TUAT

In order for the reactions in our body to be carried out in a healthy way, a certain temperature is needed. The temperature required for these reactions is called body temperature. Despite temperature changes of 40-50 degrees in the external environment, the body’s internal temperature remains constant. However, at different times of the day and during ovulation in women, body temperature rises by half a degree. When the body temperature rises above 40 degrees Celsius, changes in protein structure and disruptions in chemical reactions begin. When the temperature drops, chemical reactions slow down and the functioning of vital organs is disrupted. Hypothermia, which occurs in the winter months during prolonged exposure to cold weather, can lead to death if left untreated. When the body temperature rises above a certain value, it is called hyperthermia and when it falls, it is called hypothermia. Both conditions are life-threatening.

Body temperature is normally measured at 36.8ºC±0.4. However, fluctuations of 0.5-1ºC during the day are considered normal. Oral temperature is 0.5ºC higher than axillary temperature and rectal temperature is 1ºC higher. The central and peripheral vascular system are the organs that function together with the hypothalamus in regulating body temperature. Normal body temperature is governed by the thermoregulatory center in the anterior hypothalamus. The endocrine system, skin and muscles are other auxiliary organs involved in body temperature regulation. Body temperature is usually measured with underarm thermometers. However, since these instruments are highly affected by the external environment and most of them do not have a dial below 35ºC, they do not accurately reflect the body center temperature. The most accurate measurement for internal temperature (core temperature) can be made using intravesical, rectal or esophageal probe thermometers. Rectal and esophageal thermometers are frequently used in clinical practice.

Causes of Heat Loss in the Body

Heat loss of the body occurs in four different ways: radiation, convection, conduction, evaporation.

  1. a) Radiation (Heat emission): It is the way the body loses the most heat under normal conditions. It covers 55-65% of body heat loss. Energy loss increases 2-5 times more in motion. As the ambient temperature decreases, the heat lost through radiation increases.
    b) Convection (air movement on the body surface): This is the most common cause of hypothermia in nature as heat loss increases with the speed of air movement. There is a layer of air about 4-8 mm thick that is immobile on the skin and acts as insulation. Heat is continuously supplied from the body. The movement of this layer increases heat loss. As this layer moves with the wind, heat loss increases. Proper dressing greatly reduces this type of heat loss.
    c) Conduction (Heat conduction): Heat transfer occurs when the body comes into contact with a colder conductor. 3-4% of heat losses occur in this way. Conduction is the cause of hypothermia in falls into water. As a result of getting wet or staying in water, heat loss through conduction is 25-30 times more than air and heat loss through direct contact with concrete or stone is 100 times more than air.
  2. d) Evaporation (Evaporation): It generally occurs as a result of the body sweating through the skin. Especially in hot weather, heat loss can reach 25%. Heat is also lost for heating and humidifying the air taken in.

Etiological factors

Changes in environmental factors, malnutrition at an advanced age or at a very young age, physical fatigue, metabolic causes, including hypoglycemia, hypothyroidism, hypoadrenalism, hypopituitarism, diabetic ketoacidosis, lactic acidosis, as well as central nervous system disorders, Many factors such as head trauma, tumor, stroke, Wernicke’s encephalopathy, medulla spinalis injuries, drugs, especially ethanol sedative hypnotics, sepsis, burns, exfoliative dermatitis and massive fluid or blood transfusion may play a role. Cold, rainy and windy weather can cause hypothermia even in healthy individuals. It is important to remember that hypothermia can occur in all geographical conditions, not only in people living in cold regions.

The thermoregulatory center regulates body temperature according to signals from the external and internal parts of the body. When heat loss increases and the body starts to cool down, some mechanisms are activated to raise the temperature. One effective mechanism is the contraction of skin vessels. When the vessels on the outer surface constrict, warm blood is directed to the internal organs and the brain to maintain body temperature. Shivering and voluntary movement of our muscles are also mechanisms to prevent heat loss. Some chemical mechanisms are also activated to increase body temperature. For example, thyroid hormones are molecules that are effective in raising body temperature. These hormones trigger certain enzymes to break down ATP, the body’s energy source, to release energy.

