The Vital Importance of Body Temperature: Dangers of Hypothermia and Hyperthermia

To ensure that our body’s reactions proceed healthily, a specific temperature is required. This required temperature for reactions is called body temperature. Despite external temperature fluctuations ranging from 40-50 degrees, the body’s internal temperature remains constant. However, there are half-degree increases in body temperature during different times of the day and during women’s ovulation periods. Once body temperature exceeds 40 degrees, changes in protein structure and disruptions in chemical reactions begin. Conversely, if temperature drops, chemical reactions slow down and vital organ function is impaired. Hypothermia, observed during prolonged exposure to cold weather in winter months, can lead to death if left untreated. Hyperthermia refers to when body temperature rises above a certain value, while hypothermia refers to when it falls below. Both conditions pose life-threatening risks.

Normally, body temperature is measured at 36.8ºC ± 0.4. However, fluctuations of 0.5-1ºC throughout the day are considered normal. Oral temperature is typically 0.5ºC lower than axillary temperature, and rectal temperature is 1ºC higher. The central and peripheral vascular systems, along with the hypothalamus, primarily regulate body temperature. The thermoregulatory center in the preoptic hypothalamus controls normal body temperature. The endocrine system, skin, and muscles also play auxiliary roles in regulating body temperature. Body temperature is usually measured using axillary thermometers, but these devices are significantly influenced by external conditions and do not accurately reflect core body temperature since many lack a dial below 35ºC. The most accurate measurement for core temperature (central temperature) is achieved using thermometers with intravesical, rectal, or esophageal probes. In clinical practice, rectal and esophageal thermometers are commonly used.

Reasons for Heat Loss in the Body

The body loses heat through four different pathways: radiation, convection, conduction, and evaporation.

1- Radiation (Heat emission): Under normal conditions, radiation is the primary way through which the body loses heat. It accounts for 55–65% of body heat loss. Physical activity increases energy loss by 2–5 times. As environmental temperature decreases, heat loss through radiation also increases.

2-  Convection (Movement of air over body surface): Heat loss through convection is a common cause of hypothermia cases in nature because heat loss increases with the speed of air movement. There is approximately a 4-8mm thick layer of still air on the skin surface that acts as insulation. Heat is continuously transferred from the body to this layer. Movement of this layer increases heat loss. Wind increases this movement, leading to increased heat loss. Proper dressing significantly reduces this type of heat loss.

3- Conduction (Heat transfer): When the body comes into contact with a colder conductor, heat transfer occurs. About 3–4% of heat loss happens through conduction. Hypothermia occurs when people fall into water due to conduction. Heat loss through conduction is 25–30 times greater in water or when submerged compared to the air, and 100 times greater when in direct contact with concrete or stone compared to the air.

4-  Evaporation (Vaporization): Typically occurs when the body sweats from the skin. Heat loss through evaporation can reach up to 25% in hot weather. Heat is lost when the air is heated and humidified.

Etiological Factors

Changes in environmental factors, inadequate nutrition at advanced or very young age, physical fatigue, and metabolic reasons such as hypoglycemia, hypothyroidism, hypoadrenalism, hypopituitarism, diabetic ketoacidosis, lactic acidosis, along with central nervous system disorders, head trauma, tumors, stroke, Wernicke’s encephalopathy, spinal cord injuries, medications especially sedative-hypnotics, sepsis, burns, exfoliative dermatitis, and massive fluid or blood transfusions can play a role in hypothermia. Cold, rainy, and windy weather can induce hypothermia even in healthy individuals, and it should be noted that hypothermia can occur in all geographical conditions.

The thermoregulatory center regulates body temperature based on signals from both external and internal regions of the body. When heat loss increases and the body begins to cool down, mechanisms to raise temperature come into play. One effective mechanism is vasoconstriction of skin blood vessels. When peripheral blood vessels constrict, warm blood is redirected to internal organs and the brain to maintain body temperature. Shivering and voluntary muscle movements also prevent heat loss. Chemical mechanisms also activate to raise body temperature; for instance, thyroid hormones are molecules that effectively increase body temperature. These hormones trigger certain enzymes to break down ATP, the body’s energy source, thereby releasing energy.

