General cooling of the body - freezing - is a violation of the thermal balance in the body itself, leading to a decrease in body temperature. Usually, when there is a threat of a decrease in body temperature, the body regulatoryly strives to produce heat, which is facilitated, for example, by muscle tremors. For this reason, being in the cold for a long time, a person at a certain moment, feeling the cold creeping through him, begins to shake, chatter his teeth, and shudder. As a rule, a person does not test the limits of adaptive reactions and tends to wrap himself in clothes at the first signs of cooling, rather to get into the warmth; if he is wet, take off wet clothes, etc. If such behavior is impossible for some reason (the person does not realize the danger situations, for example, in a state of alcoholic or drug intoxication, he is prevented from doing this by any metabolic, hormonal or neurological disorders, an accident on the water, for example, a fall through the ice, an avalanche, or a person simply homeless), then further cooling is fraught with the development hypothermia - a decrease in the temperature of the “core” of the body to 35 ℃ and below. Being in 5–10 degree water (on New Year’s Eve and not only, alas, people often find themselves in bodies of water in inappropriate weather) can lead to hypothermia within 10 minutes. And being in wet clothes at 0 ℃ and strong winds in less than an hour can result in irreversible hypothermia.
Pathogenetically, the process of freezing and the onset of hypothermia can be divided into 3 stages.
Causes
Hypothermia is a decrease in core body temperature below 35°C.
The most common causes of hypothermia are: prolonged general or regional anesthesia, exposure to cold (especially while intoxicated), immersion in cold water, massive transfusions of cold solutions or blood products. And many other conditions that cause loss of consciousness and (or) immobility of the patient. For example: trauma, hypoglycemia, convulsions, stroke, poisoning, etc. The diagnosis of hypothermia rarely appears in medical histories. But this does not reflect the true state of affairs, but rather speaks of poor diagnosis of this condition in our clinics.
The temperature of the human body is not the same in different places, and internal readings are usually higher than those obtained closer to the skin. In some cases, the temperature of the “shell”, which includes the skin, subcutaneous tissue and muscles, may differ from the temperature of the core by tens of degrees. In our country, it is customary to measure temperature exclusively in the axillary region. Even under normal conditions, the temperature measured in the axillary (axillary) region is 1-2 degrees lower than the central one. Under conditions of hypothermia, the gradient increases in an unpredictable manner.
Axillary temperature measurements should not be used to determine the severity of hypothermia. To reliably judge the degree of hypothermia, temperature must be measured at one of the following points: rectum, bladder, nasopharyngeal region, esophagus, external auditory canal region. Mercury thermometers are structurally unsuitable for these purposes; moreover, their lower measurement limit is limited to 34°C. For hypothermia, electronic thermometers and special probes and sensors for them should be used.
Prevention
Prevention of hypothermia includes measures aimed at preventing hypothermia:
- organization of the correct work and rest regime in the winter season for people working outdoors;
- use of warm clothing and dry shoes suitable for weather conditions;
- medical control over the condition of participants in winter sports competitions, exercises, and military operations;
- organization of public heating points during frosts;
- avoiding drinking alcohol before being in the cold;
- hardening procedures that improve adaptability to changing climatic conditions.
Laboratory research
- General blood analysis;
- Blood electrolytes (sodium, potassium, magnesium, chlorides);
- Blood glucose;
- Urea, creatinine;
- Blood gases, pH, acid-base status;
- Blood lactate;
- Coagulogram;
- General urine analysis.
- Electrocardiogram (ECG);
- Chest X-ray;
- X-ray or CT scan of any part of the body if damage is suspected.
- Monitoring
- Pulse oximetry;
- ECG;
- Body temperature;
- Non-invasive blood pressure;
- Hourly diuresis.
Classification of hypothermia
There are many classifications, but most often hypothermia is divided into mild (32.2°C-35°C), moderate (27°C-32.2°C) and severe (<27°C). But from a practical point of view, it is advisable to classify its severity according to the patient’s ability to maintain (moderate hypothermia) or lose (severe hypothermia) the ability to independently (passively) warm. Since it is precisely this circumstance that has the greatest influence on the choice of therapeutic measures.
Moderate hypothermia (32°C-35°C)
Patients are disoriented, drowsy, apathetic, the degree of depression of consciousness varies, more often - stunning, tremors, tachycardia, tachypnea are characteristic. Vasoconstriction is observed. Blood glucose levels are elevated. With moderate hypothermia, the patient is able to warm himself. If the patient's consciousness is preserved, it is enough to place the patient in a warm room and well insulate his body (dry warm clothes, warm bed linen). Drinking a hot drink and covering your head with a blanket significantly speeds up the warming process.
Attention. ECG monitoring must be provided. Even with moderate hypothermia, the frequency of various cardiac arrhythmias increases significantly.