When, despite all precautions, the thermoregulatory center is unable to maintain the body’s temperature against temperature loss, the body temperature begins to drop and hypothermia occurs. A person is considered to be hypothermic when their body temperature falls below 35°C. The failure of the thermoregulatory center to function is often due to the body losing more heat than it produces. There are many factors that can cause this, but the most obvious is exposure to cold. Although it usually occurs in winter, there is a risk of hypothermia even in summer. The first sign of hypothermia is feeling cold. If we feel cold even though we are moving, if we have difficulty doing fine work such as writing, and if we feel a slight slowdown in our movements, the risk of hypothermia has started. Staying behind the group during group mountain hikes can be considered an early warning for hypothermia. As hypothermia deepens, brain functions slow down. Behaviors such as not realizing that one is cold despite the cold weather, for example not covering the front of one’s coat, indicate that brain functions have already begun to be affected. Stopping shivering is the first sign of severe hypothermia. The muscles stiffen and the person can no longer walk. Breathing and pulse become so weak that it is difficult to tell whether a person in severe hypothermia is alive or dead.

Pathophysiology

Body temperature is maintained at a constant equilibrium temperature between heat gain and loss. The response of different organ systems to low temperatures differs between individuals. The elderly are prone to hypothermia due to loss of shivering and convection properties, while children are prone to hypothermia due to their large body surface area. When the body temperature drops below a certain value, some changes begin inexorably. These are compensatory mechanisms and are aimed at raising body temperature. Mechanisms such as shivering, heart rate and blood pressure increase. However, when the body temperature drops below 32 ºC, adynamic changes begin and metabolism slows down. This leads to a decrease in oxygen consumption, carbon dioxide in expiration decreases and accumulates in the body. Negative inotropic and chronotropic effects begin to be seen in the body. As hypothermia deepens, the effect on the heart becomes more pronounced and malignant arrhythmias are activated. In this situation, the brain tries to prevent deep neurological pictures by reducing oxygen consumption. Therefore, theropathic hypothermia occurs. The number and depth of respirations decrease in the patient due to lung involvement. The risk of aspiration pneumonia increases as a result of loss of cough and gag reflex. Partial oxygen pressure and carbox dioxide pressure in the blood may be falsely high and pH may be low. Therefore, arterial blood gas should not be taken until the body temperature is raised to a certain degree. As hypothermia deepens, the oxyhemeoglobin dissociation curve shifts to the left as hemoglobin release of oxygen to tissues decreases. Diuresis develops as renal functions deteriorate. They are at risk for rhabdomyolysis, myoglobunuria and acute kidney injury. In addition, depending on the depth of hypothermia, plasma transfer to extracellular space increases and hemoconcentration develops. This leads to thrombosis, embolism and impairment in coagulation enzymes. Cortisol and triod hormones are normal or slightly elevated in hypothermic patients. Although metabolism slows down in patients, hyperglycemia is common because insulin secretion decreases.

Clinic

Hypothermia affects all organs, especially the brain and heart. Hypothermia can be classified according to duration, temperature and etiologic factors (Table 1).

Table.1 General classification of hypothermia
By duration Acute hypothermiaChronic hypothermia Freezing time is less than 6 hoursFreezing time exceeds 6 hours
According to temperature Mild hypothermiaModerate hypothermia

Severe hypothermia

32°C to 35°C28°C to 32°C

Below 28°C

According to the etiological cause Primary Hypothermia
Secondary Hypothermia
Direct exposure of a healthy individual to the agent causing hypothermiaChronic diseases, poisonings, advanced age, more deadly

Hypothermia has three different forms depending on the temperature: mild, moderate and severe.

Mild Hypothermia: Body temperature is between 34-35ºC. The most practical way to recognize hypothermia is for people in a group to observe each other. Chills, especially in the hands and feet, mild incoordination and strong tremors occur. Muscle coordination decreases as body temperature drops. As hypothermia deepens, memory loss, slurred speech, difficulty walking and changes in consciousness occur. Failure to take corrective measures in this situation can lead to severe hypothermia.

Moderate Hypothermia: Body temperature is between 30-33ºC. There is a slowdown in whole body energy metabolism and functions. 02 consumption and CO2 production decreased in all tissues. The patient is in a stupor, tremors have disappeared. In hypothermia, with the cessation of shivering at 30-32°C, complete loss of coordination and muscle rigidity, inability to stand, confusion, and irrational behavior develop. At 28-30°C there is severe muscle rigidity, semi-consciousness, mydriasis, superficial respiration and filiform pulse.

