous system, accompanied by sensory disorders (for example, damage to large nerve trunks, paralysis on the background of stroke, traumatic brain or spinal injury, especially high, multiple sclerosis, central nervous system tumors, Parkinson’s disease). They may occur under the influence of certain toxins and medications.
- Within the framework of critical conditions. It can be determined with polytrauma, massive blood loss of various genesis, acute pancreatitis, septic conditions, extensive burns, uremia, diabetic ketoacidosis. It is provoked by thermoregulation disorders, increased percutaneous water loss, behavioral disorders and other causes.
- Pathology often has a polyethological origin. For example, in elderly and bedridden patients with insufficient care, age-related or heat regulation-related lack of heat production, low room temperature, chronic diseases are important. The most significant external factors are ambient temperature, humidity and wind strength. When staying in the air without movement at zero temperature, death occurs within 10-12 hours, under similar conditions in water – after half an hour.
The influence of wind is calculated on the basis of the wind-cold index, there are special tables compiled with this indicator in mind, reflecting the danger of hypothermia or frostbite under certain weather conditions. Despite the increase in the risk of hypothermia as the temperature decreases, the largest number of cases of the disease in healthy people, according to the observations of traumatologists, is associated with being outdoors in conditions of low positive, not negative temperatures, which may be explained by insufficient alertness, unpreparedness for environmental conditions.
Hypothermia is a two-stage process, including a compensation stage that occurs when the body tries to correct a violation of the thermal balance, and a decompensation stage that develops when the mechanisms of temperature regulation are disrupted. In the compensation stage, the body’s reactions are activated, aimed at reducing heat loss and increasing heat production. The patient changes behavior (finds shelter, puts on warm clothes, turns on the heater, uses blankets, etc.). Due to the narrowing of peripheral vessels and reduced sweating, heat loss through the skin decreases. The blood flow in the internal organs increases, involuntary muscle contractions (muscle trembling) occur, providing an increase in heat production. Diuresis increases. There is a release of hormones that are involved in stress reactions that increase the body’s defenses in extreme circumstances.
With the inefficiency of adaptive mechanisms and a further decrease in body temperature, the central mechanisms of heat regulation are disrupted, heat production becomes uncoordinated and ineffective. The central temperature drops below 35 ° C, poikilothermic reactions occur, vicious circles form, aggravating the patient’s condition. Due to the decrease in temperature, the intensity of tissue metabolism decreases, which leads to a further decrease in temperature and a decrease in metabolism. The narrowing of peripheral vessels is replaced by their expansion, which entails an increase in heat loss, which provoke further dilation of the vessels.
Due to a violation of the activity of nerve centers, muscle trembling stops, which potentiates a drop in body temperature and further inhibition of the central mechanisms of regulation of muscle activity. Hypothermia of the central nervous system is the cause of a decrease in brain activity, as a result, disorders of consciousness, drowsiness, apathy develop. Active actions become impossible, the patient freezes, which reduces the chances of salvation. There comes a state of apparent peace, pseudo-discomfort, which subsequently goes into a coma and ends with the death of the patient.
There are several classifications of hypothermia. Since the severity of the manifestations does not always coincide with the severity of hypothermia, to assess the reversibility of the process, hypothermia is sometimes systematized taking into account the central body temperature. According to this division, there are four stages of pathology: three reversible (mild – 32-33 ° C, moderate – 28-32 ° C, severe – 24-28 ° C) and one irreversible (extremely severe – less than 24 ° C). However, in clinical practice, a classification is more often used, compiled on the basis of prevailing compensatory reactions and including three degrees of hypothermia:
- Light or adynamic (32-34°C). It is accompanied by activation of heat generation mechanisms, narrowing of peripheral vessels, stress stimulation of the sympathetic nervous system.
- Medium or soporose (29-32°C). It is manifested by depletion of compensatory mechanisms, slowing of metabolism in the central nervous system, discoordination of the cortical and subcortical nerve centers, depression of the respiratory and cardiac centers in the medulla oblongata, significant deterioration or cessation of blood flow in peripheral vessels, possibly frostbite.
- Severe or comatose (below 31°C). It is characterized by disruption of compensation mechanisms, severe metabolic disorders and serious disorders of brain structures, disorders of the cardiac conduction system, damage to peripheral tissues up to icing.
With a mild degree, chills, muscle tremors occur, the skin becomes pale, acquires a bluish hue. Goose bumps and typical speech disorders are detected. Mild bradycardia is noted. Blood pressure is usually unchanged or slightly elevated, breathing is rapid. At first, the patient actively moves, takes measures to save. With the continuation of the cold, the patient becomes sluggish, apathetic. Speech, thought processes and reactions to external influences slow down. In some patients, superficial frostbite is detected.