Despite all precautions, when the thermoregulatory center becomes insufficient in maintaining body temperature against heat loss, body temperature begins to drop, leading to hypothermia. When a person’s body temperature drops below 35°C, it is considered hypothermic. The main reason for the thermoregulatory center’s failure is usually that heat loss exceeds heat production in the body. Although there are many contributing factors, exposure to cold is the most apparent cause. While hypothermia is often associated with winter months, there is also a risk of hypothermia in summer. The initial sign of hypothermia is shivering. If shivering persists despite movement, experiencing difficulty in performing tasks requiring fine motor skills (e.g., writing), and noticing slight slowing in movements, the risk of hypothermia has begun. In group hiking, falling behind the group can be considered an early warning sign of hypothermia. As hypothermia deepens, cognitive functions slow down. Not realizing that one is cold despite cold weather, for example, not fastening the front of one’s coat, indicates that cognitive functions are beginning to be affected. Cessation of shivering is the first sign of severe hypothermia. Muscles stiffen, and the person becomes unable to walk. Respiratory and pulse rates weaken so severely that determining whether a severely hypothermic person is alive or not becomes extremely difficult.

Pathophysiology

Body temperature is maintained within a stable balance between heat gain and loss. Different organ systems respond differently to low temperatures among individuals. Elderly individuals are prone to hypothermia due to diminished shivering and convective heat loss capabilities, while children are susceptible due to their larger body surface area relative to mass. When body temperature drops below a certain threshold, inevitable changes begin. These are compensatory mechanisms aimed at raising body temperature. Shivering, increased heart rate, and mechanisms to raise blood pressure come into play. However, when body temperature drops below 32°C, more profound metabolic changes begin. This includes reduced oxygen consumption, decreased carbon dioxide production in expiration leading to its accumulation in the body. Negative inotropic and chronotropic effects are observed. As hypothermia deepens, cardiac effects become more pronounced, potentially leading to malignant arrhythmias. In response, the brain attempts to reduce oxygen consumption to mitigate severe neurological outcomes, leading to therapeutic hypothermia.

As hypothermia progresses, lung function is affected, reducing respiratory rate and depth. Reflexes like coughing and gagging diminish, increasing the risk of aspiration pneumonia. Blood gas analysis may show falsely elevated partial pressures of oxygen and decreased partial pressures of carbon dioxide due to the temperature effect, hence arterial blood gas should not be taken until the body temperature is raised to a certain degree. As hypothermia deepens, the oxygen dissociation curve shifts to the left due to decreased release of oxygen to tissues by hemoglobin. Renal function is impaired, leading to diuresis, and there is a risk of rhabdomyolysis, myoglobinuria, and acute kidney injury. Additionally, as hypothermia deepens, there is increased movement of fluid from plasma to the extravascular space, leading to hemoconcentration. This can predispose to thrombosis, emboli, and disturbances in coagulation enzymes. Cortisol and thyroid hormone levels in hypothermic patients remain normal or slightly elevated, despite overall slowing of metabolism and decreased insulin secretion contributing to hyperglycemia.

Clinical

Hypothermia affects all organs, primarily the brain and heart. It can be classified based on duration, degree of temperature, and etiological factors (Table 1).

 Mild Hypothermia:

Body temperature is between 32°C-35°C. The most practical way to recognize hypothermia is through observation among people in a group. Symptoms include initial cold sensation in the hands and feet, mild coordination problems, and strong shivering. As body temperature drops, coordination further diminishes, leading to memory loss, speech impairment, difficulty walking, and changes in consciousness. Failure to take corrective measures can progress to severe hypothermia.

Moderate Hypothermia:

Body temperature is between 30°C-33°C. There is a general slowdown in energy metabolism and functions across all body tissues. Oxygen consumption and CO2 production decrease. The patient is in a stupor state, with no more shivering. At temperatures of 30-32°C, complete loss of coordination, muscle stiffness, inability to stand, confusion, and irrational behavior occur. At 28-30°C, severe muscle stiffness, partial unconsciousness, dilated pupils, shallow breathing, and a weak pulse are present.