Severe Hypothermia: Body temperature is below 28ºC. There is no shivering. Fainting and ventricular fibrillation develop below 28°C. Around 20°C, death occurs as a result of cardiac arrest. At 19-20°C, brain death is seen on electroencephalography. In conditions where body temperature cannot be measured objectively, it is difficult to recognize severe hypothermia. Since the jaws of people with severe hypothermia are tightly closed, rectal measurement should be preferred over oral temperature measurement.

Severe life-threatening dysrhythmias are observed in this period. Classical findings of hypothermia on electrocardiography (ECG) include Osborn (J) wave at the end of the QRS complex (Figure 1), PR, QRS, QT prolongations, atrial fibrillation or flutter, sinus bradycardia nodal rhythm, atrioventricular block, premature ventricular contraction, ventricular fibrillation and asystole. Sinus bradycardia occurs due to a decrease in depolarization of the pacemaker cells of the heart when the core temperature falls below 32ºC. Ventricular tachycardia and ventricular fibrillation are life-threatening dysrhythmias that occur in severe hypothermia. In hypothermic patients, the heart muscle is extremely sensitive to rhythm disturbances. Even rough examination of the patient can cause dysrhythmias.

Image 1. Osborn(J)dalgası

Effects of hypothermia on other systems; In the pulmonary system, tachypnea is observed first, followed by a decrease in respiratory rate and tidal volume. The risk of aspiration pneumonia increases with cold-induced bronchorrhea and suppression of cough and gag reflexes. Endocrine organ functions are well preserved in hypothermia. Since insulin secretion and glucose demand of tissues are reduced, blood glucose level is usually measured normal or high. Hypoglycemia may also be seen, especially when shivering is excessive. In addition, disturbance of consciousness ranging from confusion to coma, dilated and non-reactive pupils occur in the central nervous system. During this period, blood flow rate is slowed down. Despite the decrease in blood flow, ischemic complications are reduced because the brain tissue’s need for oxygen decreases even more. Hypothermia prevents the migration of pericytes during the ischemic period in the central nervous system and reduces the dysfunction of the blood brain barrier.

Laboratory Findings

Most of the devices used in laboratories are standardized to 37°C. Therefore, it should be kept in mind that abnormal laboratory results may be due to device evaluation error. Since the blood gas results of the patients are adjusted according to the pH value of the instruments in the laboratory according to 37ºC, correction of the blood pH is necessary. The actual pH of the patient = read pH + (0.015 x (37ºC – measured temperature).

a) Mild hypothermia: Respiratory alkalosis may be observed.
b) Moderate and severe hypothermia: Hypoxia, metabolic or respiratory acidosis, increased amylase levels, leukopenia, thrombocytopenia, coagulopathy and electrolyte abnormalities are observed. For every 1°C of cooling, there is a 2% increase in hematocrit. While hyperglycemia is observed in acute hypothermia, hypoglycemia is observed in chronic and secondary hypothermia.

Treatment

The hypothermic patient arriving at the emergency room should be taken to the resuscitation room rapidly, wet clothes should be completely removed, if any, and a windless warm environment should be provided. O2 should be given at high concentration (approximately 100%) and intravenous (IV) fluid support should be provided. In hypothermic patients, IV glucose therapy should be administered due to decreased glycogen stores and masking of hypoglycemia symptoms and signs. Monitoring that can show body core temperature should be provided. Treatment should be planned according to the severity of hypothermia. Keeping in mind the cardiovascular collapse and dysrhythmias that may occur, exercise should be avoided as a heating method. The main goal in the treatment of hypothermia is active heating. Heating methods are divided into two groups as external (passive and active) and internal (active) heating according to the place of use.

   

1- Passive external heating: By covering with a blanket in a warm environment, the body is allowed to raise its own temperature by shivering. It is used in mild and moderate hypothermia.