With an average degree, further aggravation of bradycardia, a slight decrease in blood pressure and a decrease in breathing to 8-12 respiratory movements per minute are determined. Cyanosis of the skin increases, becomes especially pronounced in the nose, ears, distal extremities, the likelihood of frostbite increases. The amount of urine excreted decreases due to a decrease in renal blood flow. The muscle trembling stops, the muscles stiffen, the patient takes a forced pose – rounds his back, bends his arms and legs, brings them to the trunk. Pronounced drowsiness turns into hypothermic sleep and then into a coma, the reaction to external stimuli is significantly weakened, often detected only with painful effects. Pupils dilated, react to light.
The diagnosis is established on the basis of an external examination, anamnesis data (in case of severe hypothermia, the data are established from the words of eyewitnesses who found the victim, or ambulance staff) and the results of body temperature measurement. The measurement in the armpit reflects the surface temperature and is not a reliable criterion for the presence or absence of hypothermia. The measurement is carried out rectally, using an esophageal probe or in the nasopharynx, given that the rectal temperature may differ slightly from the baseline, and the readings taken in the esophagus may be unreliable due to previous therapy with warm air.
In modern clinical practice, special electronic thermometers equipped with a probe are used, calibrated in the range of low temperatures. It is possible to measure the temperature of a fresh portion of urine. The best option is to carry out several measurements in different places. It should be borne in mind that the drop in the base temperature below the critical indicators, the absence of heartbeat and respiration cannot be considered as evidence of the death of the patient (a case of survival at a temperature of 9 ° C is described, as well as recovery after cessation of cardiac activity for 3 hours) due to the action of hypothermia, slowing the development of irreversible processes in tissues. Death is pronounced only in the absence of signs of life after warming up.
To confirm the diagnosis, along with temperature measurement, an ECG is prescribed, on which the Osborn wave is detected. The list of other laboratory and instrumental studies in case of suspicion of this pathology includes blood test, urinalysis, determination of urea, creatinine, glucose, electrolytes, acid-base state and blood pH, coagulogram, measurement of blood pressure and hourly diuresis, pulse oximetry, chest x-ray. In case of injuries of the musculoskeletal system, radiography of the corresponding segment is performed, ultrasound, CT or MRI is prescribed for possible damage to internal organs, laparoscopy and other studies are performed according to indications.
Treatment is carried out by specialists in the field of practical traumatology and resuscitation. Therapeutic tactics are determined by the degree of hypothermia, the nature and severity of disorders of the vital activity of the body. In all cases, it is urgently necessary to stop the effects of cold, to carry out measures for passive warming. Patients with a mild degree are prescribed a warm drink (sweet tea), a warm bath, hot water bottles, avoiding the use of excessively heated liquids. With superficial frostbite, warming bandages are applied to the limbs.
In moderate and severe cases, intensive complex therapy is necessary, including etiotropic, pathogenetic and symptomatic measures. Etiotropic treatment involves passive (blankets, warm dry clothes) and active (warm bath, applying hot water bottles to the places of passage of large vessels) warming. Active warming is carried out using a liquid whose temperature exceeds the temperature of the victim by no more than 10 ° C. After the rectal temperature rises to 33-34 ° C, the procedure is stopped in order to avoid possible overheating against the background of the heat regulation system that has not yet recovered.
Along with the above methods, it is effective to warm the lungs by supplying moist air or an oxygen mixture heated to 42-44 ° C, intravenous infusions of warm solutions. With resistance to the above methods, mediastinal lavage, extracorporeal blood warming (hemodialysis, cardiopulmonary, veno-venous and arteriovenous bypass surgery), gastric lavage, bladder, rectum, pleural cavity with warm solutions are performed, however, these techniques are associated with the risk of complications, therefore they are not used as part of standard therapy.
Pathogenetic treatment is based on measures to restore the activity of the respiratory and cardiovascular systems, correction of metabolic disorders. The respiratory tract is released, a ventilator is performed. If necessary, defibrillation is performed. Perform infusion infusions of dextran, saline solutions, glucose solution with vitamins and insulin, according to indications – transfusions of plasma and plasma substitutes. As part of symptomatic therapy, drugs are prescribed to normalize urination, increase blood pressure, eliminate pain, prevent pulmonary and brain edema, and correct existing somatic pathology. When determining the plan for drug correction of the patient’s condition, it is taken into account that medicines in conditions of severe hypothermia may be ineffective or have an unpredictable effect and should be used after sufficient warming. The treatment of frostbite is carried out.
Prognosis and prevention
The prognosis usually (with the exception of particularly severe cases) depends more on the concomitant pathology than on the severity of hypothermia. Mortality among healthy people is low. In the presence of severe injuries and somatic diseases, mortality rates increase dramatically. A characteristic feature of this condition is the possibility of recovery after a prolonged cessation of the activity of vital organs, due to the protective effect of cooling. Preventive measures include the choice of clothing and planning activities outside of warm shelters, taking into account weather conditions, correction of pathological conditions that are risk factors, ensuring optimal temperature conditions in the premises, especially when people with a predisposition to hypothermia live in them.
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