Hypothermia

Hypothermia - decrease in internal body temperature below 35 ° С. Symptoms progress from trembling and drowsiness to stunning, coma and death.

With moderate hypothermia, it is sufficient to be in a warm environment and warming with blankets (passive warming). Severe hypothermia requires active warming of the body surface (in particular, with systems with a warm air flow, radiant heaters, electric heaters) or the internal environment of the body (for example, lavage of the body cavities, extracorporeal warming of the blood).

Hypothermia develops when heat loss exceeds its production. Hypothermia is most common in the cold season or when immersed in cold water, but it is also possible in warm weather, after a very long stationary lying of a person on a cool surface (for example, in a state of intoxication) or after a very long time in water with a temperature, for swimming (for example, 20-24 ° C).

From primary hypothermia, about 600 people die each year in the United States. Hypothermia also has a significant and not always understandable effect on the risk of death in cardiovascular and neurological diseases.

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Causes of hypothermia

Immobility, wet clothes, windy weather and lying on a cold surface increase the risk of hypothermia. Conditions that cause loss of consciousness, immobility or all together (for example, trauma, hypoglycemia, seizures, stroke, intoxication with drugs or alcohol) are the most characteristic predisposing factors.

Hypothermia slows down all physiological functions, including the functions of the cardiovascular and respiratory system, nerve conduction, mental activity, the time of neuromuscular reactions and the level of metabolism. Thermoregulation ceases at body temperature below about 30 ° C; further warming is possible only from an external source. Renal cell dysfunction and a decrease in the levels of antidiuretic hormone lead to the production of a large volume of unconcentrated urine (cold diuresis). Diuresis plus fluid leakage into the interstitial space causes hypovolemia. Vasoconstriction that occurs with hypothermia can mask hypovolemia, which in this case can manifest as sudden shock or cardiac arrest during warming (collapse when warming), when peripheral vessels dilate.

Immersion in cold water can cause a reflex of the "diver", with vasoconstriction in the visceral muscles; the blood is shunted to vital organs (for example, the heart, the brain). The reflex is especially pronounced in young children and can have a protective effect. In addition, a full immersion in water with a temperature close to freezing can protect the brain from hypoxia, reducing metabolic needs. This phenomenon probably underlies the causes of cases of survival after prolonged cardiac arrest due to critical hypothermia.

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Symptoms of hypothermia

First, an intense tremor occurs, but it stops when the body temperature drops below 31 ° C, which contributes to an even faster decrease in body temperature. With a decrease in body temperature, dysfunction of the central nervous system progresses; people do not feel cold. Behind drowsiness and numbness are followed by stunnedness, irritability, sometimes hallucinations and, ultimately, coma. Pupils do not react to light. Breathing and heartbeat slow down and eventually stop. First develop sinus bradycardia and slow atrial fibrillation, terminal rhythm - ventricular fibrillation and asystole. However, such rhythm disturbances are potentially not as dangerous as in normothermia.

Diagnosis of hypothermia

The diagnosis is made according to rectal thermometry. Electronic thermometers are more preferable, as for standard mercury thermometers the lower limit of measurement is 34 ° C, even for special low-temperature ones. Esophageal sensors and thermistor sensors for pulmonary artery catheters provide the most accurate information, but are not always available.

It is necessary to identify the reasons. Laboratory tests include a general blood test, determination of plasma glucose concentrations, electrolytes, urea nitrogen, creatinine, and blood gas composition. The gas composition of blood at a low temperature does not correct. The ECG is characterized by the appearance of the tooth J (tooth Osborne), and lengthening the intervals PR, QT, set the QRS, although this is not always the case. If the cause of hypothermia is unclear, determine the content of alcohol and drugs in the blood, test the function of the thyroid gland. You should think about sepsis, a latent skeletal or craniocerebral trauma.

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Prognosis and treatment of hypothermia

Patients after immersion in ice water for an hour or more (rarely) were successfully warmed up without residual brain damage (see the corresponding section), even when their internal body temperature was 13.7 ° C and the pupils' reaction to light was absent. It is difficult to predict the outcome, and it can not be determined on the basis of the Glasgow coma scale. A sign of cell lysis (hyperkalemia> 10 mEq / L) and intravascular thrombosis (fibrinogen <50 mg / dL) can be classified as serious prognostic markers. With the same degree and duration of hypothermia, recovery in children is more likely than in adults.

First of all, it is necessary to stop further loss of heat, remove wet clothes, wrap the patient in blankets, insulate the head. Follow-up depends on the severity of hypothermia, the presence of unstable hemodynamics, or cardiac arrest. Return of the patient to normal body temperature after hypothermia does not require such urgency, as after severe hyperthermia. For stable patients it is acceptable to increase the internal temperature of the body by 1 ° C / h.

If the hypothermia is moderate and the thermoregulation is not disturbed (this is indicated by a shiver and body temperature in the range of 31 -35 ° C), warming with blankets and hot drinking is sufficient.

Recovery of fluid volume with hypovolemia is very important. Patients are given 1-2 l of 0.9% sodium chloride solution intravenously (20 ml / kg body weight for children); heated, if possible, to 45 ° C. A larger amount may be needed to maintain a normal level of blood supply to organs.

Active warming is required if patients have hemodynamic instability, body temperature <32,2 ° С, endocrine insufficiency or hypothermia, which has developed again after trauma, poisoning or disease. If the body temperature is closer to the upper limit of the critical range, heating can be heated using hot water or hot air blowing. Patients with lower temperatures, especially those with low blood pressure or cardiac arrest, need internal warming. The method of choice is lavage of the abdominal and thoracic cavities with a hot 0.9% solution of sodium chloride. Warming blood in an arteriovenous or venovenous contour (as in hemodialysis) is more effective, but much harder to perform. The most effective device of artificial circulation. These extracorporeal measures require a pre-prepared treatment protocol and trained medical personnel.

Cardiopulmonary resuscitation is not performed in the presence of a heart rhythm sufficient for blood supply to organs, even in the absence of a pulse; liquid administration and warming are continued as described above. Arterial hypertension and bradycardia with low internal body temperature are expected, and with isolated hypothermia, aggressive treatment is not required. Patients with ventricular fibrillation or asystole begin cardiopulmonary resuscitation, closed cardiac massage and intubation of the trachea. At a low body temperature, defibrillation is difficult. If the 1st or 2nd attempts are ineffective, defibrillation should be postponed until the temperature limits rise> 28 ° C. Intensive therapy is continued until the body temperature reaches 32 ° C, in the absence of injuries or diseases incompatible with life. However, cardiotropic drugs (such as antiarrhythmics, vasopressors, inotropes) are usually not used. Small doses of dopamine (1-5 μg / kg hmin) or infusion of other catecholamines are administered to patients with disproportionately severe arterial hypotension or not responding to the introduction of crystalloids and warming. Severe hyperkalemia (> 10 mEq / L) during resuscitation usually indicates a fatal outcome and may serve as one of the criteria for stopping resuscitation.