2- Active external heating: Heated blankets, heating blankets, hot water bottles, chemical heat packs are placed on the neck, chest and groin parts of the body. Increasing body temperature by creating arterivenous anastomoses is a new active external heating technique. There are several methods of heating in this way. First method: subcutaneous vessels and arteriovenous anastomosis areas are heated with a heater emitting infrared B rays. These areas are the forehead, nose, ears, hands and feet. This method can increase blood flow up to 40 times. In other methods, hands and feet are heated by placing them in 45ºC hot water or by placing the forearm in a special device containing heated air with a negative pressure of 40 mmHg. However, the clinical usefulness of this application has not been conclusively proven and research is ongoing. Active external heating is used in mild to moderate hypothermia.

3- Active internal heating methods: These methods include heated IV fluids, humidified and heated O2, peritoneal lavage with potassium-free fluids, warm gastric lavage, extracorporeal machine heating methods and are used in severe hypothermia. In active internal heating; humidified O2 heated to 43-46ºC, IV saline solution heated to 43ºC at a rate of 150-200 ml per hour and potassium-free dialysis solution heated to 43ºC can be given up to 2 liters IV. In raising the active core temperature by closed thoracic lavage, warmed normal saline solution is administered through a wide thoracostomy tube inserted through the midclavicular line and withdrawn through another wide thoracostomy tube inserted through the midaxillary line. Pleural lavage with warmed saline has been observed to increase body temperature by 2.5ºC per hour. In open thoracic lavage, direct irrigation of the mediastinum after thoracotomy can increase the body temperature by 8ºC per hour. When mediastinal irrigation is performed with open thoracotomy, if the patient has a heart rhythm without perfusion, the left side is used, while in patients with perfusion, this application should not be used because it may trigger ventricular fibrillation. Possibilities of infection, bleeding and fluid overload must be taken into consideration in warming by these means. Gastric lavage with saline heated to 65ºC, which is among other ways of warming, raises the body temperature by 2.8ºC per hour. In patients who remain in cardiac arrest for a long period of time, extracorporeal warming of blood via cardiopulmonary bypass is beneficial. Especially in severe hypothermia, active external heating causes peripheral vasodilatation and diverts blood away from internal organs, while cold blood is directed towards internal organs. Thus, the core body temperature drops further and the incidence of dangerous dysrhythmias increases. This so-called “after drop” effect must be kept in mind during treatment. Pulse and respiration detection is difficult in hypothermic patients. Therefore, pulse and respiration control should be performed for 30-45 seconds. Since ventricular dysrhythmias due to hypocapnia may be observed in patients who need respiratory support, excessive ventilation should be avoided. If pulse and respiration cannot be obtained, cardiopulmonary resuscitation (CPR) should be started immediately. If the presence of a pulse is suspected, CPR should be applied again. In case of ventricular tachycardia or ventricular fibrillation requiring defibrillation, the patient is defibrillated once with 120-200 J with a biphasic defibrillator and once with 360 J with a monophasic defibrillator. For defibrillation, the patient can be connected to an automatic external defibrillation device. If the rhythm cannot be corrected, defibrillation is not performed again until the patient’s core temperature reaches 30ºC. In the meantime, cardiac compression and warming is continued. It may be difficult to achieve normal sinus rhythm in patients without adequate warming. The hypothermic heart may not respond to cardiac drugs, pacemaker stimulation and defibrillation. In addition, since drug metabolism is decreased, toxic findings may occur with repeated doses of drug administration. Therefore, drug administration should be avoided below 30ºC and dose intervals should be extended above 30ºC.

In physiologic sinus bradycardia due to cold, there is no need for medication and pacing and this condition improves spontaneously with warming. Since sinus bradycardia is due to decreased depolarization of pacemaker cells, anticholinergic agents have no place in treatment.

The success rate of CPR is low in patients with a history of fainting before hypothermia. In these cases, the physician has to deal with both hypothermia and other diseases that cause hypothermia (such as drug overdose, alcohol intoxication and trauma). Since vascular spaces will expand due to vasodilation during body heating, volume replacement should be performed in patients who remain hypothermic for more than 45-60 minutes, and ringer lactate should not be given because hypothermic liver cannot metabolize lactate. Routine administration of steroids, barbiturates and antibiotics has not been found to improve survival.

Prof. Dr. Şevki Hakan EREN

Gaziantep University Faculty of Medicine, Department of Emergency Medicine,

Doç. Dr. Abuzer COŞKUN

SBU Bağcılar Training and Research Hospital, Department of Emergency Medicine

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