Severe Hypothermia:

Body temperature is below 28°C. There is no shivering. Below 28°C, unconsciousness and ventricular fibrillation occur. At around 20°C, cardiac arrest leads to death. Electroencephalography at 19-20°C shows brain death. Recognizing severe hypothermia can be difficult when body temperature cannot be measured objectively. In severe cases, rectal temperature measurement is preferred due to tight jaw closure. Severe hypothermia can lead to life-threatening arrhythmias.

a) Mild Hypothermia: Respiratory Alkalosis May Occur.

b) Moderate and Severe Hypothermia: Hypoxia, Metabolic or Respiratory Acidosis, Increased Amylase Levels, Leukopenia, Thrombocytopenia, Coagulopathy, and Electrolyte Abnormalities Are Observed. Hematocrit Increases by Approximately 2% for Every 1°C Decrease in Temperature. Acute Hypothermia Presents with Hyperglycemia, While Chronic and Secondary Hypothermias Exhibit Hypoglycemia.

TREATMENT

A hypothermic patient arriving at the emergency room should be promptly transferred to a resuscitation room. If wet clothing is present, it should be completely removed, and a warm, draft-free environment should be ensured. High-concentration (approximately 100%) oxygen should be administered, and intravenous (IV) fluid support initiated. Due to glycogen depletion and the masking of hypoglycemia symptoms, IV glucose therapy is recommended for hypothermic patients. Monitoring devices capable of displaying internal body temperature should be employed. Treatment should be tailored according to the severity of hypothermia. Exercise as a warming method should be avoided due to the potential for cardiovascular collapse and dysrhythmias. The primary goal of hypothermia treatment is active rewarming. Warming methods are categorized into external (passive and active) and internal (active) heating, depending on the use case.

Passive External Heating: Involves covering the body with blankets in a warm environment to facilitate self-generated heat production. Used in cases of mild and moderate hypothermia.

Active External Heating: Utilizes heated blankets, warming pads, hot water bottles, chemical heat packs placed on the neck, chest, and groin areas. Arteriovenous anastomoses are created to elevate body temperature. This method includes several approaches. The first method involves heating subcutaneous blood vessels and arteriovenous anastomosis areas with infrared B rays. These areas include the forehead, nose, ears, hands, and feet. This method can increase blood flow by up to 40 times. In other methods, hands and feet are heated by placing the forearm into a specially designed device containing 45°C hot water or by placing the forearm into a device with a negative pressure of 40 mmHg containing heated air. However, the clinical utility of this practice has not been definitively demonstrated, and research is ongoing. Active external heating is used in cases of mild and moderate hypothermia.

Active Internal Heating Methods: Includes warmed IV fluids, humidified and heated O2, peritoneal lavage with potassium-free fluids, warm gastric lavage, and extracorporeal heating methods, used in cases of severe hypothermia. In active internal heating, humidified O2 heated to 43-46°C, IV saline solution heated to 43°C, up to 2 liters, and potassium-free dialysis solution heated to 43°C can be administered IV. In closed thoracic lavage for raising active internal temperature, a wide thoracostomy tube placed at the middle clavicular line is filled with warmed normal saline solution and recovered from the second wide thoracostomy tube, placed at the midaxillary line. The pleural lavage with warm saline solution increases the body temperature up to 2.5°C per hour. With open thoracic lavage, the mediastinum can be directly irrigated after a thoracotomy to increase the body temperature up to 8°C per hour. If a patient is in cardiac arrest, and there is no blood flow, then the procedure is not necessary

Prof. Dr. Şevki Hakan EREN

Department of Emergency Medicine,
Gaziantep University Faculty of Medicine,

Assoc. Prof. Dr. Abuzer COŞKUN

Emergency Medicine Clinic,
Bağcılar Training and Research Hospital,
Istanbul Health Sciences University