Severe hypothermia (<32°C)
Severe hypothermia causes dysfunction of many systems. The functions of the cardiovascular and respiratory systems, nerve conduction, mental activity, neuromuscular reaction time and metabolic rate are inhibited.
Attention. In severe hypothermia, the thermoregulation center stops working and the patient cannot warm up on his own. Active warming of the patient is necessary.
There is a progressive decrease in the level of consciousness. Delirium sometimes develops. There is no clear correlation between body temperature and the depth of coma on the Glasgow scale. But with a core temperature of <27°C, all patients develop coma, areflexia, and loss of pupillary response to light. A decrease in the level of antidiuretic hormone leads to polyuria (cold diuresis) and increases hypovolemia.
Trembling stops, heat production sharply decreases and basal metabolism decreases. There is a temperature-dependent decrease in blood pressure, heart rate, and respiratory rate to 8-10 per minute. The electrocardiogram records:
- sinus bradycardia,
- prolongation of the PQ interval,
- prolongation of the QRS complex,
- prolongation of the QT interval,
- T wave inversion
- appearance of a U wave.
Atrial fibrillation, atrioventricular nodal ventricular tachycardia[/anchor] may develop. Upward displacement of the ST segment indicates the danger of cardiac fibrillation. Most patients have early ventricular repolarization syndrome, characterized by the presence of ST segment elevation, j-spot, notch, or junction wave on the descending portion of the R wave.
The main criterion for the syndrome is the J-wave, which has different names: “Osborne wave”, “hypothermic wave”, etc. Initially, the J-wave becomes noticeable in the lower limb leads (II, III and aVF) and left thoracic (V5, V6) . As the central temperature decreases, its amplitude increases.
Signs of hypothermia
Symptoms of hypothermia are difficult to confuse with another diagnosis. In the initial stages, hypothermia is characterized by:
- redness of the skin (with dilatation of peripheral vessels);
- rapid breathing and heart rate;
- goosebumps and trembling;
- numbness and blueness of the limbs, ears, lips and nose;
- excessive tension in the neck muscles.
Signs of more severe hypothermia include:
- tissue pain;
- slow speech;
- convulsions;
- weakness, drowsiness;
- respiratory arrest;
- loss of consciousness;
- weak heartbeat and rare breathing;
- frostbite and rigor of the body, which is sometimes covered with frost or a crust of ice;
- frost and icicles on the eyelashes, in the mouth and nose.
Prognostic markers
The effect of hypothermia on a person is individual and unpredictable. Cases of successful resuscitation with good neurological outcome have been described when the core temperature was below 14°C. In most victims, this temperature caused generalized coagulopathy and rapid death.
Consequently, even extremely low values of core temperature are not a reason to refuse resuscitation measures. QT interval prolongation >500 ms and high-amplitude J-wave are predictors of fatal arrhythmias. Signs of cell lysis (hyperkalemia >7-10 mmol/L) and generalized coagulopathy (fibrinogen <0.5 g/L) suggest an unfavorable outcome.
Features of frostbite of specific parts of the body
Each part of the human body reacts in its own way to environmental influences. In some situations, hypothermia is local. In most cases, this problem affects the arms, legs and face.
Hypothermia most often affects the lower extremities. This kind of problem occurs when shoes get wet. It should be noted that the foot is an area of the body where there is practically no fat layer. This causes it to freeze faster. The consequences of hypothermia have a negative impact on the condition of the joints and the functioning of the genitourinary system. In addition, wet feet are the main cause of colds.
No less often, people get frostbite on their hands, in particular their fingers. If such a problem is detected, you should absolutely not rub the damaged area of the body. You should wrap your limbs in warm clothes and wait for help from a qualified specialist.
During strong winds or other unpleasant weather conditions, people often experience hypothermia on their faces. At the same time, they feel a slight tingling sensation in the nose and cheeks. To solve this problem, as in the previous case, it is not recommended to use the rubbing method.
Warming patients in cases of severe hypothermia
Place the patient in a horizontal position on the bed. Provide venous access with a thick venous cannula - 16-18 G. If necessary, consider central venous catheterization or insertion of an intraosseous needle. Assess the need for mechanical ventilation. Remember that the risk of cardiac fibrillation during intubation is very high.
Start monitoring standard vital parameters: blood pressure, pulse, ECG, temperature. The pulse oximeter will most likely not show a plethysmogram due to severe peripheral spasm; Oxygen therapy or increasing the oxygen concentration during mechanical ventilation should not be performed.
Attention. Severe hypothermia requires active warming of the patient. And if this is not done, or done incorrectly, the patient will die.
Start therapy with measures aimed at reducing heat loss - cover the patient’s limbs, neck and head with blankets, leaving the chest and face open. The extremities of victims, as a rule, have a lower temperature compared to the temperature of the “core”. An attempt to warm the entire patient can lead to a paradoxical result - a decrease in central temperature and blood pressure due to peripheral vasodilation and increased flow of cold blood from the extremities.
This situation is even more relevant if hypothermia is combined with frostbite of the extremities. In such cases, apply thermal insulating bandages to the limb and avoid heating them in warm water.
Choose a method of warming the victim that is available in your conditions. The point of application of heat is the patient’s chest (blankets with heat blowing, a bath with warm, 37°C, water) or the internal environment (lavage with warm, 37-40°C, solutions of the pleural or abdominal cavity, extracorporeal blood warming).
The use of radiation heaters, heating pads and electric heating pads, electric blankets, towels soaked in warm water, lavage with warm stomach solutions are ineffective methods of warming when it comes to adult patients. They are used if other methods of warming are not available. And also in cases where the central temperature is not much lower than 32°C.
Publications mention intravenous administration of warm solutions and warming of inhaled air as effective ways to warm patients with hypothermia. It is absolutely unclear on what the authors’ optimism is based and where the temperature rise figures they give – 2-3°C/hour – come from. I would not mention this if these statements and recommendations did not wander from one publication to another and did not confuse doctors. Simple thermodynamic calculations show that the contribution of these methods to warming patients is vanishingly small. At the same time, it is not worth administering cold intravenous solutions to eliminate hypovolemia, for obvious reasons.
Method of execution: patients are administered 1.5-2.5 liters of 0.9% sodium chloride solution intravenously (20 ml/kg body weight for children), heated to 43-45°C. The solution, if special heating systems are not available, must be administered as quickly as possible. Otherwise it will simply cool down. If a heating device is available, set the temperature to 42°C.
To heat the respiratory mixture, standard humidifiers from ventilators are used. It is necessary to use these methods, but you should not expect that they will be able to make a significant contribution to the elimination of hypothermia. The recommended rate of increase in body temperature is 1°C/hour. If such a speed cannot be achieved, they begin to warm the entire surface of the body, and not just the chest. Active warming measures are stopped when the central temperature reaches 33-34°C.
Historical reference
The first mention of the use of hypothermia as a therapeutic method is the recommendation of Hippocrates (460-377 BC) to cover wounded soldiers with ice and snow. Military surgeon Dominic Larrey (1766-1842) wrote that wounded officers who were kept close to the fire were less likely to survive severe wounds than infantrymen who were not kept warm. The effect of cold water on the human body was first studied by J. Curry in 1798. To find out the causes of death of sailors who were shipwrecked in winter, he immersed volunteers in water at a temperature of 9-10 ° C and studied the effects of artificial hypothermia. In the 1950s, deep hypothermia with a body temperature of 20-25°C was used to create a bloodless surgical field for heart surgery, but such cooling caused a lot of side effects. In 1968 at the Institute of Surgery named after. A.V. Vishnevsky, a group of scientists led by Academician A.A. Vishnevsky proved that with rapid cooling after the death of warm-blooded animals, the possibility of returning to life is measured in hours, while without cooling it is measured in minutes. During the same period, studies of milder forms of therapeutic hypothermia with a moderate decrease in body temperature to the range of 32–34 °C appeared, which demonstrated improved survival in patients with cerebral ischemia and traumatic brain injury. Additional animal studies in the 1980s demonstrated the ability of mild hypothermia to play a general neuroprotective role following blockade of blood flow to the brain.
Complications associated with rewarming
Warming causes vasodilation, which can lead to a sharp decrease in blood pressure or cardiac arrest. Hypovolemia and hypotension are eliminated by the administration of 0.9% sodium chloride solution. Catecholamines are used only for health reasons - the risk of heart fibrillation is very high. Disturbances of cardiac rhythm and conduction are very diverse, but most of them disappear after normalization of temperature. If possible, try not to prescribe antirhythmics, since their effect in conditions of hypothermia is unpredictable. When cardiac activity stops, the CPR algorithm is used.
And finally, just a little about frostbite.
Exposure to low ambient temperatures initially leads to a decrease in blood circulation in the skin. During the first stage of frostbite, the skin loses sensitivity, and blisters and swellings may form. After warming up, swelling and relatively tolerable pain occurs. During the second stage of frostbite, the blisters formed on the skin disappear within 12–24 hours. And at the third stage, deep frostbite occurs, reaching the deep layers of the skin, and irreversible tissue necrosis occurs.
We hope this brief excursion into the pathophysiology of freezing and hypothermia will warm you up while waiting for the chimes to strike.
Sources: 1. Silbernagl S., Lang F. Taschenatlas der Pathophysiologie. – Georg Thieme Verlag, 2013 2. Chereshnev V. A., Yushkov B. G. Pathophysiology. – 2001.
